'. A LABORATORY OUTLINE OF SMITH'S INTERMEDIATE CHEMISTRY SMITH'S INTERMEDIATE CHEMISTRY REVISED AND REWRITTEN BY JAMES KENDALL AND EDWIN E. SLOSSON 566 pp. With 15 illustrations and 125 cuts. NEW YORK, THE CENTURY CO. A LABORATORY OUTLINE OF SMITH'S INTERMEDIATE CHEMISTRY BY JAMES KENDALL PROFESSOR OF CHEMISTRY, COLUMBIA UNIVERSITY NEW YORK THE CENTURY CO. 1922 X COPYRIGHT, 1922, BY THE CENTURY C(X PRINTED IN U. S. A. **> PREFACE This laboratory outline is intended to accompany the revised edition of Alexander Smith's Intermediate Text Book of Chem- istry. It includes elementary experiments and some experi- ments from Alexander Smith's Laboratory Outline of College Chemistry. Many of the experiments are given in full detail, so that they can be used by students who are taking chemistry for the first time. JAMES KENDALL New York, May, 1922. CONTENTS 1. Substances and Properties 1 2. Capacities of Vessels 2 3. Weighing and Density 3 4. Changes in Metals Heated in Air 5 5. Mixtures and Compounds 6 6. Oxygen Preliminary 8 7. Glass-working 9 8. Oxygen Preparation and Properties 10 9. Hydrogen Preliminary 12 10. Hydrogen Preparation and Properties 14 11. Water Physical Properties 15 12. Hydrates 17 13. Quantitative Measurement of Water of Hydration . . 18 14. Weight of 22.4 Liters of Oxygen 19 15. Atomic and Molecular Weights 21 16. Composition and Formula of Nickel Sulphide .... 22 17. Composition and Formula of Oxide of Tin ..... 23 18. Solvents and Solubility 24 19. Solubility and Temperature. Saturation 26 20. Hydrogen Chloride Preparation and Properties ... 28 21. Chlorine Preparation and Properties 30 22. Sodium Hydroxide 31 23. Properties of Acids 32 24. lonization of Acids, Bases, and Salts 34 25. Ionic Materials 36 26. Equilibrium Between Undissociated Substance and its Ions 37 27. Double Decompositions Between Electrolytes in Solution 38 28. Bases and Acids 40 29. Neutralization 41 30. Solution of an Insoluble Base by a Strong Acid .... 42 31. Displacement 43 32. Non-Ionic Actions 44 viii CONTENTS EXERCISE PAGE 33. Titration of Bases and of Acids 45 34. Bromine . 47 35. Iodine 48 36. Comparison of the Halogen Compounds 50 37. Valence of a Metd by Displacement 51 38. Salts . . 56 39. Chemical Equilibrium in Double Decomposition ... 57 40. Hydrogen Peroxide 57 41. Hypochlorous Acid. Bleaching 59 42. Forms of Sulphur 59 43. Sulphides of Metals 61 44. Hydrogen Sulphide 61 45. Sulphur Dioxide 63 46. Sulphurous Acid 64 47. Sulphuric Acid 65 48. Percentage of Oxygen in Air 66 49. Carbon Dioxide in Air and in the Breath ...... 67 50. Ammonia 68 51. Hydroxide and Salts of Ammonium 70 52. Nitric Acid 71 53. Nitric Oxide 72 54. Nitrous Oxide 74 55. Phosphine and Phosphoric Acid 75 56. Arsenic Trioxide 76 57. Graphite . 77 58. Carbon Dioxide by Oxidation 77 59. Carbon Dioxide Preparation and Properties .... 78 60. Carbon Monoxide 79 61. Hydrocarbons . 80 62. Flame 82 63. Borax Bead Tests 83 64. Sodium Bicarbonate. Acid Salts 84 65. Hydrolysis 85 66. Potassium Nitrate Preparation 85 67. Recognition of Substances I 87 68. Recognition of Substances II (Negative Radicals) ... 88 69. Calcium Oxide and Hydroxide 90 70. Hard Water 91 71. Flame Tests (Positive Radicals) 92 72. Starch and Sugars . 93 73. Agriculture. Acid and Alkaline Soils 94 CONTENTS ix EXERCISE PAGE 74. Fertilizers 95 75. Fermentation 96 76. Acetic Acid 97 77. Destructive Distillation of Wood and Coal 98 78. Wood Charcoal and Bone Black 99 79. Tests for Food Components 100 80. Food Components of Milk 101 81. Food Components of Flour 102 82. Analysis of Baking Powder (Qualitative) 103 83. Esters. Soap 104 84. Colloidal Suspensions 105 85. How Soap Cleanses 107 86. Compounds of Magnesium 108 87. Aluminum Hydroxide. Alum 108 88. Dyeing 109 89. Reactions of Iron Compounds 110 90. Compounds of Lead. White Lead 112 91. Separation of Lead, Mercury and Silver (Metals of Group I) 112 92. Displacement of Metals. Couples 114 93. Manganese and Chromium . . . 115 94. Identification of Metals in Group II 116 95. Identification of Metals in Group III . . . . . . . 118 96. Identification of Metals in Groups IV and V .... 119 97. Recognition of Substances III (Metallic Elements) . . 120 APPENDIX I. Tension of Aqueous Vapor 122 II. Degrees of lonization in 0.1 N Solution 123 III. Apparatus Individual 123 IV. Apparatus General 124 V. Materials t . 125 GENERAL INSTRUCTIONS Read the "Regulations" posted in the laboratory. Read also, attentively, the following notes : Note 1 . Provide yourself with a note-book and make a careful permanent record immediately after each experiment. Enter the numbers and titles of the exercises of the outline systematically. State (1) what you did, if anything beyond the directions, but do not copy the printed directions them- selves, (2) what you observed, (3) what conclusions you drew. A sketch of the apparatus will enable you to recall the circum- stances of the experiment, if later reference to it is necessary. This note-book, when called for, is to be handed in for inspection. The blank pages in this Outline are not intended for the final notes. They may be used for individual suggestions given by the instructor, preliminary notes, record of weighings, etc. Note 2. Whenever an interrogation point or a direct ques- tion appears, a corresponding observation or answer should ap- pear in the note-book. The "(?)" indicates something to be observed and recorded. Note 3. The very numerous questions asked in the course of this outline are intended to be answered, not by speculation, but by careful observation and reasoning based on the results of this. Very often the student will find it necessary to devise and carry out further experiments of his own before a satis- factory answer is obtained. When a question occurs to you, endeavor by reflection and study to answer it yourself before consulting an instructor. Note 4. In many cases the work outlined could not in itself furnish the basis for an answer, and fuller investigation of the point would require work beyond the time or ability at the dis- posal of the beginner. Such questions are distinguished by references to Alexander Smith's Intermediate Text Book of Chemistry (revised edition), the page where the necessary in- formation may be obtained being indicated in bold type between square brackets. This text should be consulted, however, only i ii GENERAL INSTRUCTIONS after the experiments have been made and the notes written up as* far as possible. Cross-references to other experiments in this laboratory outline are given in ordinary type. Note 5. When a chemical change has been observed the equation should always be given in the notes, but an equation alone is never a sufficient record. Note 6. Where the word [Instructions] appears, consult the instructor before going further. Note 7. In quantitative experiments, marked [Quant.], use the finer balance; in all other cases the rough scales in the laboratory. Note 8. The expression [Storeroom] indicates that the necessary apparatus is not included in the individual outfits. Note 9. When the word [HOOD] appears, the operation is not to be conducted in the open laboratory. The apparatus is to be placed at once close to the desk-ventilator, or trans- ferred to the hood. Note 10. Where exact quantities are not indicated, very small amounts of solutions (1 c.c. or less) should be taken. This advice is given, partly to secure saving of material, but chiefly to avoid the waste of time which working with large quantities always entails. Note 11. To obtain the necessary chemical substances, if the chemicals are not furnished in "kits" to each student, do not carry the bottles from the side-shelf to the desk. Bring a clean test-tube for liquids and a watch-glass for solids. For the latter, a piece of paper, provided near the side-shelf, may also be used. When too much of any reagent has been taken, do not return it to the bottle. Note 12. The chemicals, if on a side-shelf, are divided into two sets, each arranged alphabetically according to the scientific names. The first set consists of solids in small bottles, the second of liquids. The bottles and their places are num- bered consecutively to facilitate accurate replacement, and scrupulous care must be taken not to disarrange them. Read the labels attentively, as there are frequently several kinds of the same substance (e.g., pure, commercial, dilute, concentrated, and normal). All materials are supplied through the storeroom service. Do not therefore take side-shelf bottles, when found empty, to the instructor, but to the storekeeper for refilling. GENERAL INSTRUCTIONS iii Note 13. The expression [From Instructor], however, in- dicates one of a few special substances for which the student must apply to an instructor. Note 14. The bottles on the desk, if there are any, con- tain certain substances which are frequently used. These substances will not be found on the side-shelf. Note 15. When any acid gets upon the clothing, apply ammonium hydroxide solution at once. Note 16. Burns, whether caused by contact with hot objects, by acids, or by corrosive liquids like bromine, are rubbed gently with a paste of sodium-hydrogen carbonate and water. All burns, save the slightest, must afterwards be dressed with an aqueous solution of boric acid (half -saturated) to prevent infection. Obtain the assistance of an instructor. Cuts must be washed in running water and dressed with boric acid as above, or with lanolin containing 2 per cent of boric acid. Note 17. All students work independently, except where cooperation of two students is expressly directed. LABORATORY OUTLINE OF INTERMEDIATE CHEMISTRY EXERCISE 1 SUBSTANCES AND PROPERTIES Object: To observe and record the properties of some substances. Apparatus: Graduated cylinder. Test-tubes. Rack. Evaporating dish. Wire gauze. Materials: 2 pieces each of white cotton cloth,* white mixed goods,* and woolen yarn. Sodium hydroxide (solution, 2%). Eosin or Acid Green (solution, 0.5%). Sulphuric acid (cone.). a. Place 60 c.c. of sodium hydroxide solution in the graduated cylinder. Divide the liquid equally between three test-tubes, immerse the pieces of cotton, wool, and mixed goods, one in each tube, and set the tubes in the rack. Attach the Bunsen burner by means of rubber tubing to a gas connection, close the air-holes at the base, and light. Now open the air-holes gradu- ally and note the effect upon the flame (?). Close the air-holes again, and hold a porcelain dish in the flame. What is deposited on the dish? What is the proximate cause of the dif- ference in the two flames? When using the burner for heating purposes, always regulate the air supply so as to get a noiseless, non- luminous flame. Heat the contents of the tubes one after another to the boiling point, FIG. 1 holding each by means of a piece of paper folded so as to give four thicknesses (Fig. 1). Then keep one above the flame, at the boiling point, but not bumping, for two * Before use, the cloth must be treated as in Ex. 88 o, to remove sizing. 1 2 CAPACITIES OF VESSELS minutes, then the second, then the third, then the first again and so forth. When the material in one of them has all dis- solved, examine all three. Record the results as follows: DISSOLVED IF CHANGED, APPEARANCE OF How LIQUID Cotton: Wool: Mixed goods: b. Place the wire gauze on a ring on the ring stand (Fig. 2). Fill the evaporating dish three-fourths full of water, add two drops of concentrated sulphuric acid, place it on the gauze and heat to boiling. Add 10 c.c. of the solution of the dye provided. Immerse one sample each of the cotton, wool, and mixed goods, so that they are com- pletely covered. Stir with the glass rod, and heat for 2 or 3 minutes. Pour the liquid into the sink and wash the materials thoroughly in clean water. Note the effect on each (?). FIG 2 c. If a microscope is available, place shreds of each sample, after drying, on a strip of glass and describe the appearance of the fibers as to structure (?) and color (?). d. Record the specific properties of wool and of cotton, both those observed in these experiments and those already known to you: natural color (?), natural structure (?), solubility in water (?), solubility in sodium hydroxide solution (?), effect of dyes (?). e. Smooth out the pieces of cloth and yarn on glass plates, or on bottles, to dry, and mount them in your notes. /. Wash out the test-tubes and dish thoroughly and put them away. Throw scraps of cloth into the jars, and not into the sink. Cleaning up in this way follows every experiment hereafter. EXERCISE 2 CAPACITIES OF VESSELS Object: To learn the capacities of several vessels by measuring the volumes of liquids they hold. WEIGHING AND DENSITY *6 Apparatus: Graduated cylinder. Test-tube. Evaporating dish. Flask. Materials: 2 small rubber bands. a. Place water in the graduated cylinder up to the 5 c.c. mark. The lowest point of the meniscus must be opposite the mark (Fig. 3). Pour this water into a test-tube and place a narrow rubber band round the test-tube at the level of the lowest point of the meniscus. Measure and place in the test-tube a second 5 c.c. of water. Mark with a second rubber band the new position of the meniscus. Make in your note-book a full-size drawing of the test-tube, and show the positions of the bands. Observe carefully the pro- FIG. 3 portions of the tube occupied by 5 c.c. and by 10 c.c. of water, so that when directed in future to use, say, "about 10 c.c." of a liquid or a solid you may be able to judge the amount by the eye. b. Fill the graduated cylinder with water to the highest mark. Fill the evaporating dish with water from the cylinder, note the volume of water remaining, and subtract to learn the capacity of the dish. Record all the figures in your notes. Repeat with the flask. c. What is the weight of 1 c.c. of water? What weights of water do the evaporating dish and the flask hold? EXERCISE 3 WEIGHING AND DENSITY Object: To learn to weigh and to learn how to measure densities. Apparatus: Balance (one for every 10 pupils). Evaporating dish. Graduated cylinder. 20 c.c. pipette. Materials: Roll sulphur. Sodium chloride (sat. sol.). a. Use of the Simple Balance [Instructions. Quant.]. By turning the screw attachment in front of balance case, release the beam and pans, allowing the beam to swing. Observe the excursions made by the pointer. Divide by two the total divisions covered by the pointer in one full swing, and count off from either end of the swing the divisions which this number designates, thus finding the position of the true zero point. The 4 WEIGHING AND DENSITY beam must swing freely during the observation: the zero is never to be read with the beam at rest. This observed zero point may lie a little to the right or to the left of the marked zero. Note down its distance, in scale divisions, from the marked zero. If it lies to the right prefix to the number of divisions the minus ( ) sign; if to the left the plus (+) sign. The zero of any one balance changes, and must be redetermined every time a weighing is made. Place a 10 g. weight in each pan [Note 1, below], and deter- mine the zero as before. Add the 0.01 g. weight to the right- hand pan, and find the reading about which the pointer now oscillates. The difference in reading between this point and the last determined zero point gives the deflection due to the 0.01 g. weight. It may be used for estimating weights less than 0.01 g. Thus, suppose the 0.01 g. weight causes a deflection of 5 divi- sions to the left (+5). When some body is being weighed, if the deflection is + 1, then 3- of the 0.01 g. or 0.002 g. must be subtracted from the sum of the weights. Note 1. Great care must be taken in the use of the balance and weights. The pans of the former must be let down upon their supports when not in use and every time weights or other objects are to be added or removed. All objects to be placed upon the pans must previously be carefully cleaned and dried. Solids are placed upon a watch-glass or upon a piece of glazed paper, and never directly upon the pans. The weights must be lifted from their case by means of forceps, never by the fingers. They are usually placed on the right-hand pan, the objects to be weighed on the left. Note 2. In reckoning results, count first by the places vacant in the box, and check by counting the weights themselves. This will enable you to avoid the commonest error in weighing, namely, miscounting the weights. Finally record the weights in the note- book, or laboratory outline, and never upon loose sheets of paper, as loss of the latter will necessitate a repetition of the entire experi- ment. b. Weigh an evaporating dish (dry) on the balance to the nearest decigram (0.1 g.) and record the weight. Place in the dish about 10 g. of pieces of roll sulphur (no particles or dust of sulphur), and weigh once more. Record the weight. The difference (?) is the exact weight of the sulphur actually taken. ~^ ^ , C CHANGES IN METALS HEATED IN AIR 5 Place in the graduated cylinder exactly 20 c.c. of water. Incline the cylinder and allow the sulphur gently to slide into the water in the cylinder. Read and record on the total volume. The increase (?) is the volume of the sulphur. Calculate from your data the weight of 1 c.c. of sulphur (?). This is the density of the sulphur. c. Record the specific physical properties of sulphur which you have observed, namely: color (?), crystalline or not (?), brittle or malleable (?), density (?), soluble in water or not (?). d. Wipe out the evaporating dish, and use the weight already recorded. Fill a 20 c.c. pipette to the mark with a saturated solution of common salt, allow this solution to run gently into the dish, and weigh again (record). The difference (?) is the weight of the brine. Calculate the density of the brine (?). EXERCISE 4 CHANGES IN METALS HEATED IN AIR Object: To observe changes in properties when a new substance is formed by the action of oxygen from the air. Apparatus: Balance. Porcelain crucible. Pipe-stem triangle. Meter stick (one for class). Piece of iron wire, No. 26. Materials: Copper wire (No. 30). Tin foil. a. Take about JTmeters of copper wire (No. 30), wind it round a pencil, and place the coil in the porcelain crucible. Weigh the whole on the balance, counting the weights as in 3 a (record) . Place the crucible (uncovered) in the pipe-stem triangle (Fig. 4) and heat, at first gently and then with the full Bunsen flame, for fifteen minutes. Now lower the flame to permit the crucible to cool gradually, and finally remove it. Weigh the crucible when cold (record). To what is the difference in weight due? Examine the coil (?), and bend the remains of the wire (?). Name the product, and make a condensed statement [9] of the change. Record the specific physical properties of the copper and of the product, namely: color (?), appearance (metallic or other- FIG. 4 wise ?), pliability or brittleness (?) of each. b. Fold up about 10 cm. square of tin foil and place it in the porcelain crucible. Weigh the whole on the balance (record) 6 MIXTURES AND COMPOUNDS and proceed as in a, par. 1. Stir the tin occasionally with a short piece of iron wire, but be careful to keep all the material in the crucible. Describe what you observe (?). Name the product (?) and make a condensed statement [9] of the change. Record the specific physical properties of the tin and of the product, namely, color (?), appearance (?), plia- bility (?) of each, and melting point of tin [507] (?) EXERCISE 5 MIXTURES AND COMPOUNDS Object: To learn how, by observing properties, to distinguish between mixtures and compounds. Apparatus: Magnet. Test-tubes. Funnel. Evaporating dish. Mortar. Trip scales. Bunsen. Materials: Iron powder. Carbon disulphide. [CAUTION: Ex- tinguish Bunsen flame while using this.] Filter-paper. Hydro- chloric acid (dil.). Sulphur. a. The Properties of Iron. Place about 0.5 c.c. of iron powder on a piece of paper. Examine it (?). Draw one pole of a magnet across the lower surface of the paper, noting the behavior of the iron (?). Transfer half the iron to a dry test-tube, add 2 c.c. of car- bon disulphide [CARE! Inflammable! Do not handle near a flame], and shake. Fold a filter-paper once, and then again at right angles to the straight edge. Open the paper as a cone, with a triple layer of OX^""X ^^^ \\ / paper on one side and a ' XA \/ single layer on the other, and place it in a glass y funnel (Fig. 5). Place jr IGf 5 the funnel in one ring of the iron stand, place the evaporating dish below the end of the stem, and pour the con- tents of the test-tube on to the paper. When the liquid has run through, open up the paper, so that the remaining liquid may evaporate. Place the dish in a draft, away from all flames, where its contents may evaporate also. While evaporation is going on, proceed with the operations described in the follow- ing paragraphs. When the paper and dish are dry, examine the MIXTURES AND COMPOUNDS 7 residue on the paper (?) and draw the pole of the magnet across the lower surface of the paper (?). Examine the dish (?). Is iron soluble in carbon disulphide (?). Place the other half of the iron in a test-tube, add a few drops of hydrochloric acid and note the odor [52] or absence of odor. Record the properties of iron, namely: color (?), effect of magnet (?), solubility in carbon disulphide (?), effect of hydro- chloric acid (?) and odor or not (?). b. The Properties of Sulphur. Pulverize some sulphur in the mortar, and repeat a using about 1 c.c. of sulphur instead of the iron. Record the properties of sulphur, not already studied in Exercise 3, namely: soluble in carbon disulphide or not (?), shape of crystals (sketch ?), effect of hydrochloric acid (?) and odor or not (?). c. A Mixture. On a piece of paper weigh out 3 g. of pul- verized sulphur and 5.5 g. of iron powder. Mix the powders as well as possible. Can the particles of the substance still be recognized or not? Pass the magnet underneath the paper (?). Place half the mixture in a test-tube, add 3-4 c.c. of car- bon disulphide, shake, and filter into the evaporating dish. When the liquid has evaporated, examine the residues on the paper and in the dish (?). Why does the result show that the material was a mixture, and not a chemical compound [13]? d. Place the remainder of the mixture from c in a dry test- tube, hold the test-tube by means of a piece of folded paper (Fig. 1, Ex. 1), and heat it gently in the Bunsen flame (?). When the test-tube is cold, place the lower end in the mortar, cover with a towel, and strike through the towel so as to break it. Use the pestle in this way until the material, and the fragments of glass to which the material is attached, can be placed in another test-tube. Add 2 c.c. of carbon disulphide, filter, and allow the filtrate to evaporate as before. Examine the material on the filter to ascertain whether it is iron (?). If it is in the least affected by the magnet, too little sulphur was used. Does the filtrate yield all the sulphur used (?), or any sulphur? Place the material on the filter in a test-tube, add a few drops of hydro- chloric acid (odor ?). Did either iron or sulphur give this odor? Record the properties of ferrous sulphide, namely: color (?), effect of hydrochloric acid (?) and odor or not (?). What was the effect of heating the mixture? Is the product an element, or a compound, or a mixture? 8 OXYGEN PRELIMINARY EXERCISE 6 OXYGEN PRELIMINARY Object: To learn which substances yield oxygen, and how to recognize . ^. Apparatus: Test-tube (hard glass). Clamp. Porcelain crucible. Dropper. Materials: Lead dioxide. Wooden splints. Sand. Potassium chlorate. Manganese dioxide (powdered). Sodium peroxide. Litmus papers. a. Place about 1 c.c. of lead dioxide (properties ?) in a dry hard glass test-tube, and fasten the tube in a vertical position in the clamp on the iron stand. Heat at first gently and then strongly with the Bunsen flame. Introduce a wooden splint, glowing at one end, into the tube until the spark almost reaches the oxide (?). What gas is liberated? What physical and chemical properties do you observe the gas to have? After removing from the flame, examine the residue in the tube (?). The new substance is litharge. Name the variety of chemical change illustrated [16]. b. Repeat a, using 1 c.c. of silicon dioxide (sand), and answer the same questions. c. Repeat a, using 1 c.c. of potassium chlorate (properties ?), and answer the same questions. d. Repeat a, using 1 c.c. of manganese dioxide (properties ?), having previously dried this by warming it in the porcelain crucible. Answer the same questions. e. Place in a dry test-tube about 0.5 c.c. of sodium peroxide. Using a dropper, add one or two drops of water to the peroxide (?). Test this gas with a glowing splinter of wood (?). After- wards, dip a piece of red litmus paper in the residual liquid (?). A blue color indicates the presence of an alkali [168] (sodium hydroxide). GLASS-WORKING 9 EXERCISE 7 GLASS-WORKING Object: To learn how to make simple apparatus. Apparatus : Triangular file. Rack. Wing-top. Test-tube (hard glass) and stopper (1-hole). Materials: Glass rod. Glass tubing. a. Glass Rod. Make a transverse notch about 15 cm. (6") from the end of a glass rod. To do this, hold the rod on the table and draw the edge of the triangle file once firmly and smoothly across it. Now, break the rod at this point by holding it so that the points of the thumbs are together on the side oppo- site to the notch, and pressing forward with the thumbs so as to bend the rod away from the- mark. Cut two other pieces of the same length. To remove the sharp, often jagged edges, hold the ends of the rods in the Bunsen flame, turning them slowly until the edges are rounded (fire-polished). Observe the color of the flame (?). To what is this color due [365]? Do not lay the hot rods on the table, but balance them across the test-tube rack or on an iron ring until cold. Why does heating the rods remove the sharp edges? 6. Glass Tubing, Drawing Out. Cut, exactly as in a, from a piece of glass tubing a portion m=s=a=!X!S=x ^^ 15 cm. long. Hold the center of ' this piece of tubing in the Bunsen r . ^ - " ^ flame, turning it slowly, until it becomes soft (Fig. 6). Hold and turn it, as a whole, carefully, so ^ F 6~"" as not to bend or twist it. When it is quite soft, remove it from the flame, and draw the two ends slowly apart. c. Glass Tubing, Bending. Fit a wing-top on the Bunsen burner, and use the luminous flame. Hold a piece of tubing 15 cm. long in the flame so that as long a portion is heated as possible, and rotate it steadily so as to heat all sides alike. Do not allow the tube to bend or twist. When the glass is quite soft, withdraw the tube and bend it to form a right angle, giving an L-tube (Fig. 7). The bend must be gradual and 10 OXYGEN PREPARATION AND PROPERTIES smooth, not sharp or crumpled. Bend another similar piece to form an obtuse angle. Fire-polish the edges (for this, use rcr Right FlG. 7 Wrong FIG. 8 the non-luminous flame), but do not heat too long, otherwise the bore will be diminished. d. Fit a stopper into the hard glass test-tube. Remove the stopper, and push the shorter end of the obtuse-angled tube through the hole (Fig. 8). Do not use force moisten the tube and the hole and rotate the tube while pushing it gently through (don't hurry). Allow the tube to project not over 1 mm. on the inside. Replace the stopper in the test-tube and test for air-tightness. To do this, place the end of the tube in the mouth, suck out some of the air, and note whether the tip of the tongue seems to adhere to the tube. Remove the tube and stopper, and repeat (?). What caused the tongue to adhere in the first instance? EXERCISE 8 OXYGEN PREPARATION AND PROPERTIES Object: To make a quantity of oxygen and to ascertain its physical and chemical properties. Apparatus: Mortar. Trip scales. Test-tube. Test-tube (hard glass) with stopper and bent tube (Ex. 7 d). Narrow rubber tube 12" long. Clamp. Pneumatic trough. 3 wide-mouth bottles. 3 glass plates. Deflagrating spoon. Iron wire. Materials: Potassium chlorate. Manganese dioxide (powdered). Splints. Asbestos paper. Sulphur. Red phosphorus. Char- coal (splinters). a. Pulverize 4 g. of potassium chlorate. Mix it on paper with 2 g. of manganese dioxide. Place about one-tenth of the V T" " OXYGEN PREPARATION AND PROPERTIES 1 1 mixture in a dry test-tube, heat it, and test the gas with a glowing splinter of wood (?). b. Place the remainder of the mixture in the hard glass test- tube provided with a stopper and glass tube (Ex. 7 d), and test for air-tightness. Moisten the end of a piece of narrow rubber tubing (12" long) and slip it over the end of the tube. Clamp the tube in a horizontal posi- tion (Fig. 9). Fill the pneumatic trough with water so as to cover the shelf or other support. Fill 3 wide-mouth bottles with water, cover them with glass plates, and invert them, one on the shelf, and the other two FIG. 9 in the trough. Use a small Bunsen flame to heat the tube and collect the first bubbles of gas in a test-tube filled with water and inverted over the exit of the rubber tube. Test this gas with a glowing splinter (?). What is this gas, and where did it come from? Now fill the bottles one by one, covering each when full with a glass plate, and setting it mouth upwards on the table. Dur- ing the operation, regulate the flame with great care so that the gas comes off in a steady, but not too rapid stream of bubbles. If the gas begins to come too fast, move the flame promptly to another part of the material and lower it slightly. The glass must not become hot enough to tinge the Bunsen flame yellow. Do not remove the flame, however, at any time, without first taking the rubber tube out of the water (Why?) After the third bottle is filled, remove the rubber tube from the water, let the test-tube cool and then fill it with water and set it aside. c. Line the deflagrating spoon with asbestos paper and place on the asbestos a little sulphur. Heat the sulphur until it catches fire. Observe the flame for a moment (?). Then lower the spoon into one bottle of oxygen (?), keeping the mouth as far as possible covered with the glass plate. How does the flame differ from that in air, and why? Is it finally extinguished? If 12 HYDROGEN PRELIMINARY so, why? Cautiously note the odor (?). Name the product (?) and state its physical properties (?). d. Reline the spoon with asbestos and place on it a little red phosphorus. Set fire to the latter, observe the flame (?) and lower the spoon into the second bottle as before (?). Name the product (?) and state its physical properties (?). Before putting the spoon away, heat both it and the asbestos strongly in the Bunsen flame to burn up all the phosphorus. e. Wrap the end of a piece of wire round a splinter of char- coal, set fire to the latter, and lower it into the third bottle as before (?). How does its combustion compare with that in air? Name the product (?) and state its physical properties (?). /. Record the physical properties of oxygen: color (?), odor (?), solubility in water (?). Record the chemical properties: glowing splint (?), sulphur (?), phosphorus (?), charcoal (?). What is the difference between a chemical and a physical property?* EXERCISE 9 HYDROGEN PRELIMINARY (Interaction of metals with acids and water) Object: To learn various ways of obtaining hydrogen and to compare them. Apparatus: 12 test-tubes. Graduated cylinder. Evaporating dish. Large beaker. Materials: Iron (nails). Zinc (gran.). Tin (gran.) Copper (shavings). Aluminium (wire). Magnesium (ribbon). Hydro- chloric acid (cone.). Zinc (dust). Sulphuric acid (dil.). Acetic acid. Calcium.** a. Place in separate test-tubes a few small pieces of each of the metals, iron (nails), zinc (granulated), tin (granulated), copper (shavings), aluminium (wire), magnesium (ribbon). Pour into the graduated cylinder 20 c.c. of pure concentrated * Exercise 14 (except /) may be introduced here, if desired. ** Calcium (metal) is most easily broken into small pieces by fixing it in a vise and using a chisel and hammer. ' t HYDROGEN PRELIMINARY 13 hydrochloric acid, add an equal volume of water, and mix. Add 5 c.c. of this diluted acid to the contents of each tube. Observe each case critically, and tabulate the results. Is there bubbling? If not, then warm gently (?). If the eye detects the formation of a gas or vapor, smell the contents of the tube (?). For comparison, take 5 c.c. of the acid by itself in a test-tube, smell it (?), warm and smell again (?). If heat- ing seems to produce a gas, remember that it may be the acid boiling, or steam and not hydrogen. The formation of hydrogen may be inferred from continued bubbling when heat is not being furnished, and may be proved by the slight explosion which follows when a light is brought to the mouth of the tube. If the gas is coming slowly, hinder its escape into the air by partially closing the mouth of the tube and let it accumulate before apply- ing the light. Number the metals in your notes in the order of their ap- parent activity (most active = No. 1). Do the bubbles appear on the side of the glass tube or on the metal? Why do they appear on one and not on the other? Record the properties of hydrogen you have observed: Gas, liquid or solid (?), soluble in water or not (?), colored (?), odor or not (?), unites with oxygen from the air or not (?) and if so when cold or hot (?). 6. After the action has ceased, filter any one of the solutions and evaporate (Ex. 10 /) 1 c.c. of it to dryness [HOOD] (?). What is the product? Record the action in each case in the form of a condensed statement [63]. c. Add some zinc dust to the remaining 5 c.c. of the acid (?). To what is the difference, if any, between the apparent activity of zinc dust and granulated zinc due? d. The same metals displace hydrogen from all acids. To illustrate, plA.ce a few pieces of zinc (gran.) in each of two test- tubes and add to one 5 c.c. of dilute sulphuric acid (?) and to the other 5 c.c. of acetic acid (?). e. Fill a test-tube with water, and invert it in the large beaker half filled with water. Place a small piece of calcium in the water and hold the test-tube over it (?). After the action has apply a light to the gas in the tube (?). Examine f water in the beaker (?) and test it with red litmus paper (?). 14 HYDROGEN PREPARATION AND PROPERTIES EXERCISE 10 HYDROGEN PREPARATION AND PROPERTIES Object: To prepare a quantity oj hydrogen and observe its physical and chemical properties. Apparatus: 90 c.c. gas-generating bottle with 2-hole stopper and thistle-tube. Glass tubing. 12" narrow rubber tube. Trough. Trip scales. Test-tubes. 2 wide-mouth bottles and 2 glass plates. Watch glass. Beaker. Wire gauze. Taper. Materials: Zinc (gran.). Sulphuric acid (cone.). Cupric oxide. a. Fit the 90 c.c. gas-generating bottle with a 2-hole stopper, a thistle-tube, and an L-tube (Fig. 10). Slip the narrow rubber tube over the end of the last. Place in the bottle about 20 g. of zinc (gran.). Test the apparatus to see whether it is air-tight. To do this, pour into the bottle through the thistle-tube enough water to cover the zinc. The lower end of the thistle-tube must also be under the water. Now blow through the rubber tube a little air, so as to force the water up the stem of the thistle-tube, and immediately com- press the rubber tube with the thumb and fore- FIG. 10 fi n g er - If "the water does not remain stationary, but gradually falls, there is a leak which must be remedied [Instructor]. Add concentrated sulphuric acid slowly through the thistle- tube until brisk bubbling sets in. Do not add more than one- fourth of the volume of the water already in the bottle. Place ijie end of the rubber tube in the trough. Collect a test-tube full of the gas. Close the tube with the thumb and carry it mouth downwards to a distant flame. Remove the thumb and, still holding the tube mouth downwards, set fire to the gas. Repeat this test until a sample is obtained which burns quietly. Why does it not do so at first? Do not at any tune attempt to light the gas at the exit tube. b. Collect over water two bottles of the gas. Cover the : with a glass plate and set it mouth downwards on the Light a taper, raise this bottle (still mouth downwards), ic the burning taper (?) almost to the bottom of the bottle and then withdraw it slowly (?). What happens to the Jas? WATER PHYSICAL PROPERTIES 15 What happens to the taper on insertion and on withdrawal? Explain. c. Set the other bottle mouth upwards on the table and leave it open for one minute. Then bring a lighted taper to the mouth (?). Explain. d. Fill a test-tube over water with the gas. Bring this tube, mouth downwards, mouth to mouth with a test-tube filled with air, and keep them in this position for 3 minutes. Then apply a light first to the lower (?) and then to the upper tube (?). What fact about the molecules of gases is shown by this experi- ment? e. Place 0.5 c.c. of cupric oxide in the bottom of a dry test- tube and fasten the latter in a horizontal position in the clamp on the iron stand. Insert a straight piece of glass tubing (ends fire-polished) into the rubber delivery tube and introduce this tube into the test-tube until the end touches the cupric oxide. Wait 3 minutes, to permit the air to be replaced by hydrogen. If the hydrogen is being given off too slowly, pour a little more sulphuric acid into the thistle-tube. Now heat the cupric oxide with a Bunsen flame. Note any change in the cupric oxide (?) and anything appearing in or on the cool part of the tube (?). Make a condensed statement of this action. What kind of chemical action is this [57]? /. Place 3 drops of the liquid from the gas-generating bottle on a watch glass. Place the watch glass on a beaker half filled with water, set the beaker on the wire gauze and boil the water. If the water in the beaker runs too low, because of evaporation, the vessel may crack. Add more hot water, if necessary. What is the solid left on the watch-glass by evaporation? g. Record the observed physical properties of hydrogen, namely: color (?), odor (?), density compared with air (?); also two chemical properties observed in b (?) and one in e (?) . EXERCISE 11 WATER PnrateAL PROPERTIES Object: To learn how to purify water, and how to find out whether it contains non-volatile impurities. Apparatus: Flask. Glass tubing. Test-tubes. Beakers. Clamp. Wire gauze. Watch-glass. 16 WATER PHYSICAL PROPERTIES Materials: Marble (chips). Potassium permanganate (sol.). Phenolphthalein (sol. in alcohol, 1:500). Ammonium hy- droxide (sol.). a. Put on a clean watch-glass 3-4 drops of distilled water, place the watch-glass on a 100 c.c. beaker half filled with water, and set the beaker on the wire gauze and boil (see directions in Ex. 10 /). Put on a second clean watch-glass 3-4 drops of tap- water and evaporate in the same way. Compare the two watch- glasses when dry (?). Do the specimens of water contain any non-volatile impurities? 6. Distillation. Bend a piece of glass tubing twice at right angles and fire-polish the ends. Connect with it, by means of a short piece of rubber tubing, a straight tube about 30 cm. long. Set up a flask and a test- tube immersed in cold water in the 300 c.c. beaker as in Fig. 11. Place in the flask about 100 c.c. of water, some marble chips (to prevent " bumping"), and a few drops of potassium permanganate solution. Boil the water and examine the distillate (in the test- FIG. 11 tube). . In what way has the water been purified by the distillation? Is potassium permanganate volatile under these conditions? If it had been, would distillation have puri- fied the water? c. Add one drop of phenolphthalein solution to some tap- water (?). Add one drop of ammonium hydroxide solution to some tap-water, and then add one drop of phenolphthalein (?) . d. Using a glass rod, add a single drop of ammonium hy- droxide solution to 100 c.c. of tap-water. Clean and use the same apparatus as in b, place this water in the flask, and distil as before. In each of six clean test-tubes place, from a glass rod, one drop of phenolphthalein solution, and use these test-tubes one after another to catch the distillate. Change the test-tube when 10 c.c. of liquid has come over until the six have been used. While changing, remove the flame and uncork the flask each time. If the water in the beaker becomes warm, change it for cold water. What evidence is there that ammonia passes over with the steam? Which portion of the distillate contained the most HYDRATES 17 ammonia and which the least? Cool the residue in the flask in running water, pour 10 c.c. of it into a clean test-tube and add one drop of phenolphthalein (?). Can water be purified from a volatile impurity? e. Name the common states in which water exists (?). How many states of water are known altogether [64]? EXERCISE 12 HYDRATES Object: To team how to find out whether a substance is a hydrate or not. Apparatus: Watch-glass. Test-tubes. Clamp. Mortar. Materials: Washing soda. Potassium chlorate. Aluminium sul- phate. Potassium sulphate. Barium chloride. Gypsum (frag- ments). Cupric sulphate. a. Place a clear crystal of washing soda (sodium carbonate) on a watch-glass and set it aside. At the end of the period, examine it and record any changes you observe (?). b. Place a clear crystal of washing soda in a test-tube and heat the crystal gently (?). What condenses on the walls of the tube? Explain the result of a [68]. c. Place in different test-tubes about 1 c.c. each of potas- sium chlorate, aluminium sulphate, potassium sulphate, barium chloride, and gypsum (calcium sulphate). Clamp one tube in a horizontal position, to prevent any condensed water from run- ning back and causing the tube to crack, and heat the substance with the tip of a small flame until no further change occurs (?) . Repeat with each tube. Record the results in tabular form as follows: SUBSTANCE WHAT AMOUNT OF APPEARANCE SUBSTANCE WAS HEATED CHANGE CONDENSED OF FINAL A HYDRATE WATER RESIDUE OR NOT The amount of the water condensed may be "great," "small," or "a trace." Remember that even an anhydrous substance may contain a little water, as an impurity. Hence, a substance is not to be classed as a hydrate (last column) unless the libera- tion of water is distinctly evident. 18 MEASUREMENT OF WATER OF HYDRATION Are all crystalline substances hydrates? Illustrate. Make a condensed statement of the change in each case in which water was given off. d. Take about 1 c.c. of copper sulphate crystals. Note their color (?). Pulverize them finely in the mortar and note the color again (?). Explain. Place the powder in a dry test-tube, clamp the latter in a horizontal position, heat the substance as in c and tabulate the results as before. Leave the tube in the clamp until it is cold, and then set it upright (?). If there is not enough water condensed to permit some to run down to the solid residue, add two drops (?). Note the color. What substance is formed? Make a condensed statement, showing the action to be re- versible [69]. Record its color under the name of each substance. EXERCISE 13 QUANTITATIVE MEASUREMENT OF WATER OF HYDRATION Object: To find the per cent of the elements of water in gypsum (hydrated calcium sulphate) or in barium chloride. Apparatus: Porcelain crucible. Balance. Pipe-stem triangle. Materials: Gypsum (powdered crystals). Barium chloride. a. Clean and dry the porcelain crucible and weight it to the nearest centigram (0.01 g.), counting the weights as in 3 a. Then place in it about 2 g. of pulverized gypsum (do not try to take this exact amount) and weigh again as before. Record the weights in tabular form as shown below. Support the crucible (open) on the pipe-stem triangle, placed on the ring of the iron stand, so that the bottom of the crucible is a short distance above the inner cone of the Bunsen flame. Lower the flame and heat at first very gently to avoid loss of any particles by sudden splitting of the crystals. Later use the full flame. After 15 minutes' heating, allow the crucible to cool and weigh to the nearest centigram. Replace the crucible on the triangle, heat again for 5 minutes, allow to cool and weigh again. If the weight is less than before, heat once more, and repeat until two successive weighings are identical, i.e., "heat to constant weight." WEIGHT OF 22.4 LITERS OF OXYGEN 19 What does this constant weight show about the water of hy- dration? Wt. of crucible + gypsum g. Wt. of crucible empty g. Wt. of gypsum taken g. Wt. after first heating g. Wt. of crucible + gypsum g. Wt. after last heating ^ g. Wt. of water of hydration g. wt. of water X 100 Per cent of water = ; = 7 wt. of gypsum When the percentages obtained by all who have done the experiment are compared, what law of chemistry is found to be illustrated? Record the average of the values found by all for the percentage. b. Some members of the class may be directed to use barium chloride, following otherwise all the directions given for gypsum. EXERCISE 14 WEIGHT OF 22.4 LITERS OF OXYGEN Object: To learn the weight of a measurable volume of oxygen. Also to make the necessary corrections and calculate the density and molecular weight of this, or of any other gas (quantitative). Apparatus: Trip scales. Porcelain crucible. Iron wire. Hard glass test-tube with 1-hole stopper, bent tube and narrow rubber tubing. 2-liter bottle. Trough. Thermometer (one for class). Barometer. Glass plate or cork. Balance. 500 c.c. graduated cylinder (1 for 10 pupils). Materials: Manganese dioxide (powdered, dried). Potassium chlorate (chemically pure, powdered, dry). a. Place 6 g. of pulverized manganese dioxide in the por- celain crucible (uncovered) and heat it with the full Bunsen flame for 5-6 minutes. During this time, stir it occasionally with an iron wire. While this is going on, insert an obtuse-angled tube in a one- hole rubber stopper which fits the hard glass test-tube (as in 20 WEIGHT OF 22.4 LITERS OF OXYGEN Fig. 8, Ex. 7 d). Fill a 2-liter bottle with water, invert it in the pneumatic trough, and arrange the apparatus as in Fig. 9, Ex. 8. Take 7 g. of dry, pulverized potassium chlorate and, when the manganese dioxide has cooled, mix the two substances thoroughly on a sheet of paper. Place the mixture in the hard glass test-tube. Weigh on the balance the test-tube and con- tents to the nearest centigram and record the result according to the table below (?). Replace the stopper in the test-tube, and test for airtightness (see Ex. 7 d). b. Heat the contents of the test-tube, beginning at the end next to the stopper, and collect all the gas in the bottle. Regu- late the heating so that you can at all times count the bubbles. Continue heating until gas ceases to come off, and then re- move the rubber tube from the water and allow the test-tube to cool. Lower the bottle of gas in the pan until, when the eye is on a level with the water, the latter is seen to be at the same height inside and outside. To accomplish this and the next operation, it may be necessary to incline the bottle. While the bottle is in this position, close it with a cork or glass plate and set it mouth upwards upon the table. Read and record the temperature of the water (?) and also the barometric pressure (?). If, at this point, there is not time to complete the experiment, the test-tube may be corked tightly and put away (upright) along with the 2-liter bottle and its contents. c. Weigh on the balance the test-tube and contents, and record the weight (?). To measure the volume of gas collected in the bottle, fill the 500 c.c. graduated cylinder to the top of the graduation, note down the volume of water, and pour the latter into the bottle. Repeat until the bottle is filled level with the mouth, and record in the table the total volume of water used. Wt. of test-tube and contents before heating g. Wt. of test-tube and contents after heating ^ Wt. of Oxygen g. Volume of Oxygen c.c. Temperature C. Barometric Pressure mm. Tension of aqueous vapor [658] mm Barometric pressure, corrected [471 mm. ATOMIC AND MOLECULAR WEIGHTS 21 d. Reduce the observed volume of oxygen from the observed temperature and pressure to and 760 mm. [45-7]. e. From this reduced volume, and the weight, calculate the weight of 1 c. c. (the density) of oxygen. Wt. of oxygen ] TT^ i ~ n ~ - = x = wt. of 1 c.c. = density. vol. at and 760 mm. /. Calculate also the weight of 22.4 liters (the molecular weight) of oxygen [75]: wt. of 1 c.c. X 22400 = x = wt. of 22.4 1. = mol. wt. Compare the molecular weight found with the atomic weight of oxygen (?). How many atoms of oxygen are there in one molecule of the element? EXERCISE 15 ATOMIC AND MOLECULAR WEIGHTS Object: To find atomic weights from data given. Also to become familiar with the relations between density and molecular weight a. The corrected weights of one G.M.V. (22.4 liters at and 760 mm.) of several compounds of carbon are as follows : Wt. 22.4 1. Wt. carb. Wt. hyd. Wt. ox. Formula Carbon monoxide 28.005. 12.005 16 Carbon dioxide . . 44 005 12.005 32 Methane 16.037 12.005 4.032 Ethylene 28.042 24.010 4.032 Glycerine (vapor) .... 92.079 36.015 8.064 48 What value should you select for the atomic weight of carbon [79]? Assuming the formulae and atomic weights to be, for hydrogen H = 1.008, for oxygen = 16, and for carbon C = ?, write the formulae for each of the five compounds. b. The density (wt. of 1 c.c. at and 760 mm.) of ethylene chloride is 0.00433 g., what is the molecular weight [75]? c. Using the weights in 22.4 1. given above, find the weight of 1 c.c. (the densities) of methane and carbon dioxide. COMPOSITION OF NICKEL SULPHIDE d. How do the densities of the five substances mentioned in a compare with that of air [86] ? e. The weight of zinc combining with 35.46 g. (one atomic weight) of chlorine is 32.68 g. The specific heat of zinc (metal) is 0.0936. What is the atomic weight of zinc [87] ? EXERCISE 16 COMPOSITION AND FORMULA OF NICKEL SULPHIDE Object: To find the composition and formula of nickel sulphide (quantitative) . Apparatus: Porcelain crucible and cover. Balance. Pipe-stem triangle. Materials: Nickel powder (reduced). Flowers of sulphur. a. Weigh the crucible (without cover) to the nearest centi- gram, counting the weights as in 3 a. Place about 2 g. of re- duced nickel (do not attempt to take this amount, exactly) in the crucible and weigh again. Put about 2 g. of sulphur in the crucible and place the latter on the pipe-stem triangle. Set the cover on the crucible, and heat gently so long as sulphur vapor burns [HOOD] at the chink between the crucible and cover. Heat strongly for 1-2 minutes. Then hold the flame against the upper portion of the crucible, so that every part receives a thorough heating. Allow the crucible to cool. When it is cold (not before) remove the cover and weigh. Tabulate the results as follows: Wt. of crucible + nickel g. Wt. of crucible empty t *| : Wt. of nickel taken g. Wt. of crucible + nickel sulphide g. Wt. of crucible + nickel g. Wt. of sulphur combined g. Wt. of crucible + nickel sulphide g. Wt. of crucible empty g. Wt. of nickel sulphide g. COMPOSITION OF OXIDE OF TIN 23 b. Calculate the percentage composition: wt. of sulphur X 100 9 Per cent sulphur = wt. of nickel sulphide wt. of nickel X 100 Per cent nickel = . , = r wt. of nickel sulphide c. Find the formula of nickel sulphide [99]. To do this, first obtain the atomic weights of nickel and sulphur from the table. Wt. of sulphur -T- at. wt. of sulphur = ? (factor 1). Wt. of nickel -r- at. wt. of nickel = ? (factor 2). The combining proportion of sulphur to nickel found in the experiment is therefore: At. wt. sulphur X factor 1 _ S X factor 1 At. wt. nickel X factor 2 Ni X factor 2 Divide above and below by factor 1. What is the formula? d. Make the equation for the union of sulphur and nickel to form nickel sulphide. EXERCISE 17 COMPOSITION AND FORMULA OF OXIDE OP TIN Object: To find the proportions of tin and oxygen in oxide of tin (stannic oxide) and the formula of the latter (quantitative) . Apparatus: Porcelain crucible. Balance. Pipe-stem triangle. Materials: Tin foil (free from lead). Nitric acid (cone.). a. Weigh the crucible (without cover) (?). Place in it about 1 g. of tin foil (do not try to take exactly 1 g.) and weigh again (?). Record the weights in tabular form (see below). Place the crucible on the pipe-stem triangle and add 5 c.c. of concen- trated nitric acid. In doing this, pour the acid over every part of the metal. Hold the burner in the hand and warm the cru- cible with a very small flame, stopping for a moment if there is a tendency for any particles to be spattered out of the vessel. When the contents are dry, use a larger flame and heat for ten minutes. Weigh when cold (?). 24 SOLVENTS AND SOLUBILITY The nitric acid oxidizes the tin. A brown gas, nitrogen tetroxide, and water are given off during the process. Wt. of crucible + tin g. Weight of crucible, empty _ ^ Wt. of tin taken g. Wt. of crucible + oxide of tin g. Wt. of crucible + tin Wt. of oxygen g. Wt. of crucible + oxide of tin g. Wt. of crucible, empty _ g. Wt. of oxide of tin g. 6. Calculate the percentage composition of the oxide of tin. c. Find the atomic weight of tin in the table and calculate the formula of the oxide. d. From the data obtained in Ex. 13, calculate the formula of the hydrate. Proceed as follows: Wt. of water -f- Formula wt. of water (H 2 = 2 X 1.008 + 16 = 18.016) = x. Wt. of residue *- Formula wt. of residue (CaS0 4 = 40.07 + 32.06 + 4 X 16 = 136.13) = y. wt. of water 18.016 X x = s(H 2 0) wt. of calcium sulphate" 136.13 X y ~2/(CaS0 4 )' Divide both x and y by y. This will give the smallest whole numbers which are in the same ratio. Then substitute these whole numbers for x and y in 2/CaS04,zH 2 O. In 13 6, the formula is 2/BaCl 2 ,zH 2 0, and the values of x and y are found in the same way. EXERCISE 18 SOLVENTS AND SOLUBILITY (With practical applications) Object: To find out how to hasten the process of solution, and the difference between solution and suspension. To learn what solvents dissolve certain common materials. SOLVENTS AND SOLUBILITY 25 Apparatus: Test-tubes and rack. Corks to fit. Mortar. Gradu- ated cylinder. Glass rod. Materials: Cupric sulphate (hydrate). Filter paper. Potassium permanganate. Powered rosin. Alcohol (95% denatured). Fat (or lard). Carbon tetrachloride. Paraffin. Gasoline (or benzene) . a. A mass dissolves at its surface only. The larger the total surface, the faster it dissolves. Take two large crystals of cupric sulphate of equal size and yjt of such size that each can be slipped into a test-tube. Pro- vide two dry test-tubes with corks to fit. Pulverize one of the crystals very finely in the mortar, so that no large particles are visible. Place the powder in one test-tube and the crystal in the other. Add from the graduated cylinder 20 c.c. of water to each. Cork the tubes quickly, note the time on a watch (?), and shake the tubes gently. When the powder has all dissolved, note the time again (?). Estimate the fraction of the original crystal which remains in the other tube, then continue shaking it until it also has dissolved, and note the time again (?). Compare the total times required to dissolve each (?). Why does pulveriza- tion make this difference in the rate of solution? To save time, in what form should you use a substance to be dissolved? b. Take again two nearly equal-sized, but smaller crystals of cupric sulphate. Fill two test-tubes with water. Put one of the crystals into one of the tubes. Drop the other crystal into the second tube (Fig. 12), so that it is covered by the water, but rests on a narrow strip of ordinary paper. Set both tubes upright in the rack. How long does each crystal take to dissolve? If you had to dissolve a large amount of ma- terial quickly, with the least expenditure of effort, how should you proceed (in answering, take the results of both a and b into account)? While the tubes are standing, go on with c, d and e. -p c. On to a strip of paper dipping under water (Fig. 12), drop a crystal of potassium permanganate (?). Ex- plain (?). d. Place 1 c.c. of powdered rosin in each of two dry test-tubes. Add to one 5 c.c. of alcohol and to the other 5 c.c. of water and shake both (?). 26 SOLUBILITY AND TEMPERATURE Pour the alcoholic liquid into a large beaker full of water. In what ways is a suspension like a solution (?) and how does it differ? Should you remove rosin (or varnish or a similar gum) from clothing with water? With alcohol? e. Place a small piece of lard, half the size of a pea, in each of two test-tubes. Add 2 c.c. of water to one and 2 c.c. of car- bon tetrachloride to the other and shake (?). How should you remove grease from clothing? (In removing a grease-spot, place the part flat on a piece of blotting paper, to absorb the solution, and rub the spot with a rag dipped in the solvent.) /. Use small pieces of solid paraffin as in e, employing water and gasoline or benzene as solvents. g. Take 10 c.c. of water in each of three test-tubes. To one add a single drop of alcohol and shake. Does the alcohol dis- solve? Add more alcohol, a few drops at a time, until about 5 c.c. have been added. Has the amount added yet become greater than the water can dissolve? To the second tube add carbon tetrachloride (or carbon di- sulphide) in the same way, and answer the same questions (?) . To the third add gasoline (or benzene) in the same way, and answer the same questions. If you had a mixture of sugar (which is soluble in water) with fat on a piece of cloth, how could you remove first one and then the other component of the mixture? EXERCISE 19 SOLUBILITY AND TEMPERATURE. SATURATION Object: To learn how to make a saturated solution, and to know approximate amount dissolved (approx. solubility). Also to study the influence of temperature on solubility. Apparatus: Test-tubes. Funnel. Watch-glass. 100 c.c. beaker. Trip scales. Graduated cylinder. Thermometer. Materials: Calcium sulphate (powdered). Calcium carbonate. Filter-paper. Potassium dichromate (cryst.) Sodium sulphate (Glauber's salt Na 2 SO 4 ,10H 2 O and anhydrous Na^SCX). Potas- sium carbonate (cryst.). Ammonium chloride (cryst.). a. Test of Degree of Solubility. Place 1 c.c. of powdered cal- cium sulphate in a test-tube and shake with 10 c.c. of water for SOLUBILITY AND TEMPERATURE 27 two or three minutes. Filter the mixture, catching the clear filtrate in a clean test-tube. Treat as in Ex. 11, a, to see whether any dissolved (?). Examine 1 c.c. of powdered calcium carbon- ate (chalk) in the same way (?). Compare the deposits on the watch-glasses (?). Which substance is more soluble? What conclusion should you have drawn from mere shaking with water, without completing the test? Was the solution you evaporated saturated? Was it con- centrated? What is a saturated solution? b. Pulverize 6 g. of potassium dichromate. Describe the change in color and explain it (?). Shake the powder with 10 c.c. of water in a test-tube until the liquid is saturated. What evidence is there that a good deal dissolves? Now warm the contents of the test-tube gently, with occa- sional shaking (?). Is the substance more or less soluble as the temperature rises? When all has dissolved, set the tube in the rack and examine it when it has cooled (?). Describe the contents. Warm the contents of the tube carefully (to avoid cracking the tube) once more until all has dissolved. Then hold the tube in running water to cool it rapidly (?). Describe the contents (?). Note two differences (in size of particles and in color) between the results of slow and of rapid cooling and ex- plain each (?). c. Supersaturated Solution. Heat some anhydrous sodium sulphate strongly in a porcelain dish and allow it to cool. Take about 10 c.c. of water in each of two test-tubes. To one portion add Glauber's salt, previously pulverized in a mortar, until, after shaking, a considerable excess remains undissolved. Satu- rate the other portion with the cold anhydrous sodium sul- phate in the same manner. Perform the last operation rapidly, taking care not to introduce any particles of the hydrate, and do not let the solution stand before use. Now decant the two liquids into clean test-tubes, disregarding the cloudiness of one of them. Then add a little of the anhydrous substance to the solution first made and a small crystal of Glauber's salt to the contents of the second test-tube and shake both (?). After a short time, examine the contents of each again (?). Interpret the results [120]. d. Properties of Solutions: Volume Changes and Thermal - JL Effects. [Quant.] Take about 25 g. of potassium carbonate 28 HYDROGEN CHLORIDE and determine its weight to the nearest tenth of a gram. As- suming the specific gravity of this substance to be 2, calculate the volume of the amount you have taken (?). Place in the graduated cylinder exactly 85 c.c. of water and take its tem- perature. What is the sum of the volumes of the water and the carbonate, separately? Add the weighed specimen of potas- sium carbonate to the water, dissolve by repeated inversion of the cylinder, closing the mouth of the latter with the hand, and read the volume of the solution (?). Read also the temperature of the solution immediately (?). Is there a change in volume, or in temperature, on dissolving these twg substances in one another? What relation exists between the sign of the thermal effect when a substance is dissolved in a nearly saturated solution of the same substance, and the change of solubility with temper- ature [243-5] ? What do you infer in this case? e. Repeat d, using about 25 g. of ammonium chloride (sp. . 1.5). Make the same observations and answer the same questions. EXERCISE 20 HYDROGEN CHLORIDE PREPARATION AND PROPERTIES Object: To obtain hydrogen chloride and to learn some of its proper- ties. Apparatus: Test-tubes. Glass rod. Watch-glass. Lens (one for class). Materials: Ammonium chloride. Calcium chloride. Potassium chloride. Sulphuric acid (cone.). Litmus paper. Ammonium hydroxide (sol.). Sodium chloride. Silver nitrate (sol.). Zinc (dust). Sodium-hydrogen sulphate (sat. sol.). a. Place 1 c.c. of any chloride (for example ammonium chloride NH 4 C1, calciuin chloride CaCl 2 , or potassium chloride KC1) in a test-tube and add 1 c.c. of concentrated sulphuric acid (?). Is the material boiling (feel the bottom of the tube. Sulphuric acid boils above 300)? Waft a little of the gas towards the nose, but do not bring the latter too near to the tube (odor ?). To learn the behavior of the gas with water vapor, blow the breath across the mouth of the tube (?). HYDROGEN CHLORIDE 29 Moisten pieces of blue and of red litmus paper with water ' (to dissolve the gas) and place them in the mouth of the test- tube (?). What chemical property does the result show the aqueous solution of the gas to possess? Dip a glass rod in ammonium hydroxide solution. Smell the rod (?). The gas which is dissolved in, and given off by this solution is ammonia (NH 3 ). Now insert the glass rod into the mouth of the test-tube (?). The product is formed from the ammonia gas and the hydrogen chloride gas. Light a wooden splint and plunge the flame into the test- tube (?). Does the gas burn or support combustion? Four properties of hydrogen chloride (or its solution) have been observed. Make a list of these, and note opposite each whether it is a physical or a chemical property. b. Of what elements is hydrogen chloride composed? What is its formula? What proportions by weight of the constituents are indicated by this formula? Write the equation for the original action by which, in a, you obtained the gas. Note that the three chlorides suggested will give, respectively, (NH 4 )HS0 4 , CaS0 4 , and KHS0 4 , as one of the products. Where is this one of the products? To which of the varieties of chemical change does this action belong [126]? c. Write the equation for the interaction of ammonia and hydrogen chloride. To which of the four varieties of chemical change [132] does this action appear to belong? d. Take 1 c.c. of sodium chloride in a dry test-tube and add 1 c.c. of concentrated sulphuric acid [126]. Place in a second test-tube 0.5 c.c. of silver nitrate solution. Dip a clean glass rod in water and hold the rod, with the adhering water in the gas issuing from the first test-tube for one minute. Then transfer the rod, with the adhering solution, to the liquid in the second test-tube. To obtain a better idea of this action, add to the same silver nitrate solution one drop of concentrated hydrochloric acid (?). e. Place on the watch-glass a few particles of zinc dust. Dip a glass rod in water, hold it in the hydrogen chloride as in d, and then place the drop of the aqueous solution of the gas on the zinc dust (?). What is the gas liberated (see Ex. 9 c)? Make the equation for this action (?). Name three other metals which would react in a similar way 30 CHLORINE with hydrogen chloride solution (?). Write equations for these three actions (?). /. Make the equation for the action in par. 1 of d, and write the name of the substance under each formula (?). Take 5 c.c. of saturated sodium-hydrogen sulphate solution. Add to it concentrated hydrochloric acid, a very little at a time, shaking the mixture after each addition (?). Examine the precipitate with a lens and describe the form of the particles (?). Make the equation for this action (?). Compare the two equations last written [127]. What sub- stance, by its escape as a gas from the mixture, permitted the first action to go to completion? If this substance had remained dissolved, what difference would this have made in the result? What substance, by its separation as a precipitate, permitted the second action to go to completion? Explain why the separation of a product permits the completion of an action (?) EXERCISE 21 CHLORINE PREPARATION AND PROPERTIES Object: To prepare chlorine and to observe some of its properties. Apparatus : Trough. Test-tube and cork to fit. Kipp's hydrogen generator [253] (one for class). Taper. Materials: Potassium permanganate. Hydrochloric acid (cone.). Ammonium hydroxide (sol.). Caution: Chlorine gas, when breathed, has a very irritating action in the throat. Breathing the vapor of alcohol (sprinkled on a handkerchief) or ammonia gives relief. Perform the following experiments in a HOOD, or place where there is a good draft. a. Fill the trough with water. Place in the test-tube a very few crystals of potassium permanganate and add cautiously a drop or two of concentrated hydrochloric acid (make sure that you do NOT add some other acid by mistake). Leave the tube open (uncorked). What is the color of the gas? As soon as the tube appears to be filled with the gas, close the tube quickly with the cork, invert the tube instantly in the water contained in the pan and pull out the cork. Keeping the mouth under the water, shake the tube and note whether or not the gas dissolves (?). UL SODIUM HYDROXIDE 31 b. Place about 1 c.c. of potassium permanganate in the 300 c.c. beaker. Add 2-3 c.c. of concentrated hydrochloric acid and cover with a glass plate. When the beaker is filled with the gas, move the plate aside and insert for a few seconds a jet of hydrogen burning at a nozzle attached to a Kipp's apparatus* (?). Keep the beaker covered as far as possible. While the hydrogen burns in it, is there any change in the color of the gas? Dip a glass rod in ammonium hydroxide solution and insert it into the gas left in the beaker (?). What gas was formed? Cover the beaker again and use for c. c. When the beaker from b has again become filled with chlorine, light a taper and plunge the flame into the gas (?). The wax of the taper is composed chiefly of compounds of carbon and hydrogen. The black product is carbon (soot). What compound must have been formed? Verify your conclusion by testing the gas with ammonium hydroxide on a rod (?). As soon as the last experiment is finished, take the beaker (covered) to the sink, and pour some ammonium hydroxide solu- tion into it. Cover the beaker again with the plate and shake, holding the whole over the sink, and finally wash out. d. What did you observe that showed chlorine not to be lighter than air? What two other physical properties and two chemical properties were observed? EXERCISE 22 SODIUM HYDROXIDE Object: To learn some of the properties of bases. Apparatus: Test-tubes. Glass rod. Materials: Sodium hydroxide (sol.). Litmus papers. Cupric sul- phate (sol.). Aluminium sulphate (sol.). Phenolphthalein (sol.). Ammonium hydroxide (sol.). a. Recall the action of sodium on water [60], as seen in the class-room. Write the equation for this action, and place the * If no Kipp is available, a single generating bottle may be used for the whole class, or each pupil may take zinc and hydrochloric acid in a bottle provided with a stopper, L-tube, rubber connection, and nozzle (Fig. 10, p. 14). 32 PROPERTIES OF ACIDS name of the substance under each formula (?). To which of the four varieties of chemical change [132] does this action belong? 6. Take 1 c.c. of sodium hydroxide solution and dilute it with 10 c.c. of water. Dip a clean glass rod in the liquid and taste it. [Immediately rinse the mouth out with water. Taste substances only when told to do so] (?). Dip red and blue litmus paper in the solution (?). Rub the liquid between the fingers (?). Use the same solution in c. c. To 1 c.c. of cupric sulphate solution add one-third of the diluted sodium hydroxide solution (?). Make the equation and attach to each formula the name of the substance (?). To which variety of chemical change [132] does this reaction belong? Where is the other product of the reaction and how should you proceed so as to separate the precipitate, and finally obtain the other product in solid form? d. To 1 c.c. of aluminium sulphate solution add a few drops (shake between drops) of the sodium hydroxide solution (?). Make the equation and answer the same questions (?). e. To the rest of the sodium hydroxide solution add one drop of phenolphthalein solution (?). Litmus and phenolphthalein are called indicators. How does each behave with a base? /. What substance have we previously found to have the same effect on phenolphthalein as has sodium hydroxide (Ex. 11)? What is its formula? Dilute 1 c.c. of ammonium hydroxide solution with 10 c.c. of water and try with it the tests in b and d (?). g. Make a list of the chemical properties you have found a base to possess (?). What radical is common to all bases, and confers these properties? EXERCISE 23 PROPERTIES OF ACIDS Object: To learn about ionization and ike properties of adds. Apparatus: Test-tubes. Glass rod. Materials: Sodium hydroxide. Hydrochloric acid (dil.). Litmus papers. Sodium hydroxide (sol.). Hydrochloric acid (cone.). a. Place a small piece of sodium hydroxide in a test-tube, add 2 c.c. of water, and shake (?). What property does the solution possess which the solid body lacked [175]? Accord- I \ N > PROPERTIES OF ACIDS 33 ing to the theory of ionization, what chemical change took place when the solid dissolved? Make an ionic equation for this change [182]. What evidence, based on the freezing and boiling-points of such a solution, shows that this change has occurred? How many new substances are produced in this action? Name them (?). 6. You dissolved hydrogen chloride in a drop of water (Ex. 20 d). Answer the same five questions as in a, and make the ionic equation. In the case of every other simple acid, base, or salt, would the answers always be the same, or would they in some cases be different? c. Take 2 c.c. of dilute hydrochloric acid and dilute it with 10 c.c. of water. Repeat with this solution the three tests described in Ex. 22 b, and record the results. d. When zinc (or one of certain other metals, Ex. 9 d) is placed in dilute sulphuric acid, what gas is liberated? jiMake the ionic equation for this action [185]. All soluble acids show the properties found in c and d. Make a list of these properties (?). e. Place 3 c.c. of sodium hydroxide solution in a test-tube. Add about 1 c.c. of concentrated hydrochloric acid. Is there evidence of chemical action (touch the back of the hand with the bottom of the test-tube)? Keep the mixture for /. Make the ordinary [173] and ionic [193] equations for this action, which is a " neutralization." /. Since acids and bases act oppositely on indicators, like litmus and phenolphthalein, it is possible to find out when the proportions of the two materials required for complete inter- action have been taken, for the mixture will then be without action on an indicator. Dilute the mixture prepared in e. Moisten a glass rod in it, and touch the edge of a piece of blue and of a piece of red litmus paper with it (?). If the blue turns red, there is excess of acid. Add sodium hydroxide solution a drop at a time, shaking between drops, and moistening the rod and testing as before. Continue until no effect is produced on litmus of either color. If, by accident, too much alkali is added, or if the mixture was alkaline in the beginning, use drops of dilute hydrochloric acid in the same way. 34 IONIZATION When the liquid is neutral to indicators, taste it by touching the tongue with the glass rod (?). Set the solution aside to evaporate by itself. When it has dried up, examine the solid. What is the form of the crystals? What is the substance? EXERCISE 24 IONIZATION OF ACIDS, BASES, AND SALTS Object: To compare the extents of ionization of various acids, bases and salts. Apparatus: Electrolytic cell and electrodes. Storage batteries or lamp-board (Instructor). Materials: Sodium chloride (crystals and 0.1 N solution). Sodium hydroxide (0.1 N sol.). Hydrochloric acid (0.1 N sol.). Am- monium hydroxide (0.1 N sol.). Acetic acid (0.1 N sol.). Am- monium chloride (0.1 Nsol.). Ammonium acetate (0.1 N sol.). Sugar (0.1 N sol.). Toluene. Dry hydrogen chloride. a. Ionization. Name several distinct methods by which we may ascertain experimentally whether a substance is ionized in solution or not, and may learn the extent of the ionization [183-90] (?). Define the term ionization, first in theoretical terms (?), and second in terms of the experimental evidence (?). The degrees to which aqueous solutions of many substances are ionized are given in Ap- pendix II. Constant reference to this will be necessary in interpreting the observations in this and succeeding exercises. The experiments of this exercise may be postponed until after the work in 25 or 26 has been done. The apparatus should be set up by FIG 13 *ke instructor an d explained to the class before use. Obtain [Storeroom] an electrolytic cell* (Fig. 13). Half fill * The cell consists of a glass, flat-bottomed, specimen tube (about 75 X 22 mm.) fitted with a two-hole rubber stopper in which a vertical groove has been cut to permit the escape of gases. The electrodes are pieces of tin about 10 cm. long. IONIZATION 35 no v-b.c. the cell with the substances named below in turn. See very particularly that the electrodes in the cell are not touching one another. Connect with the terminals on the lamp board* (Fig. 15), and note whether the lamp glows or not (?). The cell is in series with the lamp and, if the lamp glows, the solution is a conductor. If it does not glow, the solution is a non- conductor. Wash the cell and electrodes and wipe the latter very carefully after each trial. The following substances, or solutions, show the behavior typical of various classes of materials. After giving the result in your notes, name the class which is illustrated in each case. If the substance is a conductor, what con- clusion is to be drawn in regard to the condi- tion of the dissolved body? In each such case, write an equation showing the materials present in the solution, and write the name under the formula of each substance (?). FIG. 14a * A storage battery of three lead cells or five Edison cells in series may be used, but is always in danger of being ruined by short-cir- cuiting through carelessness. Protection by means of a fuse leads to continual interruptions of the work. Where direct current is employed in the lighting system, the best plan is to use the circuit through two resistances of such ratio to each other as to give the desired potential by the drop over one of them. Thus, if we place a 20-ohm, and a 3.5-ohm resistance on a 110- volt circuit (Fig. 14, diagrammatic), the potential drop over the lower resistance will be about 16.5 volts. If these resistances be of sufficient carrying capacity (say, 5 amperes), then four different current outlets may be provided each one with plenty of current for one of the elec- trolytic cells previously described. Each of these outlets is in series with a small battery lamp, used as an indicator of the flow of current through the cell (Fig. 15). Where alternating current only is available, a small rotary trans- former, now commonly employed for charging automobile batteries, may be used. 36 IONIC MATERIALS 1. Dry, crystallized sodium chloride (?). 2. Distilled water (?). 3. 0.1 N aqueous solution of sodium chloride (?). 4. 0.1 N aqueous solution of sodium hydroxide (?). 5. 0.1 N aqueous solution of hydrogen chloride (?). 6. 0.1 N aqueous solution of ammonium hydroxide (?), 7. 0.1 N aqueous solution of acetic acid (?). 8. 0.1 N aqueous solution of ammonium chloride (?). 9. 0.1 N aqueous solution of ammonium acetate (?). 10. 0.1 N aqueous solution of sugar (?). Now, dry the cell by washing first with alcohol and then with ether. 11. Toluene in the dried cell (?). 12. Hydrogen chloride dissolved in dry toluene (?). What Ho 0A/T7.S Resistance 60 Watt. Ward- Leonard $ Ohms Resistance FIG. 15 difference between water and toluene do tests 5 and 12 bring to light? Keep this solution corked up in a dry test-tube for use in 28 d. EXERCISE 25 IONIC MATERIALS a. Ionic Materials. Give the names and symbols (not for- getting the charges) of the three distinct substances (in addition to water) present in the aqueous solution of sodium chloride b. Give a concise comparative statement of the specific physi- cal properties (such as color, molecular weight, solubility, be- havior towards electrically charged bodies, physical state, etc.), of the ionic and the free forms of sodium, hydrogen, and chlo- rine (?). . UNDISSOCIATED SUBSTANCE AND ITS IONS 37 EXERCISE 26 EQUILIBRIUM BETWEEN UNDISSOCIATED SUBSTANCE AND ITS IONS Object: To study the equilibrium between the ionized and non-ionized parts of an electrolyte in solution. Apparatus : Test tubes. Glass rod. Materials: Potassium bromide (crystals). Cupric bromide (crys- tals). Cupric chloride (crystals). Cobalt chloride (sol.). Potassium permanganate (sol.). Potassium dichromate (sol.). Chrome-alum (crystals). Relations of the Undissociated Substance to its Constituent Ionic Substances (in Equilibrium). The ions of an electro- lyte and the remaining molecules are in chemical equilibrium [182]. What changes take place, respectively, when the solution is concentrated by evaporation and when it is diluted, as in a, below [188]? Can the proportion of molecules be increased otherwise than by concentrating the solution (see 6, below) [455]? With substances like sodium chloride and hydrogen chloride these changes cannot be perceived by the eye (why?). In the following instances (a and b) the ionic and undissociated substances are both perceptible to the eye, and their relations as described above may, therefore, be studied very easily. a. Make a solution of potassium bromide in water. What is the color of bromide-ion? Take 0.5 g. of cupric bromide in a dry test-tube. Add two drops of water and agitate for some time (?). Then add more water, a drop or two at a time, agitating vigorously, and giving the substance time to dissolve, if it can, after each addition. Continue the addition of water cautiously until the substance has all dissolved, and afterward until the change in color is complete, and then stop. What is the color of the molecules of cupric bromide? What is the .color of cupric- ion? Compare the color with that of cupric sulphate solution (?) and explain. Formulate the change which has been wit- nessed (?). b. Now take a fresh portion of cupric bromide and repeat the experiment as in a, stopping the addition of water at the green stage. Divide the mixture into two parts. To one add 38 DECOMPOSITIONS BETWEEN ELECTROLYTES 2-3 g. of solid potassium bromide and shake vigorously (?). To the other portion add 4-5 g. of solid cupric chloride (?). Interpret the results. The converse case, in which one of the ions is removed, and the dissociation is promoted, is discussed in d. c. Many ionic substances are colored, although the color does not always differ markedly from that of the molecules. Examine the following solutions, make a list of the ionic substances con- tained in them, with their formulae and charges, and note the color of each kind of ions: cobalt chloride, potassium perman- ganate, potassium dichromate, chrome-alum (this last solution freshly made by dissolving the solid). d. Just as the union of ions to form molecules may be pro- moted by addition of a substance yielding a common ion (? Ex. 26 6), so the reverse of this, namely, the dissociation of mole- cules into ions, may be promoted by the removal of one of the ionic materials. The removal of ions may be accomplished in several ways. (1) By union of the ion with some other ion, when the mole- cules thus formed are insoluble. This case will be illustrated next (see Ex. 27). (2) By union of the ion with some other ion, when the mole- cules thus formed, although soluble, are very little dissociated by water (see Ex. 29). (3) By discharge of the ion and liberation of its material, through transfer of the charge to another substance (see Ex. 31). (4) By decomposition of the ion, as in Ex. 6 e. (5) By the mere change in the valence (amount of the charge) of an ion, for this converts it into another substance of the same material composition. (6) By discharge of the ion and liberation of its material through electrolysis. This was illustrated in Ex. 24. EXERCISE 27 DOUBLE DECOMPOSITIONS BETWEEN ELECTROLYTES IN SOLUTION Object: To study some typical double decompositions between electro- lytes in solution. Apparatus: Test-tubes. Funnel. Watch-glass. Bunsen. DECOMPOSITIONS BETWEEN ELECTROLYTES 39 Materials: Silver nitrate (sol.). Potassium chloride (sol.). Cal- cium chloride (sol.). Sodium hydroxide (sol.). Cupric sul- phate (sol.). Hydrochloric acid (dil.). a. Precipitation. Place 3-4 c.c. of silver nitrate solution in a test-tube and dilute with water. Add potassium chloride solution cautiously and agitate continuously, until no further precipitation occurs (?). Filter, concentrate the nitrate by evaporation, and pour it into a watch-glass to crystallize (?). Two salts are obtained, one by precipitation and one by evapo- rating. Formulate the action (as shown below). In doing this, show the KC1 + K+ + 01- AgN0 3 * N0 3 - + Ag+ I Ti KN0 3 AgCl (dissolved.) Ti AgCl (solid) three main physical components of each of the original solutions and the relations of these components (in equilibrium) to one another in each case. Show also the molecular products formed when the solutions are mixed. Assuming that the solutions are approximately decinormal [189], ascertain the proportions in which the original components of the solutions are present before mixing (Appendix II). Learn also to what extent the molecular products will be formed by union of the ions [189] (Appendix II) and, in the case of an insoluble substance, how complete will be the precipitation (Intermediate Chemistry, table on inside of front cover). On the basis of this complete information, com- plete the formulation, using heavy arrows to show the main ten- dency in each equilibrium. Explain in detail, and one by one, in what way, and to what extent, each of the six original components is affected by the results of mixing. Name the components of the filtrate and explain how each is affected by the evaporation and crystallization. How does the formation of the precipitate of silver chloride illustrate Ex. 26 d (1)? Upon what factor does the complete- ness of the change depend? Is, or is not, silver chloride a highly ionized substance [176]? Aside from double decompositions, what means have we for learning of what radicals a salt (like silver nitrate) is composed? 40 BASES AND ACIDS b. To a little calcium chloride solution in a test-tube add sodium hydroxide solution (?). Exactly as in Ex. 27 a (second par.), formulate, study and explain the whole action. How does this illustrate (1) of Ex. 26 dl To what classes of electrolytes do the four molecular substances respectively belong? c. To a little cupric sulphate solution add a little dilute hydro- chloric acid (?). In what respects does the result differ from those in a and 6, and why? Can any acids be prepared by precipitation, and if so, which [364]? In future, formulate all ionic actions in the way indicated in a. EXERCISE 28 BASES AND ACIDS Object: To learn the properties of bases and adds. Apparatus : Test-tubes. File. Porcelain dish. Bunsen. Materials: Litmus (sol.). Phenolphthalein (sol.). Sodium hy- droxide. Hydrochloric acid. Marble. Iron nail. Toluene. a. Bases and Acids: Hydroxide-ion and Hydrogen-ion: In- dicators. Examine distilled water in respect to (a) taste, (b) behavior with litmus, (c) conductivity (done already, Ex. 24). b. Dissolve a small piece of sodium hydroxide in water and examine the solution in respect to (a) taste, by diluting a little and tasting one drop, (b) behavior with litmus, (c) behavior with phenolphthalein, (d) conductivity (see Ex. 24). These properties belong to aqueous solutions of all bases. Aside from the water, what component alone is common to all solutions of bases, and has the above properties? Name this component and give its formula (?). c. Examine an aqueous solution of hydrochloric acid in respect to (a) taste, (b) behavior toward litmus, (c) behavior with phenolphthalein, (d) conductivity (see Ex. 24), (e) action on a piece of marble, (f) action on an iron nail (clean this with the file before use). These properties are shown by all aqueous solutions of acids. Aside from the water, what component alone is common to all solutions of acids, and has these properties? Name and give the formula of this component (?). d. Take the solution of hydrogen chloride in toluene (Ex. 24) NEUTRALIZATION 41 and examine it in respect to (a) conductivity (done already, Ex. 24), (b) action on a piece of marble, dried in advance by heating in a dry porcelain dish for a few moments, (c) action on an iron nail (clean as before). Be sure that perfectly dry vessels are used in these experiments. What substance identified in c is absent from this solution? What difference between water and toluene, as solvents, does this result indicate? In what three other respects would the two solutions of hydrogen chloride be found to differ? EXERCISE 29 NEUTRALIZATION Object : To investigate the action of a strong add on a strong base. Apparatus: Laboratory scales. Graduated cylinder. Burettes. Beakers. Glass rod. Sandbath. Bunsen. Materials: Potassium hydroxide. Hydrochloric acid (cone.). Phenolphthalein solution. a. Neutralization (Union of H + and OH~). A considerable chemical change may occur not only in precipitation (see Ex. 27), but also when ions unite to form a substance which, although soluble, is very little ionized by water. Weigh out 5 g. (laboratory scales) of potassium hydroxide, dissolve it in a little distilled water in the graduated cylinder, add water until the total volume is 50 c.c., and pour the clear solution into a burette. Measure 10 c.c. of concentrated hydro- chloric acid in the graduated cylinder, mix it in a small beaker with 50 c.c. of distilled water, and pour this into a second burette. Now, into a small beaker or flask run 15 c.c. of the acid solution from the second burette, and then add to it two drops of phe- nolphthalein solution. Place the vessel under the first burette, read the level of the liquid in the burette, and allow the alkali to run into the acid drop by drop, stirring constantly, until the last drop confers the faintest perceptible pink tinge on the whole solution. If you do not at first succeed in stopping at .the right point, repeat the experiment. Note the volume of alkali used. Concentrate the solution on the sand bath until a drop deposits crystals on cooling, and then remove the dish from the sand bath promptly and set it aside. 42 SOLUTION OF AN INSOLUBLE BASE When sufficient crystals have appeared, dry them with filter paper and examine with respect to (a) form, (b) taste, (c) ex- posure to moist air, (d) action of a solution on litmus, (e) con- ductivity of aqueous solution (done already, Ex. 24). Construct a table comparing the substance in these respects with the materials from which it was made. Compare the substance with potassium chloride. How should you determine whether a substance obtained in this way contained water of hydration or not? Make the necessary experiments (?). Wash out the burettes. Following the directions in Ex. 27 a (second par.), formulate, study, and explain the whole action. Note, however, that there are here no insoluble substances. Show how this experiment illustrates Ex. 26 d (2). Express the change involved in every neutralization of highly ionized substances by means of the simplest equation. How may neutralization be defined, in terms of the hypothesis of ions? How may it be defined, taking account of all the facts, but omitting all reference to ions? Calculate the approximate concentration, in terms of a normal solution as unity, of the potassium hydroxide solution used above (?). From the volumes of alkali and acid used in neutralizing, calculate the concentrations of the diluted hydrochloric acid (?), and of the concentrated acid employed to make it (?), expressing the concentrations in terms of a normal solution. Calculate the number of grams of hydrogen chloride per liter in the dilute and concentrated acids, respectively (?). 6. Neutralization of Slightly Ionized and of Insoluble Sub- stances. Consider the degree of ionization of acetic acid (Ap- pendix II). To neutralize 1 liter of normal acetic acid, would more or less alkali be required than to neutralize 1 liter of normal hydrochloric acid? In what way, precisely, would the details of the change be different in the case of acetic acid [Appen- dix II]? Name some of the consequences of this difference. EXERCISE 30 SOLUTION OF AN INSOLUBLE BASE BY A STRONG ACID Object: To investigate the action of a strong add on a weak, insoluble base. DISPLACEMENT 43 Apparatus: Beakers. Funnel. Test-tube/ ,; c Wash-bottle. Sand- bath. Materials: Cupric sulphate (sol.). S^uum hydroxide *(sol.). Hydrochloric acid (dil.). a. Dilute a few drops of cupric sulphate solution with much water and add excess of sodium hydroxide solution (?). Fit a filter paper properly into a funnel (Fig. 5, p. 6). Filter the mix- ture, and wash the precipitate (?) and filter paper repeatedly with distilled water to remove soluble substances. Now place a clean test-tube below the funnel, perforate the bottom of the filter paper, and wash the precipitate through into the test-tube by means of a stream of water from the wash-bottle. To the suspended cupric hydroxide, cautiously add dilute hydrochloric acid in amount just sufficient to give a clear liquid. Concen- trate the liquid on the sand bath until a drop, removed to a watch-glass, shows signs of crystallizing when cold. Then remove the dish promptly from the sand bath and allow it to cool. Examine the crystals (?). Formulate this action as in Ex. 27 a, taking account, however, of the fact that one of the interacting substances is an " insol- uble" solid. Describe in detail the stages through which the final production of solid cupric chloride is accomplished. To what class of ionic chemical changes does the foregoing action belong? Answer the same questions in regard to the pre- cipitations of salts in Ex. 27. EXERCISE 31 DISPLACEMENT Object: To establish the order of a<9^ty of zinc and Apparatus: Beaker. Test-tubes. Funnel. Materials: Zinc (granulated). Cupric sulphate (sol.). Zinc sul- phate (sol.). Ammonium sulphide (sol.). a. Displacement. Place several pieces of granulated zinc in a dilute solution of cupric sulphate and set aside until the change is complete (test ?). Occasional agitation will hasten the change (why ?). Filter. What is the precipitate [186]? Preserve the filtrate. Before examining the filtrate, take a few drops of cupric sul- 44 NON-IONIC ACTIONS phate solution and a like amount of zinc sulphate solution in two test-tubes. Dilute each solution with water, and add to each ammonium sulphide solution (?). What is the precipitate in each case, and what ions are required to form it? To the filtrate from the first part of this experiment add ammonium sulphide solution (?). What ions were present in the filtrate? What changes did the metallic zinc and the cupric ions, respectively, undergo in the first part of the experiment? Formulate this change in #n equation. In the course of this experiment, what becomes of the molecular cupric sulphate (Ex. 26 d)? What substances could have been substituted for the cupric sulphate without affecting the result so far as the consumption of zinc and the precipitation of copper were concerned? What substances, besides zinc, would have precipitated copper [54]? What other elements, besides copper, are displaced by zinc? Which one of the elements displaced by zinc did we prepare in quantity by an action like the present (Ex. 10)? Formulate this action in terms of ions. What were the products of the action of zinc upon concentrated sulphuric acid? b. Formulate the following actions in terms of the hypothesis of ions: Free chlorine and bromide-ion. Free chlorine and iodide-ion. Free bromine and iodide-ion. Free iodine and sulphide-ion. Arrange these four elements in a series similar to the electro- motive series of the metals [209]. Where should you place fluorine in this series? EXERCISE 32 NON-IONIC ACTIONS a. Non-Ionic Actions. In previous class-room and labora- tory experiments we have observed the formation of electrolytes in other ways than those illustrated in this chapter. These ways are non-ionic, or not distinctly ionic. Give illustrations of such of these ways as you recall: acids, two ways, bases, one way; salts, four ways, together with the reference numbers of the laboratory experiments in which they occur (?). TITRATION OF BASES AND OF ACIDS 45 EXERCISE 33 TITRATION OF BASES AND OF ACIDS Object: To learn how to measure the quantity of an add or of a base continued in a given specimen (quantitative). Apparatus : Burette. Beaker. Glass rod. Materials: Normal acid. Sodium hydroxide (sol.). Phenol- phthalein (sol.). Vinegar (white). Litmus (sol.). a. A normal solution of any acid is one containing 1.008 g. of the hydrogen radical (H) per liter, accompanied, of course, by an equivalent amount of the negative radical of that acid. Thus, one liter of normal hydrochloric acid (HC1) will contain 1.008 + 35.46 g. of the acid. Similarly, a normal solution of a base contains 17.008 g. of hydroxyl radical (OH) per liter. Thus one liter of normal sodium hydroxide (NaOH) will contain 23.00 + 17.008 g. of the base. What weight of acetic acid (H)(C0 2 CH 3 ) is contained in one liter of the normal acid? What weight of potassium hydroxide in one liter of the normal solution of this base? b. Titration of a Base with a Standard Acid. Fill a burette with the normal acid. Allow some of the acid to flow out, until all air has been expelled from the tip, and until the meniscus has reached the graduated portion of the burette. Hold the burette so that the surface of the acid is on the same level with the eye, and read the level of the bottom of the meniscus. Observe that the graduation is downwards, so that a reading two-tenths of a c.c. above the 2 c.c. mark is 1.8 c.c. (not 2.2. c.c.). Record the reading (?). Take exactly 10 c.c. of sodium hydroxide solution in the graduated cylinder (dry this first). Pour it into a beaker. Rinse out the cylinder three times with a little water (about 5 c.c. each time). Set the beaker on a sheet of white paper under the burette, and add a drop or two of phenolphthalein solution (?). Stir vigorously with a very thin glass rod. Now allow the acid to run in a rapid succession of drops into the beaker. Stir vigorously after each addition of a few drops. As soon as the acid begins to decolorize the indicator round the point where it enters, proceed more cautiously. Add only one drop at a time, and stir. The aim is to have the solution dis- 46 TITRATION OF BASES AND OF ACIDS tinctly pink before the final drop of acid is added, and perfectly colorless when that drop has been allowed to flow in. If, at the first attempt, you overshoot the mark, wash out the beaker, and take a fresh portion of sodium hydroxide solution, read the ' ' level of the acid in the burette, and try again. When the titration has been successfully performed, read the level of the acid in the burette (?). Subtract the reading from that at the beginning (?). The difference (?) is the volume of normal acid required for complete interaction with (neutraliza- tion of) 10 c.c. of the solution of the base. c. Since one liter of the normal acid contains 1.008 g. of avail- able hydrogen, 1 c.c. of the acid contains 0.001008 g. of hydrogen radical. Calculate the weight of hydrogen radical used in your experiment (?) . How many figures in your result are significant? Neglect all figures, in subsequent calculations, beyond your limit of experimental error. Now, 1.008 g. of hydrogen radical interacts with 17.008 g. of hydroxyl (OH). Using the weight of hydrogen just found, cal- culate the weight of hydroxyl contained in the portion of base you took (?). Finally, using the proportion indicated in the formula NaOH, calculate the total weight of sodium hydroxide which contains the weight of hydroxyl you found (?). d. Knowing from the result of c the weight of sodium hy- droxide in 10 c.c. of the solution, calculate the weight per liter (?). Calculate the concentration of the solution in terms of a nor- mal solution of sodium hydroxide as unity (?). e. Titration of an Acid. Wash out the burette, fill it with the sodium hydroxide solution as in 6, and read the level of the meniscus (?). In c, par. 2, we found the weight of hydroxyl in 10 c.c. of this solution. Calculate the weight in 1 c.c. (?). We may now use this solution containing a known concentration of a base for measuring quantities of acids. /. Take exactly 10 c.c. of white vinegar in the graduated cylinder (dry this first). Pour it into a beaker, rinse the cyl- inder three times with water, and set the beaker on a piece of white paper under the burette. Add 4 drops of litmus solution, or enough to give the liquid a distinct, but not strong pink color. Stir with a thin glass rod. Now titrate this solution with that in the burette, exactly BROMINE 47 as described in b (third par.). In this instance the color ap- pears locally with the blue. Aim to stop when the tint is pinkish-violet, halfway between pink and blue. Repeat, if necessary to secure a sharp result. Then read the level of the meniscus (?) and subtract from the former reading to learn the' volume of base used (?). g. Using the weight of hydroxyl per c.c. found in e (second par.), calculate the weight of hydroxyl used in/ (?). Calculate the weight of acid hydrogen in the 10 c.c. of vinegar (?). Finally, using the formula of acetic acid (H)(C02CH 3 ), calculate the total weight of acetic acid in the 10 c.c. of vinegar (?).. How much is this per liter? What per cent? These methods, and others like them, are known as volu- metric methods, and are largely used in analyses made for commercial (as well as scientific) purposes. EXERCISE 34 BROMINE Object: To liberate bromine, to note its properties, and to try a test for bromides. Apparatus: Test-tubes. Mortar. Materials: Potassium bromide. Sulphuric acid (cone.). Man- ganese dioxide (powdered). Bromine. Carbon disulphide. Bromine-water. Chlorine-water. a. Take 1 c.c. of water in a test-tube and add slowly 2 c.c. of concentrated sulphuric acid. Pulverize about 0.5 c.c. of potassium bromide, add 1 c.c. of manganese dioxide, mix, and ir add the mixture to the diluted acid. Warm very gently with Jr*'* a small flame (?). Note the color (?) and odor [CAUTION] (?) J of the vapor. What was the color of the potassium bromide? ^~ Does a compound show the colors of elements contained in it? Should you expect it to do so? If any of the bromine vapor is condensing on the sides of the tube, describe its properties (?). Fill the tube up with water. Write the equation [200] (?). b. To about 10 c.c. of water in a test-tube add two drops of bromine [CAUTION: Do not spill upon the hands (200)]. Is the 48 IODINE bromine heavier or lighter than water? Shake. Is it soluble in water? Use this bromine-water in c. c. To 10 c.c. of water add about 2 c.c. of carbon disulphide, close with the thumb, and shake (?). Are the liquids miscible (mutually soluble)? To this mixture add a few drops of bromine-water from 6 and shake. Is the bromine, judging by the color, equally soluble in both water and disulphide? If more so in one, how much more (?) and in which? d. Test for a Bromide. Take a crystal of potassium bromide (color?) and dissolve it in 5 c.c. of water (color of solution ?J. Add 2 c.c. of carbon disulphide and shake (?). Why is the car- bon disulphide not colored by the bromine? Holding the tube steady, add now a drop or two of chlorine- water, and observe carefully whether any color appears, and, if so, in which layer of liquid (water layer or carbon disulphide) it makes its appearance (?). Why? Shake vigorously and allow the mixture to settle (?). What substance has been liberated? Write the equation [202] (?). e. Summarize the properties of bromine: color (?), odor (?), density of vapor compared with air (?), density of liquid com- pared with water (?), relative solubility in water and carbon disulphide (?). Has bromine or chlorine the greater affinity for potassium? EXERCISE 35 IODINE Object: To prepare some iodine and use it to observe the properties of iodine. Also to try a test for iodides. Apparatus: Evaporating dish. Mortar. 400 c.c. beaker. Test- tubes. Materials: Sulphuric acid. Potassium iodide. Manganese di- oxide (powdered). Alcohol. Carbon disulphide. Potassium iodide (sol.). Splints. Chlorine-water. Bromine-water. a. Pour into the evaporating dish 1 c.c. of water and add 2 c.c. of concentrated sulphuric acid. Pulverize finely about 1 c.c. of potassium iodide, add 2 c.c. of manganese dioxide, mix, and add the mixture to the acid. Place the evaporating dish upon the ring on the stand and set the beaker with about IODINE 49 50 c.c. of water upon it so that the vapor of the iodine may condense on the bottom of the beaker. Heat the mixture gently with a very small flame, which does not touch the dish. Observe the color of the vapor (?), and the crystals (form ?) on the bottom of the beaker. What was the color of the potassium iodide (?), and the form of its crystals? Are its crystals like those of iodine either in form or color? While the crystals are accumulating, proceed with d. b. Place in as many test-tubes 1 c.c. each of water, alcohol, carbon disulphide, and potassium iodide solution. Scrape some of the crystals of iodine off the bottom of the beaker with a wooden splint, add one crystal to the contents of each of the four test-tubes and shake (?). Is the iodine heavier or lighter than water? Tabulate the results as follows, giving the solvent (?), degree of solubility (slight, considerable, very great ?), and the color of the solution (look through it at a piece of white paper ?) : SOLVENT SOLUBILITY COLOR OF SOLUTION Water: Etc.: * The solution in alcohol is the lotion called "tincture of iodine." That in potassium iodide solution is used in testing for starch (Ex. 72 b). c. To the test-tube containing water and iodine, add an equal volume of carbon disulphide and shake (?). d. Test for an Iodide. Take a crystal of potassium iodide m (color ?) and dissolve it in 5 c.c. of water (color of solution ?). Add 2 c.c. of carbon disulphide and shake (?). Why is not the color of iodine visible? Holding the tube steady, add now a drop or two of chlorine- water, and observe carefully whether the color appears in the ^ carbon disulphide or in the aqueous layer (?) and what color it is (?). Then shake vigorously and allow the mixture to settle. What substance has been liberated? Write the equation [205] (?). To what variety of chemical changes does this one belong? e. Repeat d, using bromine-water instead of chlorine-water (?). /. Summarize the properties of iodine: color of solid (?), of vapor (?), density of vapor compared with air and with bromine 50 COMPARISON OF THE HALOGEN COMPOUNDS vapor (?), density of solid compared with water (?), solubilities in four solvents (?). Compare the affinities of chlorine, bromine, and iodine for potassium (?). EXERCISE 36 COMPARISON OF THE HALOGEN COMPOUNDS Object: To learn how a chloride, a bromide, and an iodide react with sulphuric acid, and to observe the properties of the hydrogen com- pounds of the halogens. Apparatus: Mortar. Test-tubes. Glass rod. Materials: Potassium chloride. Sulphuric acid (cone.). Litmus paper (blue). Ammonium hydroxide (sol.). Potassium bro- mide. Potassium iodide. Note : Remember that the hydrogen compounds of the halo- gens are all colorless. a. Hydrogen Chloride. Pulverize about 1 g. of potassium chloride (color ?), place it in a test-tube, and add 0.5 c.c. (not more) of concentrated sulphuric acid (?). Blow the breath across the mouth of the tube (?). Test the gas with moistened blue litmus paper (?). )' Lower into it a glass rod dipped in ammonium hydroxide solution, which will give off ammonia gas (?). Write the equation (?). ^Vj&n a\\l?$ b. Is any colored gas visible in a? Why is the color of chlo- rine not observable? c. Hydrogen Bromide. Repeat a in every detail, using po- tassium bromide; make the same notes (?) and answer the same questions (?). d. Is there a colored gas or vapor visible in c? Name it (?). How could you distinguish a bromide from a chloride? e. Hydrogen Iodide. Repeat a in every detail, using po- tassium iodide, make the same notes (?) and answer the same questions (?). /. Warm the tube from e (?). What is the colored vapor? Does it form crystals on the tube? Stop heating, and let the vapor condense. What gas can you recognize by its odor [CAUTION]? VALENCE OF A METAL BY DISPLACEMENT 51 Was this odorous gas formed from the potassium iodide or the sulphuric acid (in answering, consider the formulae of these sub- stances and of the gas)? By what sort of chemical action must this gas have been formed? Could hydrogen iodide have pro- duced such an action? Write an equation to illustrate your answer (?). Why, then, was iodine liberated? g. Using the results of this exercise, how could you recognize a bromide and an iodide, and distinguish them from a chloride? What other method of recognizing bromides and iodides did we learn before? EXERCISE 37 VALENCE OF A METAL BY DISPLACEMENT Object: To determine (1) the weight of hydrogen which is displaced by one at. wt. (24.32) of magnesium,* and (2) the valence of magne- sium. If, e.g., 24.32 g. of magnesium is found to displace (and combine in place of) one at. wt. (1.008 g.) of hydrogen, the atomic weight of magnesium is univalent. If it displaces two at. wts. of hydrogen (2.016 g.), it is bivalent, and so forth (quantitative). FIRST METHOD Apparatus: Balance. 200 c.c. flask. Stopper (1-hole). L-tube and rubber delivery tube. 2-liter (or 1-liter) bottle and glass plate or cork. Trough. 50 c.c. graduated cylinder. Funnel. Thermometer. Barometer. 500 c.c. graduated cylinder (1 for 10 pupils). Materials: Magnesium wire (2 mm. diam.), or iron piano-wire, or aluminium wire. Hydrochloric acid (pure, cone.). a. Take a piece of magnesium f wire weighing about 1.7 g. and determine (balance) its exact weight to the nearest centi- gram (?) ; tabulate the data as shown under d. Fit the 200 c.c. flask with a one-hole stopper, L-tube, and *With another metal the same directions and questions apply ^ provided only the name of the metal be substituted for that of mag- nesium throughout, and the appropriate atomic weight (iron, 55.84; aluminium, 27.1) is employed in the statement of the object and in d and e. If one method only is used, try the third. t Other metals, such as aluminium (wire, about 1.4 g.), may be used. 52 VALENCE OF A METAL BY DISPLACEMENT rubber delivery tube, and test for air-tightness (Ex. 7 d). Fill the 2-liter bottle* with water and invert it on the support in the trough. Place in the 500 c.c. graduated cylinder 20 c.c. of con- centrated hydrochloric acid and dilute to 200 c.c. with water. Set the funnel in the flask, and pour into it the acid from the graduated cylinder. In removing the funnel, be careful not to wet the neck of the flask with the acid. Coil up the magnesium wire so that it can be pushed into the neck of the flask, when the latter is held in an inclined position. The coil must be so large that the wire sticks in the neck of the flask and does not slide into the acid. Replace the stopper in the flask and insert the delivery tube into the mouth of the 2-liter bottle. Now, shake the flask slightly so as to bring the acid in contact from time to time with the metal. When the wire falls into the acid, place the body of the flask immediately in the water in the trough. This will tend to keep the acid cool, and prevent the heat of the reaction from raising the tempera- ture of the acid and causing the action to proceed too rapidly. When the magnesium has all disappeared, remove the delivery tube. b. Lower the bottle in the trough (adding water, if necessary) until, on looking horizontally, with the eye at the level of the water, the levels inside and outside are seen to be the same. Incline the bottle, if necessary, to accomplish this. While the bottle is in this position, cover the mouth with a glass plate (or insert a cork), and set the bottle with its contents erect upon the table. Read the temperature of the water (?). Ascertain also the height of the barometer (?). If there is not time to proceed with the operations directed below, the bottle and its contents may be set aside until the following period. c. The weight of this hydrogen is to be found, not by weighing it ourselves, but by measuring its volume, and using the fact that 22.4 liters of the dry hydrogen at and 760 mm. weigh 2.016 g. (seed). * A 1-liter bottle (or 1-1. graduated cylinder) if available is better, because about 0.9 g. of magnesium (or 1.8 g. of iron, piano-wire, or 0.7 g. of aluminium wire) and 8 c.c. of the acid diluted to 100 c.c. are then used and time is saved. VALENCE OF A METAL BY DISPLACEMENT 53 d. Use a graduated cylinder (500 c.c.) to fill the bottle once more to the top with water, noting carefully the volume of water required (?). The hydrogen was mixed with water vapor. Find the ten- sion of the aqueous vapor at the temperature recorded in a [Appendix I] (?) and subtract this from the barometric height (?) Reduce the volume of hydrogen, from the observed tempera- ture and barometric pressure as just corrected, to and 760 mm. (?). Calculate the weight of this hydrogen. 22.4 liters weigh 2.016 g. Weight of metal taken g. Volume of hydrogen obtained c.c. Temperature Barometric height mm. Tension of aqueous vapor mm. Pressure of hydrogen, corrected mm. Volume of hydrogen at and 760 mm. c.c. Weight of this hydrogen g. e. The atomic weight of magnesium is 24.32. State just what experimental fact this sentence represents (?). /. The weight of hydrogen found in d was that displaced by the weight of magnesium taken in a. Calculate from these data the weight of hydrogen which would be displaced by one atomic weight (24.32 g.) of magnesium (?). What is the nearest whole number of atomic weights of hydrogen (1.008 g.) contained in this weight of hydrogen? This whole number is the valence of magnesium. Mg therefore displaces xR. Supply the value you have found for x (?). g. How many formula weights of hydrochloric acid (HC1) are required to furnish this amount of hydrogen? Now make the complete equation, supplying the values you have found for x, y and z: Mg + 2/HC1 > MgCl 2 + zH. You did not measure the weight of C1 2 , or determine the value of z. What law of chemistry enables you to supply this value without measurement? 54 VALENCE OF A METAL BY DISPLACEMENT h. If hydrogen is univalent, what is the valence of oxygen in water (H 2 O)? Write the formula of magnesium oxide (?). j. If the formula of hydrogen sulphide is H 2 S, what is the formula of magnesium sulphide? SECOND METHOD Apparatus: Wide test-tube with 2-hole stopper to fit. Funnel. Pinch-clamp, rubber connection and glass tubing. Rubber de- livery tube. Iron stand, ring, and clamp. 1-liter bottle. Trough. Thermometer. Barometer. 500 c.c. graduated cylinder. Materials: Magnesium ribbon, or iron piano-wire, or aluminium wire, or zinc (C.P. gran.). Hydrochloric acid (pure, cone.). a. Take a piece of magnesium ribbon weighing about 0.9 g.* and determine (balance) its exact weight to the nearest centi- gram (?). Tabulate all data as shown under d (First Method). Fit a wide test-tube with a 2-hole stopper, straight tube reaching almost to the bottom, funnel, pinch-clamp, and short rubber connec- tion. Set this up as in Fig. 16, using the tri- angle on a ring to support the funnel, and a clamp to hold the test-tube. The L-tube must not project below the bottom of the stopper. Test for air-tightness (Ex. 7 d). Coil up the magnesium ribbon, place it in the test-tube, and replace the stopper, Through the funnel, fill the apparatus completely, from the tip of the delivery tube to the clamp below the funnel, with water. Close the clamp when the funnel has almost emptied itself. Invert the 1-liter bottle (or a 1-liter graduated cylinder), filled with water, on the support in the trough, and insert the delivery tube in the mouth of the bottle. * For a 2-liter bottle, take 1.8 g. of magnesium. For other metals (and 1-liter bottle) use iron (piano-wire, about 0.9 g.), aluminium (wire, about 0.7 g.), or zinc (pure, granulated, about 1 g.). If zinc is used, weigh the test-tube first empty and again with the zinc, getting the weight of the latter by difference: also coil the platinum wire and place it amongst the zinc (the glass rod need not be de- tached). FIG. 16 VALENCE OF A METAL BY DISPLACEMENT 55 Fill the funnel with pure, concentrated hydrochloric acid, and admit this to the test-tube, a little at a time, in such a way that a steady, rapid, but not violent action takes place. Re- plenish the funnel, if necessary, so that the funnel never becomes entirely empty. A good deal of the acid may be required at first (especially with other metals than magnesium), before sufficiently rapid action sets in. When the metal has all dis- appeared, drive all the gas over into the bottle by pouring water once more through the funnel (be careful that no air is carried in with the water). b toj. Follow the directions given under the First Method. THIRD METHOD (Easily applicable to magnesium only) Apparatus: Balance. 250 c.c. bottle. Trough (stone ware or enamelled). 50 c.c. graduated cylinder. Glass plate. Ther- mometer. Barometer. Materials: Magnesium ribbon. Hydrochloric acid (cone.). a. Weigh (balance) to the nearest centigram exactly 2 meters of magnesium ribbon (?). Calculate what length will weigh exactly 0.2 g. and cut off this length for use. Record all data as shown under d (First Method). Roll the ribbon into a spiral coil somewhat smaller than the inside diameter of the mouth of the 250 c.c. bottle. Place in the trough about 5 cm. depth of water. Measure into the bottle 30 c.c. of hydrochloric acid (cone.) and fill it up to the brim with water. Cover it with a glass plate and invert it in the trough, leaving the glass plate in the trough with the bottle inverted upon it. If any air gets into the bottle, lift out the bottle with the plate firmly pressed against the mouth, fill it up with water and try again. Place the spiral of magnesium ribbon in the trough and slip the mouth of the bottle over it, setting the bottle down firmly on the bottom of the trough. When the magnesium has all dis- appeared, slide the bottle back on to the glass plate. b to j. Follow the directions given under the First Method. 56 SALTS EXERCISE 38* SALTS Object: To prepare lists of the three ways of liberating elements and the six ways of preparing salts which have been met with during the preceding work. Apparatus: Test-tubes. Trip scales. Watch glass. Becker. Materials: Magnesium ribbon. Sulphuric acid (dil.). Sodium carbonate. Calcium chloride. a. Put 5 cm. of magnesium ribbon in dilute sulphuric acid in a test-tube (?). What is the gas given off? What other product is formed and how should you obtain it in solid form? Write the equation, assuming Mg to be bivalent (?). Write an ionic equation also (?). Which of the varieties of chemical change is here illustrated? Give two other ways of liberating an element, with one illus- tration of each (?). b. Place 2 g. of sodium carbonate in one test-tube and 1 g. of calcium chloride in another. Dissolve each salt in 10 c.c. of water. Heat the calcium chloride solution to boiling and add to it a little sodium carbonate solution (?). Shake, wait until the precipitate has settled, and add one more drop of the sodium carbonate solution. Continue the three operations described in the last sentence until the last drop produces no further pre- cipitation in the clear part of the liquid. Then filter the mixture and evaporate two or three drops of the clear filtrate in a watch glass as in Ex. 10/(?). Write the formulae of the two salts taken (?). Separate the radicals in brackets thus (NH 4 ) (N0 3 ). Complete the equation as a double decomposition (?). Write the names under the formulae of the products (?). Write the equation in ionic form also (?). Define each of the two ways of forming salts which are illus- trated in this experiment (?). Define a third way used in Ex. 23 e, f. What have these three ways in common? Define a fourth way met with in Ex. 38 a (?). Define a fifth way which was illustrated in Ex. 5 d t Ex. 16 (?). Define a sixth way illus- trated in Ex. 6 c. * Exercises 38 and 39 are placed here as part of the review follow- ing Chap. XVIII. If more convenient, they may precede Ex. 25. HYDROGEN PEROXIDE 57 EXERCISE 39 CHEMICAL EQUILIBRIUM IN DOUBLE DECOMPOSITION Object: To study a reversible action, to show that it is incomplete, and to try one of the ways of carrying such a reaction to completion. [Read 235.] Apparatus: Test-tubes. Materials: Ammonium thiocyanate. Ferric chloride. a. When solutions of two substances, each composed of two radicals, are mixed, and no precipitate is observed, interaction nevertheless occurs [174]. Place 10 c.c. of water in each of two test-tubes, add to one a single drop of ammonium thiocyanate solution, and to the other a single drop of ferric chloride solution. Now mix the solutions (?). The radicals are (NH 4 )(CNS) and (Fe)(Cl),. Write the equation for the action which may be assumed to have occurred. Is there any evidence that interaction has taken place? Which of the four is the colored substance? Use the mixture for b. b. When no precipitate is formed, is an action like the above complete? To answer this question, divide the mixture from a equally between four test-tubes. Keep one for reference. To the second add one drop of ferric chloride solution (?), and to the third a drop of ammonium thiocyanate solution (?). In- terpret the result. Now add to the fourth tube a few drops of ammonium chloride solution (?) and explain. What other action have we shown to be reversible [127]? All double decompositions of substances composed of radicals are reversible, like these two. They are also often far from com- plete, when, as in the present instance, precipitation does not occur. Why does precipitation tend to make the action more nearly complete? EXERCISE 40 HYDROGEN PEROXIDE Object: To prepare a solution of hydrogen per oxide , to observe its properties, and to try a delicate test for its presence. Apparatus: Glass rod. Flask. Test-tubes. Funnel 58 HYDROGEN PEROXIDE Materials: Sodium peroxide (powdered). Litmus papers. Sul- phuric acid (dil.). Manganese dioxide. Splints. Lead nitrate (sol.). Ammonium sulphide (sol.). Filter paper. Potassium dichromate (sol.). Ether. a. To prepare a solution of hydrogen peroxide, take 100 c.c. of cold water in a flask, and about 1 c.c. of pulverized sodium peroxide on a piece of paper. Add the peroxide to the water, a very little at a time, shaking and cooling the mixture in running water during the process. Test a drop of the solution on litmus papers (?). Now, while still shaking and cooling in the same way, add dilute sulphuric acid a few drops at a time, until the mixture is acid. Write the equation (?). What does the solution now contain? b. Take 15-20 c.c. of the solution in a test-tube, and place about 1 c.c. of pulverized manganese dioxide on a piece of paper. Light a wooden splint, throw the manganese dioxide into the solution (?), and test the gas in the tube for oxygen (?). Write the equation (?). The manganese dioxide (catalyst) is un- changed. Is hydrogen peroxide stable or not? c. Take 2 drops of lead nitrate solution Pb(N0 3 )2, dilute with 5 c.c. of water and add 2 drops of ammonium sulphide solution (NH 4 ) 2 S (?). Pour the mixture on to a filter. The precipitate is lead sulphide, formed by double decomposition. Write the equation (?). Wash the precipitate and whole filter paper with water and, when the water has run through, wash once more. Then pour upon the precipitate some of the hy- drogen peroxide solution [222] (?). Write the equation (?). To what class of substances does hydrogen peroxide here show itself to belong? d. Test for Hydrogen Peroxide. Take about 1 c.c. of potas- sium dichromate solution and, to liberate dichromic acid, add an equal volume of dilute sulphuric acid. Take now a portion of the hydrogen peroxide solution, add 2-3 c.c. of ether, close with the thumb and shake. Then add to it one drop of the solution containing dichromic acid and shake again [223] (?). e. Summarize the observed properties of hydrogen peroxide: color (?), solubility (?), stability (?), oxidizing or reducing action (?), test (?). FORMS OF SULPHUR 59 EXERCISE 41 HYPOCHLOROUS ACID. BLEACHING Object: To find out how the commonest "bleach" does its work, and what kind of substances it bleaches. Apparatus: 90 c.c. generating bottle, 2-hole stopper, thistle, L-, and delivery tubes. Funnel. Test-tubes. Materials : Bleaching powder. Filter paper. Marble (chips) . Litmus papers. Colored calico (small strips). Hydrochloric acid (dil.). a. Take about 2 c.c. of bleaching powder with 20 c.c. of water in a test-tube, shake from time to time and finally filter to obtain a clear solution. Meanwhile arrange an apparatus to generate carbon dioxide as in Ex. 59 a. Pour most of the clear bleaching powder solution into another test-tube, and pass carbon dioxide through it for 5 minutes. The precipitate is calcium carbonate CaC0 3 . Filter again, to obtain a clear solution of hypochlorous acid [226] for use in c. b. In the rest of the bleaching powder solution dip strips of litmus paper. Leave one in the solution (?). Does bleaching powder solution bleach? Hang the other in the air (?). What acid here liberates the hypochlorous acid? To what class of chemical actions does that on the litmus belong? c. In the hypochlorous acid solution from a place small pieces of (1) litmus paper, (2) paper with printing on it [356], (3) paper with writing in ink [499] and (4) in pencil [330], and (5) colored calico. Observe and record the effect on each (?). Which of these owe their color or blackness to free carbon, and which to colored organic compounds? Does hypochlorous acid oxidize free carbon? What does it oxidize? EXERCISE 42 FORMS OF SULPHUR Object: To study a substance which shows two solid forms and two liquid forms. Apparatus: Test-tubes. Mortar. Watch glass. Lens (1 for 10 pupils). Trough. Funnel. Materials: Sulphur (roll). Carbon disulphide. Filter paper. a. Rhombic Sulphur. Place about 0.5 c.c. of powdered roll sulphur in a dry test-tube, add 2 c.c. of carbon disulphide and 60 FORMS OF SULPHUR shake (?). Pour the solution into a watch glass and set it to evaporate away from all flames. Examine the crystals with the eye and with a lens and make a drawing of two of them (?). Are they brittle or soft? Color? Are they transparent? After 24 hours (or more), are they still transparent? b. Monoclinic Sulphur. Fold a filter paper as if for filtration, and put water in the trough. Half fill a dry test-tube with roll sulphur. Hold the test-tube with the clamp from the iron stand and melt the sulphur. Heat gently, turning the tube in the flame. Dark brown patches show overheating at these points melted sulphur is pale straw-color. Hold the filter paper by the edge at the three-fold side and pour the melted sulphur into it. Watch the crystals grow. When crystals have formed at the surface and reached the center, pour the remaining liquid sulphur promptly into the trough of water, and open up the paper immediately. Examine the crystals with the eye and with the lens and make a drawing of two of them (?). Are they brittle or soft? Color? Are they transparent? After 24 hours (or more), are they still transparent? If not, into what form of sulphur have they turned? Examine the part that was poured into water. Is it brittle or soft? Dry a small piece of it and shake it with 1 c.c. of car- bon disulphide (?). c. Amorphous Sulphur. Half fill the same test-tube with roll sulphur and melt. Continue heating until the sulphur boils and note the changes in color and fluidity which occur (?). If the vapor catches fire, allow it to burn. Pour the boiling sulphur into the trough of water, moving the tube about. Examine the product. Is it crystalline? Is it brittle or soft? Is it transparent? After 24 hours (or more) is it still trans- parent? After 24 hours (or more), dry a part of it and shake with a little carbon disulphide (?). To find out whether any has dissolved, pour part of the liquid on to a filter, catch a few drops of the filtrate on a watch glass, and allow them to evapo- rate (?). What is the insoluble material? Color? Examine with a lens (?). Is it crystalline? HYDROGEN SULPHIDE 61 EXERCISE 43 SULPHIDES OF METALS Object: To observe the activity of sulphur towards metals. Apparatus: Test-tubes. Mortar. Materials: Sulphur (roll). Copper foil (strips). Iron (powder). Mercury (dropper in bottle). a. Place about 2 c.c. of roll sulphur in a dry test-tube and fasten the tube upright in the clamp on the stand. Boil the sulphur and then drop into the tube a strip of copper foil (?). Does the temperature of the copper change noticeably? Was it heated thus by the flame, the sulphur vapor, or what? Remove the strip of copper and describe the properties of the product (?). Name it (?) and write the equation (?). b. Mix thoroughly 1 c.c. of iron powder with 1.5 c.c. of powdered roll sulphur. Place the mixture in a test-tube and clamp the latter on the stand. Heat the lower part of the material and, when the reaction begins, withdraw the flame. Was the temperature at any time higher than that which the flame could have produced? What was the source of the heat? Describe the product when cold (?). Name it (?), and write the equation (?). Keep it for use in Ex. 44 e. c. With a dropper place a single globule of mercury in the mortar. Add an equal volume of sulphur and rub the two for several minutes, or until no mercury is visible (?). Under the same conditions (pressure, temperature, contact), does mercury combine more or less readily with sulphur than with oxygen? Give reasons for your answer (?). Does sulphur appear to have about the same activity as oxy- gen, or much more or much less? EXERCISE 44 HYDROGEN SULPHIDE Object: To prepare hydrogen sulphide. To study its physical and chemical properties, and to consider uses for them. Apparatus: Test-tube with 1-hole stopper, L-tube, and rubber tubing. Wide-mouth bottle and glass plate. 62 HYDROGEN SULPHIDE Materials: Ferrous sulphide (small lumps). Hydrochloric acid (da.)- Litmus papers. Cupric sulphate (sol.). Arsenious chloride* (sol.). Lead nitrate (sol). Antimony trichloride (sol.). a. Take a test-tube fitted with a 1-hole stopper, L-tube, and rubber tube ending in a straight glass tube. Hold the test-tube almost horizontal and slip into it carefully about 3 c.c. of ferrous sulphide. Add dilute hydrochloric acid and replace the stopper. Note the color (?) and odor (?) of the gas. Avoid breathing it, however, as far as possible. b. Fill a bottle with the gas by upward displacement of the air and cover the bottle with a glass plate. Set fire to the gas at the end of the delivery tube. Odor? What products are formed? Place the delivery tube in a test- tube half filled with water, so that it reaches the bottom and let the gas bubble through the water for several minutes. Use the solution in c. Now set fire to the gas in the bottle (?). What products are formed when the gas burns in a bottle? Why is the result different from that when a jet of the gas burned in the air? When the solution has been made, pour water into the gen- erating tube and wash it out. Put solid matter in the jar not in the sink. c. Smell the solution made in b (?) and test it with litmus paper (?). To what class of substances does hydrogen sulphide belong? What other name is given to the solution? Take 4 test-tubes and in each place about 2 c.c. of a solution of a different one of the following salts: (1) Cupric sulphate, (2) Arsenious chloride AsCl 3 , (3) Lead nitrate Pb(N0 3 ) 2 , (4) Anti- mony trichloride SbCl 3 . Add a part of the solution of the gas to each (?). What variety of chemical change will an acid and a salt undergo in solution [173]? Make equations for the four actions accordingly (?). d. Summarize the observed properties of hydrogen sulphide (?). How could you identify hydrogen sulphide? How could you use it in identifying the metallic radicals in different salts? e. To the residue from Ex. 43 b, add dilute sulphuric acid. Identify the gas liberated, using at least three different proper- ties, and record the results (?). * Dissolve arsenic trioxide in dilute hydrochloric acid. SULPHUR DIOXIDE 63 EXERCISE 45 SULPHUR DIOXIDE Object: To prepare sulphur dioxide and to study its properties. Apparatus : Watch-glass. Platinum wire. Wide test-tube, 2-hole stopper, funnel, pinchclamp, rubber and glass tubing. Test- tubes.. Wide-mouth bottle, glass plate and cork. Trough. Materials: Sulphur. Sodium bisulphite. Hydrochloric acid (dil.). Pinks or grass or leaves. Apple. a. Place on a watch-glass a particle of sulphur and touch it with a warm platinum wire. Bring the wire with the ad- her ing sulphur again into the flame. Withdraw and note the color (?) of the flame of burning sulphur and the odor (?) of the gas produced. Name the gas that has this odor (?) , and write the equation (?). ~ 3 - : ^ b. Fit up an apparatus as in Fig. 16 (Ex. 37). Place in the test- tube about 10 c.c. of sodium bisulphite, and attach a straight glass tube reaching down to the bottom of an upright, dry test- tube. Put dilute hydrochloric acid in the funnel, and admit it drop by drop to the apparatus. If there is little evidence of action (bubbling), the apparatus may be warmed very slightly to start the reaction. Put water in the trough. Also have ready a bottle contain- ing a moist pink (or some grass or leaves) and half a slice of an apple. Leave the other half-slice exposed to the air for com- parison later. Likewise boil half a test-tube full of water for 2 minutes and set aside to cool. c. Now transfer the delivery tube to the bottle, and close the mouth of the test-tube firmly with the thumb. Pour quickly a little water into the test-tube and close again firmly. Still keeping the thumb in position, place the mouth of the test- tube under the water in the trough. Notice the level of the water in the test-tube and then remove the thumb (?). In- ference (?). d. Cool the boiled water in the test-tube, and again transfer the delivery tube, inserting it to the bottom of boiled water, and let the gas run in for 5 minutes. Cork this tube the instant the delivery tube is taken out, so as to enclose the gas, and not admit air. Keep this solution for Ex. 46. 64 SULPHUROUS ACID Cover the bottle or, better still, cork it. After 5 minutes, pass more of the gas into the bottle, and finally cork it again. Observe the color of the contents from time to time (?). Compare the pieces of apple after both have been exposed to the air for a day or more (?). e. Summarize the properties of sulphur dioxide: color (?), odor (?), density compared with air [259] (?), solubility (?), action on vegetable coloring matters (?). jju^^v^^ EXERCISE 46 SULPHUROUS ACID Object: To learn the properties of sulphurous acid. Apparatus : Evaporating dish. Test-tubes. Mortar. Materials: Sulphurous acid (from Ex. 45 d). Litmus papers. Barium chloride (sol.). Iodine. a. Use the solution made in Ex. 45 d. Test with litmus papers (?). What sort of substance has been formed? Is sulphur dioxide an acidic or a basic oxide [259]? b. Pour a part of the solution into an evaporating dish, set it on the wire gauze, and boil it [HOOD], noting the odor from time to time (?). Is sulphurous acid stable? c. To half of the rest of the solution add one or two drops of barium chloride solution (?). Disregard any very slight cloudi- ness. To the other half add a couple of crystals of iodine (pul- verized in the mortar), shake until the iodine has dissolved, and then add barium chloride solution (?). The precipitate is barium sulphate BaS0 4 , and its formation shows that the radical S0 3 has become S0 4 . Which substance was here oxidized? What substance was reduced? Write equations for the action of iodine (?), and the subsequent action of barium chloride (?). d. Summarize the properties of sulphurous acid: color (?), odor (?), stability (?), oxidizing or reducing agent (?). If the water for the solution had not been boiled, what would have happened [34, par. 2]? How should you prepare a solution of sodium sulphite from sulphurous acid? , *" 7W~? Jwbl*~ raer &- - yi**esAty~'** ^ c f Kfti & 6' -<;// ' SULPHURIC ACID 65 EXERCISE 47 SULPHURIC ACID Object : To learn the properties of pure and of diluted sulphuric acid, and to try a test for the sulphate ion. Apparatus: Test-tubes. Glass rod. Evaporating dish. Materials: Sulphuric acid (cone.). Litmus papers. Barium chloride (sol.). Hydrochloric acid (cone.). Sodium sulphate. Copper (shavings). a. Take 5 c.c. of water and pour into it about 1 c.c. of con- centrated sulphuric acid [CAUTION. Never pour the water into the acid]. Touch the back of the hand with the bottom of the test-tube (?). b. Apply the solution with a glass rod to litmus papers (?). c. Boil nearly all the rest of the solution gently in an evaporat- ing dish with a small flame and note whether there is any odor. After five minutes, test again with litmus papers (?). Is the acid like sulphurous acid, or is it more stable (?)? Let the dish cool before washing it out. d. Test for the Sulphate Ion SO 4 = . To the remainder of the solution add barium chloride solution (?). Add now 1 c.c. of concentrated hydrochloric or nitric acid (?). Other common salts of barium, if precipitated, would be decomposed and dis- solved by these acids. Write the equation (?). Repeat the test, using a few particles of sodium sulphate or ammonium sulphate dissolved in water (?). Write the equa- tion (?). e. Twist a few copper shavings into a ball and place them in a test-tube. Add 1 c.c. of concentrated sulphuric acid. Heat gently with a small flame. Note how long it takes to make the acid hot enough to interact at all [CARE! Hot sul- phuric acid, if spilled, may produce severe burns]. Note the odor (?). Test to see whether any hydrogen is produced (?). Has the sulphuric acid been reduced? What sort of substance is hot concentrated sulphuric acid? /. Summarize the properties of the acid: State (?), color (?), odor (?), stability (?), action on litmus (?), action on water (?), on barium chloride (?), on elements like copper (?). 66 PERCENTAGE OF OXYGEN IN AIR EXERCISE 48 PERCENTAGE OF OXYGEN IN Am Object: To find the volume of oxygen contained in a definite volume of air by absorbing the oxygen out of this air and measuring the shrinkage. Apparatus: See Fig. 17. One hole in the cork (better than rubber stopper, because latter tends to slip out when wet with the alkali) is plugged with a bit of glass rod with fire-polished ends. The lower end of the short glass tube is previously heated until the opening shrinks to half its original diameter. Graduated cyl- inder. Materials: Potassium pyrogallate (alkaline sol.*). Rubber bands. Taper. a. Before attaching the funnel, test the apparatus (Fig. 17) for air-tightness. Remove the test-tube, temporarily, and take the glass rod out of the cork. Pour about 40 c.c. of the potassium pyrogallate solution into the funnel. The following operations must be done quickly as the solution gradually absorbs oxygen from the air of the room and becomes useless. Do not get the solution on the hands, as it stains the skin. Open the pinchclamp and permit the liquid to fill the rubber tube and the glass tube com- pletely down to the opening of the nozzle. Replace the test-tube, fitting -the cork tightly into its mouth. Finally, close the hole in the cork with the glass rod, thus enclosing a volume of air equal to the capacity of the test-tube. Now, open the pinchclamp. A few drops of the solution will run into the test-tube and, as the oxygen is absorbed, more will follow. Close the clamp and turn the test-tube upside down once or twice to bring the liquid near every part of the oxygen. In doing this, hold the test-tube with a folded strip of paper * For 20 students, dissolve 200 g. of potassium hydroxide and 20 g. pyrogallic acid in 1 liter water immediately before use and keep tightly stoppered. FIG. 17 CARBON DIOXIDE IN AIR 67 (Fig. 1, Ex. 1 a), and not with the bare hands, since this would warm the gas and render the result inaccurate. Then hold the clamp open, invert the test-tube and hold it so that the levels of the liquid in it and in the funnel are the same, and close the clamp. Restore the test-tube to its original position and place on it two rubber bands to mark the levels of the lower end of the stopper and the surface of the liquid. Light a taper, disconnect the test-tube, and plunge the flame into it (?). Without disturbing the bands, wash the test-tube out. By means of a graduated cylinder, measure and record the volumes of water required to fill the test-tube up to the lower (?) and to the upper (?) bands. The former is the volume of the oxygen, the latter that of the air. Calculate the percentage of oxygen by volume in air as follows: volume of oxygen X 100 ; r : = x = % oxygen. volume of air What gases were left, after the oxygen had been absorbed? What properties of nitrogen did you observe? EXERCISE 49 CARBON DIOXIDE IN AIR AND IN THE BREATH Object: To show the presence of carbon dioxide in atmospheric air and in expired air. Apparatus: Beaker. Glass tube. Test-tube. 2 wide-mouth bottles and glass plates. Trough. Materials: Barium hydroxide (sol). Taper. Lime water. a. Place about 3 c.c. of clear barium hydroxide solution in the bottom of a clean beaker and leave it exposed to the air for half an hour or more (?). Barium hydroxide Ba(OH) 2 behaves towards carbon dioxide like limewater, but, being more soluble than calcium hydroxide, its solution is more concentrated and a more copious precipitate can be obtained. Explain the result (?), and write the equation for the action (?). 6. Blow air from the lungs through a straight tube into 5 c.c. of limewater (?). c. Fill two bottles with water and invert them in the trough. 68 AMMONIA By means of a tube, fill one with air from the lungs immediately after drawing a breath. Fill the other with air after the lungs have been almost emptied. Slip a glass plate under each bottle and set both upright on the table. Light a taper and plunge it into one bottle (?) and then into the other (?). Explain the result (?). EXERCISE 50 AMMONIA Object: To study two ways of obtaining ammonia and to observe its physical and chemical properties. Apparatus: Test-tubes. 1-hole stopper, L-tube, and perforated cardboard. 2 wide-mouth bottles, and glass plates. Glass rod. Trough. Beaker. Cork. Materials: Gelatine (fine flakes). Litmus papers. Soda lime. Ammonium chloride. Slaked lime. Ammonium sulphate. Hydrochloric acid (cone.). a. From Organic Matter. Take 0.5 c.c. of gelatine in a dry test-tube. Place moistened litmus papers (blue and red) in the mouth of the tube and heat gently. Note the odor (?) and effect on litmus (?). Insert a glass rod wet with concentrated hydro- chloric acid (?). Repeat, first mixing on paper the gelatine with an equal amount of soda lime (?). Almost all organic compounds con- taining nitrogen give ammonia when heated with soda lime, and this is therefore a test for such compounds. b. From an Ammonium Salt. Place a little ammonium chloride in the palm of one hand, a little slaked lime in the other, and rub the two together. Note the odor (?) and effect on mois- * tened litmus paper held over the mixture (?). Repeat, using ammonium sulphate and slaked lime (?). c. Take one-fourth of a test-tube full of am- ^ monium chloride and mix it on paper with an ^ j g equal volume of slaked lime. Place it in a test- tube provided with a one-hole stopper and L-tube long enough to reach the bottom of the inverted bottle (Fig. 18). Clamp AMMONIA 69 the tube so that the mouth is inclined very slightly down- wards (to prevent condensed moisture running back). Arrange the perforated card on a ring, and first slip an inverted test- tube over the L-tube. Provide a test-tube containing a few drops of concentrated hydrochloric acid. Also, place water in the trough. Warm the mixture very gently with a small flame. Dip the end of a thin glass rod in the hydrochloric acid, and bring it close to the perforation in the card to ascertain when the test- tube is filled with the gas. Dense smoke will notify you of this condition. Remove the test-tube, closing it firmly with the thumb, and with the other hand set a bottle (to be used in e) over the L-tube. d. Place the mouth of the test-tube under water and remove the thumb (?). Is the gas soluble in water? How does its behavior compare with that of chlorine (Ex. 21 a) in this respect? e. Warm a second bottle by moving it rapidly through the flame. Do not let it rest in the flame or it will crack. Place in the bottle 3 drops of concentrated hydrochloric acid, cover it with a glass plate, and turn it so as to spread the acid as com- pletely over the inner surface as possible. Now, ascertain by use of the rod dipped, in hydrochloric acid whether the first bottle (c) is full of ammonia. When it is, raise it off the tube, slip a glass plate under the mouth, and set the bottle mouth downwards on the table ready to be used in g. f. Swing the L-tube downwards so that its free end is just above (but not touching!) the surface of the 5 c.c. of water in the bottom of a beaker. At the end of 5 minutes pour the solution into a test-tube, cork it up, and reserve for use in Ex. 49. During the five minutes proceed with g, but swing the water round hi the beaker occasionally to submerge the surface layer. Concentrated ammonia has a density of 0.88, i.e., 1 c.c. weighs 0.88 g. Will the solution float or sink? What difference would it make if the beaker were left at rest? g. Bring the two bottles from e mouth to mouth and remove both plates. Invert the pair of bottles once or twice to mix the gases (?). What is the deposit? Describe its physical proper- ties (?). Write the equation for the action (?). h. Summarize the observed properties of ammonia (?). T 70 HYDROXIDE AND SALTS OF AMMONIUM EXERCISE 51 HYDROXIDE AND SALTS OF AMMONIUM Object: To observe the properties of ammonium hydroxide and of salts of ammonium, and to learn a test for the latter. Apparatus: Glass rod. Evaporating dish. Beaker. Test-tubes. Materials: Litmus papers. Hydrochloric acid (dil.). Ammonium chloride. Sodium hydroxide (sol.). Ammonium sulphate. a. Ammonium Hydroxide. Dip a rod in the solution made in Ex. 50 / and touch litmus papers with it (?). To what class of substances does the material in solution belong? Write the equation for the formation of this material (?). b. Pour a part of the solution into an evaporating dish and boil it. From time to time observe its odor and reaction towards litmus papers (?), proceeding meanwhile with c. What must have happened to the compound in the solution? Is it a stable or an unstable compound [304]? Write the equation (?). Is this action a reversible one or not? Is it complete? c. Place the rest of the solution in a beaker, add dilute hydro- chloric acid a little at a time, stirring with a rod and testing the liquid on litmus papers until the liquid is neutral. Evaporate the liquid in a dish almost (but not quite) to dryness (lower the flame towards the end), allow it to cool and describe the residue (?). Write the equation (?). d. Summarize the properties of ammonium hydroxide (?) e. Ammonium Salts. Place not over 0.2 c.c. of ammonium chloride in the bottom of a dry hard glass test-tube. Clamp the latter in a horizontal position, and place in the mouth of the tube moistened litmus papers (red and blue). Heat the salt and watch the test papers for any changes and describe them (?). Is there evidence that the salt decomposed? What were presumably the products? Make the equation (?). Would these products recombine (partially at least) in the cool part of the tube (Ex. 50 #)? I s there any sublimate vMble (?) and if so, what is it? What would be the final effect of continuing the heating of the salt? /. Test for Salts of Ammonium. Take 2 c.c. of sodium hy- droxide solution and add a few particles of any salt of ammonium (e.g., the sulphate). Warm, and observe the odor (?). NITRIC ACID 71 Write the equation as a double decomposition (?). Which of the products decomposes to give the ammonia? EXERCISE 52 NITRIC ACID Object: To prepare nitric acid, to study its properties, and iff 'ry to test for a nitrate. Apparatus: Tubulated retort (glass stopper). Flask. Trough. Funnel. Porcelain crucible. Materials: Sodium nitrate. Sulphuric acid (cone.). Charcoal (splinters). Woolen yarn (white). Copper (shavings). Splints. Zinc (gran.). Ferrous sulphate (sol.). a. Put about 20 g. of sodium nitrate in a tubulated retort. Insert the neck of the retort into the mouth of a flask (Fig. 19). Clamp the tubulus (mouth) of the retort so that the body rests on the wire gauze and the flask is partly immersed in a vessel of cold water. Through a funnel or thistle tube pour about 15 c.c. of concentrated sulphuric acid upon FIG. 19 the sodium nitrate, place the stopper in the tubulus of the retort, and wait until the acid has moistened the entire mass. Caution: Sulphuric acid and nitric acid both produce severe wounds on the flesh and destroy clothing. The nitric acid to be prepared is 100%, and the greatest care must be used in handling it. Heat the retort very gently [HOOD], and distil at as low a tem- perature as possible until no more nitric acid condenses in the neck of the retort (meantime, proceed with d). Allow the retort to cool before touching it. What is the brown gas seen in the retort (?), and whence does it come [309]? What is the residue in the retort? 6. Pour part of the distillate (nitric acid) into the porcelain crucible. Does its vapor produce a fog with moist air (breath)? Twist an iron wire round a splinter of charcoal, set fire to the latter, and dip the brightly glowing charcoal into the acid (?). 72 NITRIC OXIDE This shows its oxidizing power. What compound of carbon is probably formed? c. Divide the rest of the distillate between four dry test- tubes. In one place a piece of white woolen yarn (?), in the second a small piece of copper (?), in the third a piece of a splint (?), and in the fourth a small piece of zinc (?). The action on copper is a test for nitric acid, by itself, or mixed with other substances. What gas does zinc displace from other acids? What gas is produced, with zinc, here? d. Test for the (NO 3 ) radical (follow the directions with care). Pour into a test-tube 3 c.c. of ferrous sulphate solution. Add to it 2 drops of dilute nitric acid and shake. Incline the tube very slightly, and pour concentrated sulphuric acid (not over 2 c.c.) in a steady stream down the wall of the test-tube so that (being a heavy liquid) it flows to the bottom and collects below the ferrous sulphate solution (?). Describe the coloration in the layer where the liquids meet (?). Repeat the test, adding a small crystal of sodium nitrate, instead of the nitric acid, and shaking. How should you recognize an unknown substance to be a nitrate? e. Summarize the properties of nitric acid (?). * EXERCISE 53 NITRIC OXIDE Object: To observe the action of dilute nitric acid on copper. To prepare nitric oxide and study its properties. To observe part of the process used in the fixation of atmospheric nitrogen. Apparatus: Gas generating bottle (90 c.c.), 2-hole stopper, thistle, L-, and delivery tubes. Trough. Wide-mouth bottle. Gradu- ated cylinder. Test-tubes. Deflagrating spoon. Glass plate. Wide test-tube, 2-hole stopper, dropper, L- and delivery tubes. Materials: Copper (shavings or clippings). Nitric acid (cone.). Asbestos paper. Taper. Phosphorus (red). Sodium per- oxide. Litmus papers. a. Fit up a generating bottle as in Fig. 10 (Ex. 10 a). Place in it copper shavings or clippings. Invert one bottle, one test- J ' s V NITRIC OXIDE 73 tube, and the graduated cylinder, all full of water, in the trough. Pour some water through the thistle tube, and an equal volume of concentrated nitric acid and wait for the action to start. Then fill the bottle and test-tube with the gas, collect about 30-50 c.c. (only) of the gas in the graduated cylinder, and leave them stand- ing in the trough. Note the color of the gas in the generator just after the be- ginning of the action (?) and again later (?). Note also the color of the liquid in the generator. This is characteristic of cupric salts, and is the color of the cupric-ion Cu++ b. What is the color of the gas? Use the test-tube full of the gas to test its solubility in water as in Ex. 45 c (?). What happens when the test-tube is opened to the air (this action is examined further in d)l c. Line the deflagrating spoon with asbestos paper and place in it a little red phosphorus. Cover the bottle full of the gas with a glass plate, and set it upright on the table. Plunge a burning taper into the gas (?), withdraw it instantly, and cover the bottle. Set fire to the phosphorus, and when it is burning vigorously, plunge it into the same bottle (?). Heat the spoon and asbestos paper, to burn the adhering phosphorus, before putting the spoon away. d. Fit a wide test-tube with a 2-hole stopper, L-tube and rubber delivery tube, and a dropper (Fig. 20). Place in the test-tube about 1 c.c. of sodium peroxide. Fill the dropper with water, and immerse the delivery tube in the trough. Pinch the dropper cautiously so as to allow one drop of water at a time to fall on the peroxide. When the air has been displaced from the test- tube, read the volume of the gas in the graduated cylinder (?), and allow the oxygen to ascend, a few bubbles at a time, into the latter (?). Note the change in color (?). Slightly shake the water in the cylinder to bring it in contact with the gas. Does the volume change (?) and, if so, in which direction? Re- member that oxygen gas is being added. Finally, close the cylinder with a glass plate, set it upright, and test the water in it with blue litmus paper (?). 20 74 NITROUS OXIDE e. Which component of the air caused the nitric oxide to become brown in 6? What is the brown gas? What property of the brown gas have you learned in dl What reaction to lit- mus had the water in the cylinder (?) and what was the sub- stance formed [312]? What great industrial process is based on this reaction [313-4]? /. Summarize the properties of nitric oxide (?). EXERCISE 54 NITROUS OXIDE Object: To prepare nitrous oxide and to study its properties. Apparatus: Test-tube, 1-hole stopper, L- and delivery tubes. Test-tubes. Wide-mouth bottle. Trough. Deflagrating spoon. Materials: Ammonium nitrate. Splints. Asbestos paper. Sul- phur. a. Preparation of Nitrous Oxide. In a large test-tube pro- vided with a 1-hole stopper and rubber and glass delivery tube, place 10 g. of ammonium nitrate. Clamp the test-tube at an angle of 45. Fill one bottle and two test-tubes with water and invert them in the trough (use warm water, if available). Heat the nitrate cautiously but continuously with a small flame, and allow the gas to come very slowly. If, before the vessels are filled with gas, the nitrate threatens to give out [explosion possible], first remove the delivery tube from the trough, then stop heating, and add more ammonium nitrate. Watch the water in the delivery tube. Does anything else appear to be produced along with the nitrous oxide gas? What is it? 6. Use one test-tube of the gas, as in Ex. 45 c, to find out whether the gas is soluble in cold water (?). Does the gas differ from oxygen in this respect? c. Into the second test-tube thrust a glowing splinter (?). Does the gas differ from oxygen in this respect? d. Line the deflagrating spoon with asbestos paper and place on it a little sulphur. Set fire to the sulphur, without heating the spoon. Immediately, while it is still burning feebly, thrust it into the bottle of the gas (?), and then remove it and cover the bottle. Heat the spoon until the sulphur burns briskly and PHOSPHINE AND PHOSPHORIC ACID 75 thrust it into the bottle once more (?). How does the gas differ in behavior from oxygen? Note the odor in the bottle (?). What is formed when sul- phur is burned in nitrous oxide? ' e. Summarize the properties of nitrous oxide: color (?), solubility (?), density compared with air (?), supports com- bustion, how well (?). /. Name two respects in which nitrous oxide differs from oxygen (?). When nitrous oxide is added to nitric oxide, no brown gas (Ex. 53 d) is formed: this is another difference. EXERCISE 55 PHOSPHINE AND PHOSPHORIC ACID Object: To prepare phosphine and to observe the reactions of phos- phoric acid or phosphates. Apparatus: Test-tubes. Glass-tubing. Mortar. Dropper. Materials: Calcium phosphide. Litmus papers. Phosphoric acid (sol.) or sodium phosphate. Ammonium molybdate (sol.*). Silver nitrate (sol.). Ammonium hydroxide (sol.). Nitric acid (cone.). a. Phosphine. Drop a small piece of calcium phosphide, Ca 3 P2, half the size of a pea, into 3 c.c. of water in a test-tube (?) . The gas is phosphine PH 3 . Try the reaction of the gas (not the liquid) with moist litmus papers (?). What reaction would ammonia NHa gas give? Note the odor (?). Is the gas com- bustible? Is 1 its kindling temperature low or high? Test the reaction of the water (?). What must the dissolved substance be? Write the equation for the action of the calcium phosphide on water (?). 6. Test for the Phosphate Radical. To 10 c.c. of water add not over 1 c.c. of phosphoric acid H 3 P0 4 (or 0.5 c.c. of sodium phosphate). Take 5 c.c. of ammonium molybdate solution, add to it 2 drops (not more, reserve the rest for c) of the phos- phoric acid solution and warm the mixture (?). This is a test for the radical of orthophosphoric acid (P0 4 ) and the phosphates. * 70 g. ammonium molybdate and 180 c.c. nitric acid to make 1 liter of solution. 76 ARSENIC TRIOXIDE c. To the rest of the phosphoric acid solution add silver nitrate solution, shaking and adding more until a permanent precipitate is formed (?). The precipitate is silver orthophosphate Ag 3 P0 4 . Write the equation (?). Like all double decompositions, this one is reversible, and is therefore incomplete. Name the interacting substances in the reverse action (?). To stop this reverse action, destroy the acid by adding ammonium hydroxide solution one drop at a time, noting the effect, shaking, and examining again. What evidence is there that the action now goes further forward? Finally, add concentrated nitric acid (?). Which way does the action now go? EXERCISE 56 ARSENIC TRIOXIDE Object: To observe the reduction of an oxide by carbon and to study the properties of arsenic trioxide. Apparatus : Glass tubing. Test-tubes. Materials: Arsenic trioxide. Charcoal (powdered). Hydrochloric acid (cone.). Sodium hydroxide (sol.). a. Draw out a piece of glass tubing to make two ignition tubes each 7 cm. long. Place in the closed end of one a very small amount of arsenic trioxide. Heat the oxide, and watch the cold part of the tube for a sublimate [324] (?). Is the oxide volatile? Does it melt before vaporizing? O^ 6. Place a small amount of arsenic trioxide in the other tube, and above it a little powdered charcoal. Heat the oxide and the charcoal, and examine the cold part of the tube [324] (?). What change has the oxide undergone? c. Take about 0.5 c.c. of arsenic trioxide in a test-tube, add 2 c.c. of water and warm (?). Now add 1 c.c. of concentrated hydrochloric acid and heat again (?). To what class of oxides does arsenic trioxide appear to belong? Write the equation (?). Set aside and examine later. Is the action reversible? d. Take about 0.5 c.c. of arsenic trioxide, add 2-3 c.c. of sodium hydroxide, and warm (?). To what class of oxides does it appear now to belong? GRAPHITE 77 EXERCISE 57 GRAPHITE Object: To try the action of solvents, and of solutions of acids and bases on graphite, to see whether it dissolves in the former, or in- teracts with the latter. Apparatus: Test-tubes. Materials: Graphite (powdered). Hydrochloric acid (dil.). Am- monium hydroxide (sol.). Carbon tetrachloride or disulphide. a. Place not over 0.2 c.c. of graphite in each of three test- tubes. Add 5 c.c. dilute hydrochloric acid, as an example of an acid, to one. Add 5 c.c. of ammonium hydroxide, chosen as a base, to the second. Add 4 c.c. of carbon tetrachloride, chosen as a solvent, to the third. Shake the last vigorously (away from all flames). Does the graphite dissolve? Name a solvent for carbon (?). b. Boil the two other samples with the acid and base, re- spectively. Is there any evidence of continued action, when the tube is taken out of the flame? Conclusion (?). What are the uses of graphite? EXERCISE 58 CARBON DIOXIDE BY OXIDATION Object: To observe the production of carbon dioxide when wood burns and oxides of metals are reduced by carbon. Apparatus: 250 c.c. bottle. Mortar. Trip scales. Hard glass test-tube with 1-hole stopper and L-tube. Materials: Limewater. Splints. Cupric oxide (powdered). Char- coal (powdered). Stannic oxide (powdered). Lead monoxide. a. Place 10 c.c. of limewater in a 250 c.c. bottle. Burn a splinter of wood in the bottle, taking care not to drop any ashes into the liquid. Close the bottle with the hand and shake (?). If the change is not distinct, repeat the burning, using the same limewater, and shake again. What elements does wood con- tain? Make the equations for the reactions of the carbon dioxide with the limewater. 6. Mix intimately in the mortar 5 g. of cupric oxide and 0.5 g. of powdered charcoal. Place this on a strip of paper, 78 CARBON DIOXIDE BY OXIDATION folded V-shape, and slip the hard-glass test-tube over the paper. Turn the tube round, so as to leave the mixture in it, and with- draw the paper. Insert the stopper and L-tube. Place 10 c.c of limewater in a test-tube. Clamp the tube containing the mixture in a horizontal position, at such a height that it can be heated, and let the L-tube project to the bottom of the lime- water. If the tube is too short to reach the bottom, add a straight glass tube and rubber connection. The purpose is to compel any gas which may be given off to bubble through the entire depth of the limewater. Heat the mixture, beginning at the end farthest from the stopper, at first gently and then strongly and persistently. What change takes place in the limewater? Finally, take the tube out of the limewater and then remove the flame. When the tube is cold, grind the contents in the mortar with water, and wash away the lighter particles. Examine the residue (?). Make the equation for the action (?). What important indus- trial processes depend on this reaction? What was oxidized and what reduced in this reaction? c. Perform the same experiment, using 5 g. of oxide of tin and 1 g. of charcoal. Answer the same questions as in a. d. Perform the same experiment, using 2 g. of litharge (lead monoxide) and 2 g. charcoal. In this instance heat gently. Answer the same questions as in a. EXERCISE 59 CAKBON DIOXIDE PKEPAEATION AND PROPERTIES Object: To prepare carbon dioxide and to observe its properties. Apparatus: Gas generating bottle (90 c.c.), 2-hole stopper, thistle tube, L-tube and rubber delivery tube. 3 wide-mouth bottles (250 c.c.) and glass plates. Test-tubes. Taper. Materials: Marble (chips). Hydrochloric acid (dil.). Litmus (sol . ) . Limewater. a. Use the apparatus in Fig. 10, Ex. 10 a. Slide into the bottle (do not drop them in) enough marble chips to fill it to a depth of one inch, and connect. Add dilute hydrochloric acid and fill all bottles with the gas by upward displacement of air. Cover the bottles with glass plates. To a test-tube (clean) full of water add some litmus solution. CARBON MONOXIDE 79 Pour half of the mixture into another test-tube and keep the latter for reference. Through a clean glass tube, pass carbon dioxide into the other half (see c). b. Light a taper and pour the gas from one of the bottles over the flame, as you would water (?). Does the gas support com- bustion? Is the gas heavier or lighter than air? Give the reason for your answer (?). To learn whether the gas is soluble in water, pour about 10 c.c. of water into a bottle of the gas, cover quickly and firmly with the palm of the hand, and shake vigorously. Is the hand held against the mouth of the bottle by atmospheric pressure, or not? Is the gas soluble? To ascertain whether the gas diffuses upwards, set the emptied bottle (now filled with air) over the full one, and mouth to mouth with it, and withdraw the plate. After ten minutes (meanwhile, do c), replace the glass plate between the bottles, remove the upper bottle, along with the plate, and set it upright upon the table. Slip the plate aside for a moment, add some limewater, replace the plate, and shake (?). Did the greater density of the carbon dioxide prevent its diffusing into, and displacing a part / of the air? c. Examine the litmus solutions, and compare their color (?). What property has the solution of carbon dioxide in water? How is the substance formed (equation)? d. Make a list of the properties observed: Color (?), odor (?), density (?), diffusibility (?), solubility (?), supports combustion or not (?), what chemical action on water (?). Note which of these properties are physical and which chemical (?). e. Why will any other acid act on marble as does hydrochloric acid [333]? If you obtained a carbonate as an unknown substance, how should you proceed to identify it? EXERCISE 60 CARBON MONOXIDE Object: To prepare carbon monoxide and to observe its properties. Apparatus: Flask (200 c.c.) with 2-hole stopper. Funnel, pinch- clamp, straight tube and rubber connection. L-tube and de^ livery tube. Trough. 3 wide-mouth bottles (250 c.c.), 3 glass 80 HYDROCARBONS Materials: Sulphuric acid (cone.). Formic acid. Limewater. Taper. Caution: The gas is poisonous (HOOD). Do not allow it un- necessarily to escape into the room. a. Fit a 200 c.c. flask with a 2-hole stopper, L-tube and rubber delivery tube, and the funnel and straight tube with pinchclamp shown in Fig. 16 (Ex. 37). Place the flask on the ring of the iron stand (with wire gauze), at a suitable height for heating by a small flame. Hold the funnel erect in the clamp. Extend the delivery tube, if necessary, by adding a bent glass tube so that the gas may be collected over water. Remove the stopper, pour into the flask about 1 cm. depth of concentrated sulphuric acid, and replace the stopper. Pour some formic acid into the funnel, and never allow this entirely to run out during the experiment. Warm the sulphuric acid gently (small flame), and then admit the formic acid a drop or two at a time. Collect three bottles full of the gas. What will the first bottle largely contain? Do not use this one. b. Light a taper, raise one bottle out of the water and plunge the taper up into it. Does the gas burn? Does the taper burn in the gas? c. Slide the glass plate, for a moment, partly off a second bottle of the gas and pour in a little limewater. Shake (?). Now light a taper, set fire to the gas in this bottle, replace the cover instantly, and shake again (?). What product is formed when carbon monoxide burns? Make the equation (?). d. Summarize the properties of carbon monoxide: color (?), solubility in water (?), burns or not (?), supports combustion or not (?). What is the density compared with that of air [340]? How could you distinguish burning hydrogen from burning carbon monoxide? EXERCISE 61 HYDROCARBONS Object: To make two typical hydrocarbons, to ascertain their proper- ties, and to compare the luminosities of their flames. Apparatus: Test-tube. 1-hole stopper and L-tube. 250 c.c. bottle. 12" rubber tube. Evaporating dish. Beaker. HYDROCARBONS 81 Materials: Soda lime. Sodium acetate. Limewater. t Litmus papers. Hydrochloric acid (cone.). Calcium carbide. a. Methane. Mix about 2 c.c. each of powdered soda lime and sodium acetate and place the mixture in a test-tube. Clamp this in a horizontal position and insert in it a 1-hole stopper with L-tube pointed upwards. Tap the test-tube to cause the mix- ture to settle and heat it gently (small flame). Slip a test-tube over the vertical part of the L-tube. When the gas in this test- tube, on being lighted (after removal to a distance), burns quietly, set fire to the jet issuing from the apparatus. b. Describe the structure of the flame (?). How luminous is the flame? Hold a bottle so that the flame burns inside it. If a dew appears in the bottle, what is it? Inference (?). With- draw and close the bottle, and shake the contents with some limewater (?). Inference (?). Extinguish the flame, and test the gas for acid or basic proper- ties by holding in it moistened strips of red and blue litmus paper (?). c. Summarize the observed physical and chemical properties of the gas (?). d. Place some limewater in a test-tube. When the appara- tus used in b has become cold, attach a rubber tube, add 5 c.c. of concentrated hydrochloric acid, replace the stopper, and let the issuing gas bubble through the limewater (?). Inference (?) . What, besides methane, is the other product of the reaction? Write the equations for the original action (?) and for the action of the acid on the product (?). e. Acetylene. Fill a test-tube with water. Invert it in an evaporating dish partly filled with water. Place a small piece of calcium carbide in the water, and collect the gas in the test- tube. Set fire to the gas in the test-tube. Compare the luminosity of the flame with that of methane (?). Close the tube, add a little limewater and shake (?). Inference (?). /. Summarize the observed physical and chemical proper- ties of the gas (?). Compare its density with that of air (?). g. Pour the liquid in the evaporating dish into a beaker (?). Test it with litmus papers (?). What is the suspended solid? Write the equation for the interaction of the carbide and water 82 FLAME EXERCISE 62 FLAME Object: To learn the source of the luminosity, and the structure of a flame. To find out the use of the holes at the base of a Bunsen burner. To observe the nature of the flame of a taper. Apparatus: Evaporating dish. Materials: Splints. Calcium carbonate (powdered). a. Unscrew the tube of the Bunsen burner, turn on the gas, and light it (?). Turn off the gas and replace the tube. Make a drawing of the vertical section of the burner through the feed pipe (?). Light the gas again and hold one side of the evaporating dish, first in the non-luminous flame and then in the luminous one (?). Which substance causes the light (?) and how? Why does this substance remain for a time suspended in the flame, instead of burning at once? b. Hold a splint across the luminous flame close to the bot- tom, and examine the wood (?). Inference (?). Repeat with the non-luminous flame (?). Why is the interior of the flame cold? c. Is any gas entering or escaping from the holes at the base? To answer this, light a splint, blow the flame out, and hold the smoking end close to the holes (?) . Confirm by scattering a very small amount of pulverized calcium carbonate on a piece of paper, and shaking it off so that it falls past one hole. Observe the flame (?). Hold the burner up and blow a sudden puff of air towards one of the holes (?). What is the effect of increasing the supply of air? d. Light a taper and a splint. Blow out the flame of the taper and instantly apply the flame of the splint to the ascending "smoke" (?). Repeat, noting whether the taper can be re- lighted at a distance from the wick (?). Explain. Is the flame of a taper a gas flame or not? BORAX BEAD TESTS 83 EXERCISE 63 BORAX BEAD TESTS Object : To learn the use of a borax bead for recognizing the metallic elements in an unknown compound. Apparatus : Watch-glass. Platinum wire. Materials: Borax (powdered). Cobalt chloride. Manganese di- oxide. Potassium dichromate. Ferric chloride. Nickel sul- phate. Cupric sulphate. Unknowns. a. Place some powdered borax on a watch-glass. Heat the platinum wire and dip the glowing end in the borax. Use the straight wire, without any loop. Now hold the wire in the flame and observe the behavior of the borax (?). What vapor causes it to puff up [363]? The bead must be small, to avoid its drop- ping off. Lower the flame until it is so small that it can be sheltered from drafts by the hands. Close the air-holes until a small luminous tip appears in the interior of the flame. This is the reducing portion of the flame (Why?). The blue tip and whole exterior of the flame is the oxidizing part (Why?). b. Heat the borax bead and touch with it a small particle of a compound of cobalt. Hold the glass rod between the first and second fingers of the right hand, so that when the hands surround the flame, the bead is held in the latter. Hold the bead in the oxidizing flame. Examine the bead when cold (?). If it is not distinctly colored, pick up another particle of the cobalt compound and heat again. If the bead is opaque, too much of the compound has been taken. Remove the bead and start again. To remove the bead, heat it red hot and, holding it over the sink or waste-jar, tap the wire with a pencil. Now hold the bead in the reducing flame, persistently, keep- ing the flame steady by sheltering it with the hands (?). Finally, remove the bead and make another. If this shows the cobalt color, remove it and repeat until a colorless bead is obtained. c. Repeat b, touching a particle of manganese dioxide with the heated bead, and examine in the oxidizing (?) and reducing flames (?). Tabulate the results of 6, c, d, e and / as shown on page 84 84 SODIUM BICARBONATE. ACID SALTS d. Repeat c with a compound of chromium (?). e. Repeat c with a compound of iron (?). /. Repeat with compounds of nickel (?) and copper (?). COLOR OF BEAD COMPOUND USED FORMULA OXIDIZING REDUCING FLAME FLAME g. Obtain an unknown substance and identify the metallic element in it. EXERCISE 64 SODIUM BICARBONATE. ACID SALTS Object: To prepare sodium bicarbonate by the Solvay process. To study the effect of heat on the bicarbonate and on another acid salt. Apparatus: Graduated cylinder. Test-tube (large) and cork. Trip scales. Gas generating bottle with thistle, L-, rubber, and glass delivery tubes. Test-tube, 1-hole stopper and L-tube. Test-tubes. Materials: Ammonium hydroxide (sol.). Ammonium carbonate. Sodium chloride. Marble (chips). Hydrochloric acid. Filter paper. Limewater. Sodium bisulphite. a. Preparation. Measure 24 c.c. of ammonium hydroxide solution and 12 c.c. of water into a large test-tube, add 8 g. of powdered ammonium carbonate, cork the tube and shake until the salt is dissolved. Add solid, powdered sodium chloride in excess and shake vigorously until the liquid is saturated. Decant the clear liquid into another test-tube, and lead into it carbon dioxide (made as in Ex. 59 a) until a copious precipi- tate of sodium bicarbonate has appeared. While this is going on, proceed with b. Filter, and dry the precipitate by pressing between filter papers. Note the appearance (?) and taste (?). b. Effect of Heating the Bicarbonate. Place some sodium bicarbonate in a test-tube so that the mouth is inclined slightly downwards, with the L-tube dipping into limewater. Warm the bicarbonate gently with a small flame. What gas is given off? What is deposited in the cool part of the tube? Taste the residue when cold (?). To a part, add an acid (?). What HYDROLYSIS 85 is the residue? Write the equation for the action of heat on the bicarbonate (?). c. Effect of Heating Another Acid Salt. Many acid salts [260] behave, when heated, as sodium bicarbonate did in b, and can be recognized by this behavior. Heat a little sodium bisulphite in a test-tube, clamped horizontally (?). What gas (odor ?) is given off? Is water liberated? Write the .equa- tion (?). d. Summarize the properties of sodium bicarbonate and of sodium carbonate, namely, color- (?), taste (?), effect of heat- ing (?). EXERCISE 65 HYDROLYSIS Object: To examine several salts in order to find out, by the reaction oj the solution, which interact with water and which do not, and to explain the result in each case. Apparatus : Test-tubes. Materials: Litmus papers. Sodium carbonate (sol.). Cupric sulphate (sol.). Potassium iodide (sol.). Aluminium sulphate. Lead nitrate (sol.). Sodium nitrate. a. Test some sodium carbonate solution with litmus papers (?). Explain [368] the reaction of the solution (?). b. Repeat a with cupric sulphate solution (?) and explain (?) . c. Repeat a with solutions of potassium iodide, aluminium sulphate, lead nitrate, and sodium nitrate (?). Write the equa- tion for hydrolysis in each case (?). Where there is a reaction towards litmus, explain it (?). If there is none, explain why (?). d. Dissolve a single crystal of sodium sulphide in water, and test the solution with litmus paper (?). WTiat ionic substance causes this reaction? Which of the two substances taken is capable of furnishing this ion? Formulate the interaction of the two original substances and explain it. EXERCISE 66 POTASSIUM NITRATE PREPARATION Object: To prepare potassium nitrate, and to study the influence of solubility on the products obtained in double decomposition. 86 POTASSIUM NITRATE Apparatus: Test-tubes. Trip scales. 2 beakers. Graduated cylinder. Glass rod. Watch-glass. Lens. Materials: Potassium chloride. Sodium nitrate. a. Dissolve 22 g. of potassium chloride in 45 c.c. of boiling water in a test-tube. Boil 20 c.c. of water in a beaker (set on the wire gauze) and add 25 g. of sodium nitrate. When this has dissolved, add the boiling solution of potassium chloride and continue heating for a minute or so (?). Allow the mixture to settle and immediately pour the hot liquid off the crystalline residue into another clean beaker. Examine the two products in 6 and c respectively. 6. Pour a few c.c. of hot water on to the crystalline residue, stir with a rod to wash the residue and drain away the liquid. Taste the residue (?). Dissolve a part in a very little hot water, pour several drops on a watch-glass and examine the crystals, when they appear, with a lens (?). Draw a couple of them (?). What is the substance? c. When it is cold, examine the liquid that was poured off into the beaker in a (?). What form do most of the crystals show? Are there any cubical crystals (lens)? Pour away the liquid. Dissolve the crystals in a very little boiling water and set aside. This is called recrystallization. Examine the final crystals and draw two of them (?). d. Write the equation for the action (?). Examine the fol- lowing solubilities (grams, dissolving in 100 c.c. of water at the temperatures given) : 10 100 10 100 Potassium chloride 32 57 Potassium nitrate 13 246 Sodium nitrate 80 182 Sodium chloride 36 39 The action, being a double decomposition, is reversible and therefore incomplete. All four substances were present in the mixture when the latter was first made. Which is the least soluble of the four salts at 100? Why was the sodium chloride the substance precipitated in the hot mixture? Why did potas- sium nitrate remain dissolved? Why did it come out so copi- ously when the liquid cooled? Why were there few crystals of sodium chloride mixed with it? RECOGNITION OF SUBSTANCES I 87 EXERCISE 67 RECOGNITION OF SUBSTANCES I (Mainly certain negative radicals) Object: To learn how substances may be recognized by their proper- ties, and to review the methods of preparation and properties studied in previous exercises. Apparatus: Test-tubes. Glass rod. Watch glass. Materials: Unknowns. Litmus papers. Filter paper. Sodium hydroxide (sol.). Limewater. Sulphuric acid (cone.). Barium chloride (sol.). Hydrochloric acid (cone.). a. Obtain [Instructor] a single unknown solid substance. This will contain one of the following radicals: ammonium (NH 4 ) sulphite (S0 3 ) chloride (Cl) sulphate (S0 4 ) carbonate (C0 3 ) formate (C0 2 H) sulphide (S) base (OH) In the case of a salt (except one of ammonium) we shall limit ourselves to identifying the negative radical only. The other positive radicals will, in any case, be limited to (Na), (K), and (Ca). Record at the time the result of each observation. Record negative results also. 6. External Examination [376]. Begin by recording the state (?), crystalline form (?), color (?), and odor (?). c. Solubility and Reaction of Solution. Use a few particles to find out whether it is soluble in water (?). If in doubt, proceed as in Ex. 10 /. Apply a drop of the solution to litmus papers (?). d. Effect of Heating [377]. Heat 0.5 c.c. in a dry test-tube. Watch the substance. Does it melt (?), char (?), or otherwise change (?)? Note also gases or vapors. If WATER VAPOR is given off and condenses (?), the substance may be a hydrate, an organic substance, or calcium hydroxide. Incline the tube downwards, drive all the water off, dry out the tube with filter paper, and continue heating. Does it now char (?), change (?), or give gases or vapors? 88 RECOGNITION OF SUBSTANCES II If a SUBLIMATE (solid deposit in the tube) appears (?), it is a salt of ammonium. Note the odor (?) and apply the test (Ex.51/). A COLORLESS GAS with an ODOR (?) may be ammonia, sulphur dioxide, or hydrogen sulphide, or gases from the charring of carbohydrates (see e). A COLORLESS GAS with NO ODOR. Examine for carbon dioxide by inserting a rod dipped in limewater (?). If you get a positive result, what was the unknown substance [336]? e. Effect of Sulphuric Acid [379]. To 0.5 c.c. of the sub- stance add two or three drops (not more) of concentrated sul- phuric acid (?). If necessary, warm gently (?). Watch the substance, and look out for gases. A COLORLESS GAS (bubbling), which FUMES in the breath, is hydrogen chloride. If it does fume, what was the substance [126]? A COLORLESS GAS which does NOT FUME may have an ODOR (?). If the odor is that of hydrogen sulphide, what do you infer [253]? If it is that of sulphur dioxide, inference [258, par. 4] (?). A COLORLESS GAS, which does NOT FUME and is ODORLESS, may be carbon dioxide. Test with rod dipped in limewater (?). Inference (?). It may be carbon monoxide. Try whether it is combustible (?). Inference [340] (?). If there is NO BUBBLING, there is no gas. The substance may be a sulphate. Test (Ex. 47, d) (?). It may be a base (test?). /. Report. State your conclusion, with the reasons there- for (?). g. Obtain a second unknown and proceed as before (?). EXERCISE 68 RECOGNITION OF SUBSTANCES II (Negative Radicals) Object: Same as in Ex. 67, which see. Apparatus: Test-tubes. Glass rod. Watch-glass. Materials: Unknowns. Litmus papers. Filter paper. Sodium hydroxide. Limewater. Splints. Ferrous sulphate (sol.). Sulphuric acid (cone.). Potassium dichromate (sol.). Sul- phuric acid (dil.). Ammonium molybdate (sol.). RECOGNITION OF SUBSTANCES II 89 a. Obtain [Instructor] a single unknown solid substance. This will contain one of the following radicals : peroxide (0 2 ) phosphate (P0 4 ) nitrate (N0 3 ) bicarbonate (HC0 3 ) chloride (Cl) carbonate (C0 3 ) bromide (Br) bisulphite (HS0 3 ) iodide (I) sulphite (SO,) The positive radical may be (NH 4 ), (K), (Na), or (Ca). Limit yourself to identifying the negative radical and (NH 4 ). Record immediately the result of each observation. Record negative results also. b. External Examination [376]. Record the state (?), crys- talline form (?), color (?), and odor (?). c. Solubility and Reaction of the Solution. With a few particles, try the solubility in water and, if in doubt use the method in Ex. 10 / (?). Test the solution on litmus papers (?). d. Effect of Heating [377]. Heat 0.5 c.c. Does the sub- stance melt (?), char, or otherwise change (?). Note also gases or vapors (?). If WATER VAPOR is given off (?), the substance may be a hydrate or an acid salt. To prevent cracking of the tube, re- move the water with filter paper. A SUBLIMATE indicates a salt of NH 4 (test, Ex. 51 /). A COLORLESS GAS with an ODOR (?) may be ammonia or sul- phur dioxide (Ex. 64 c). Inference? A COLORLESS GAS with NO ODOR (?). Examine for carbon dioxide (lime-water test) oxygen from a peroxide or nitrate (test), or nitrous oxide [315] (test, Ex. 54 c). Inference? e. Effect of Sulphuric Acid [379]. To 0.5 c.c. add 2 or 3 drops (not more) of concentrated sulphuric acid (?). If necessary, warm gently (?). A GAS (bubbling) with FUMES in the breath. If accompanied by a COLORED VAPOR, it may be hydrogen bromide with free bromine, or hydrogen iodide with free iodine. Nitric acid vapor, also, may be faintly colored with N0 2 [309]. Inference? A GAS which FUMES, but is NOT COLORED, may be hydrogen chloride, or nitric acid (test, Ex. 52 d). Inference? A GAS (bubbling) may NOT FUME and may NOT BE COLORED. If it has an ODOR, it may be sulphur dioxide from a sulphite or bisulphite. The latter would give sulphur dioxide under d also, the former would not. Inference? 90 CALCIUM OXIDE AND HYDROXIDE A GAS, not FUMING, NOT COLORED, and ODORLESS may be oxygen from some oxides or a peroxide (test, Ex. 40 d), or car- bon dioxide (test) from a carbonate or bicarbonate. The last would give carbon dioxide under d also, a soluble carbonate of K or Na would not, but calcium carbonate or ammonium car- bonate would do so. Inference? If there is NO GAS (no bubbling), the substance may be a phosphate (test, Ex. 55 6). Inference? /. Test the unknown for the (NH 4 ) radical (Ex. 51 /). g. Report. State your conclusion, with the reasons therefor (?). h. Obtain a second unknown and proceed as before (?). EXERCISE 69 CALCIUM OXIDE AND HYDROXIDE Object: To observe the formation of calcium oxide, and the actions of water and of an acid upon it. Apparatus : Wire gauze. 2 watch glasses. Glass rod. Evaporat- ing dish. Test-tubes. Materials: Marble (chips). Litmus paper (red). Quicklime (fresh). Hydrochloric acid (dil.) a. Select two small chips of marble. Place one on the wire gauze and heat with the full flame for 10 minutes (meanwhile proceed with c and d). Examine it and compare its appearance with that of the unheated fragment (?). Write the equation for the change (?). b. Place two strips of red litmus paper in two watch glasses. Lay one of the fragments from a on each, and moisten with water carried on a glass rod (?) What has been formed by the action of the water? Write the equation (?). What sort of oxide is calcium oxide [386]? c. Place a lump of quicklime in the evaporating dish, add a little water (only enough to wet the lower quarter of the lump) and warm gently (?). Write the equation (?). d. Place about 1 c.c. of powdered fresh quicklime in a test- tube, add dilute hydrochloric acid, shake, and warm if necessary (?). Write the equation (?). For comparison, take a chip of marble and cover it with dilute hydrochloric acid (?). Write the equation (?). What is the reason for the difference? MhA^ ir HARD WATER 91 e. Summarize the properties of marble and quicklime: color (?), appearance (?), effect of heating (?), action of water (?), action of an acid (?). EXERCISE 70 HARD WATER Object: To learn the means of detecting hardness in water, and two ways of removing temporary hardness. Apparatus: Test-tubes. Gas generating apparatus. Graduated cylinder. Materials: Soap solution (12 g. per 1.). Limewater. Magnesium chloride (sol.). a. Soft Water. To about 10 c.c. of distilled water add soap solution drop by drop, shaking between drops. Count the number of drops required before a "permanent" lather or froth is obtained (?). A "permanent" froth is defined as one which persists for three minutes. Give the name and formula of one typical component of soap [389]? b. Temporary Hardness. Take 5 c.c. of saturated limewater (1.7 g. Ca(OH) 2 per liter) and add an equal volume of distilled water. Pass carbon dioxide (made as in Ex. 59 a) through the half-saturated limewater steadily until two changes (?) have occurred (meanwhile proceed with c). Write two equations, one for each change [388] (?). The clear product is water of tem- porary hardness. What substance is present? c. Calculation of the Degree of Hardness. What weight (grams) per liter of calcium hydroxide was contained in the diluted limewater? What weight (grams) per liter of CaCOs would this give in the final product (?) d. Action of Hardness on Soap. To 2 c.c. (measured) of the product from b add soap solution (noting how much) and shake until a "permanent" lather is obtained (?). The precipitate is a calcium soap. Write the formula of a typical component of this soap (?). Write the equation and name each substance (?). e. Removing Temporary Hardness (softening). To 2 c.c. (measured) of the product from 6, add 1 c.c. (measured) of saturated limewater and shake (?). What is the precipitate [389]? Now add soap solution, noting how much is required 92 FLAME TESTS to form a "permanent" lather (?). Was the amount required as great as in d, or was it nearer the amount used in a? /. Boil 2 c.c. (measured) of the product from 6 (?). What is the precipitate? When the liquid is cold, add soap solutions as in e, to determine whether the hardness has changed (?). g. Permanent Hardness. Dissolve a crystal of magnesium chloride in 10 cc. of water, add soap solution and shake (?). Write the equation (?) and name each substance (?). h. Test the city water with soap solution (?). EXERCISE 71 FLAME TESTS (Positive Radicals) Object: To observe the characteristic colors given to the Bunsen flame by the heated vapors of compounds of six metals, and to use them for recognizing six positive radicals. Apparatus: Test-tube. Iron wire (No. 20), or platinum wire. Cobalt glass. (Optional: Spectroscope.) Materials: Chlorides of lithium, calcium, strontium, barium, sodium, and potassium. Hydrochloric acid (cone.). a. On six pieces of paper write the names of the six substances listed above and obtain on each a few particles of the proper substance. Provide 5 c.c. of concentrated hydrochloric acid in a test-tube. Hold the iron (or platinum) wire in the Bunsen flame. If the flame is colored by it, dip the wire in the acid, and hold it in the flame until the latter is as blue as usual. Clean the wire in this way (i.e., by vaporizing impurities) before and after each of the following tests. b. Heat the tip of the cleaned wire and quickly touch the first named of the substances. Hold the wire with adhering particles in the lower part of the outer blue layer of the flame and note the color of the latter (?). Repeat with the next three substances, and tabulate the re- sults, giving the name of the substance (?), its formula (?), and the color (?). c. Using sodium and potassium chlorides, view both flames through a piece of cobalt glass. Which tint of light is absorbed STARCH AND SUGARS 93 by the glass, and does not reach the eye (?), and which tint passes through and is visible? Mix the two chlorides intimately, and observe the flame with the eye (?). Which color is visible? Why is the other invisible? Now view the flame of the mixture through cobalt glass (?). Which metal can you recognize thus? d. (Optional) If a spectroscope is available, the spectra, and particularly that of sodium, should be examined. e. Obtain [Instructor] an unknown and identify it. EXERCISE 72 STAECH AND SUGARS Object: To study the properties of starch and its hydrolysis into glu- cose; and to learn the properties of two sugars, glucose and sucrose (ordinary sugar). Apparatus: Test-tubes. Flask. Funnel. Beaker. Glass rod. Graduated cylinder. Materials: Fehling's solution No. 1 and No. 2.* Starch. Hydro- chloric acid (cone.). Potassium iodide (sol.). Iodine. Sodium carbonate (sol.). Litmus papers. Sugar. Molasses. a. Starch and Glucose. Shake about 0.5 c.c. of starch with 20 c.c. of water and then boil (?). Add a few drops of the liquid to 5 c.c. of Fehling's solution and warm the latter (?). Does starch change Fehling's solution? Place three-fourths of the remaining starch suspension in a flask, set it on the wire gauze, add 5 or 6 drops of concentrated hydrochloric acid, and boil gently for ten minutes. Place the funnel in the mouth of the flask, to diminish the loss by evapora- tion, and add a little water when necessary so as to keep the volume constant. b. While this is going on, cool the rest of the starch sus- pension in running water and pour it into a beaker full of cold water. Add one drop from 5 c.c. of a solution of potassium iodide in which a single crystal of iodine has been dissolved (?). e. Cool the contents of the flask (from a) and add sodium * No. 1: 69.3 g. of CuSO 4 ,5H 2 O with water to make 1 liter. No. 2: 350 g. Rochelle salt and 100 g. sodium hydroxide with water to make 1 liter. Mix equal volumes (measured) just before use. 94 AGRICULTURE carbonate solution drop by drop, shaking between drops, and touching the edge of a piece of litmus paper with a glass rod dipped in the liquid, until the liquid gives faint alkaline reaction. Now add a few drops of this liquid to 5 c.c. (measured) of Feh- ling's solution and warm the latter [401] (?). Add more of the liquid, boil again, and continue until the blue color is gone. It takes 0.005 g. of glucose to reduce and decolorize 1 c.c. of Feh- ling's solution. What amount of glucose was contained in the part of the liquid you added? d. Sucrose. Dissolve about 0.5 g. of sucrose (ordinary sugar) in 20 c.c. of water and repeat a and c with this liquid. Does sucrose reduce Fehling's solution? Do acids hydrolyze it to give glucose? Write the equation. The hydrogen-ion of the acid acts as a contact agent. Why is it not included in the equation? e. Dissolve about 0.5 c.c. of molasses in water and test for glucose as in a, par. 1 (?). /. Tabulate the physical and chemical properties of starch, glucose, and sucrose separately as follows: color (?), solubility (?), action on Fehling's solution (?), action of dilute acids (?) EXERCISE 73 AGRICULTURE. ACID AND ALKALINE SOILS Object: To ascertain whether a soil is acid or alkaline, and to measure the acidity of an acid soil. Apparatus: Watch-glass. Wide-mouth bottle. Graduated cylin- der. Burette. Beaker. Glass rod. Materials: Soil. Potassium nitrate (sol.). Sodium hydroxide (sol.). Phenolphthalein (sol.). a. Litmus Test. Place a red and a blue piece of litmus paper on a large watch-glass. Make the soil to be tested into a paste with distilled water, and press it on to the litmus papers. Place another watch-glass, to hold the soil against the paper for 15 minutes. Note whether the soil gives an acid or an alkaline test. b. Measurement of Acidity in Soil. Place 100 g. of an acid soil in a 400 c.c. (or 12 oz.) wide-mouthed bottle. Add 250 c.c. of normal potassium nitrate, stopper the bottle, and shake the bottle at intervals of five minutes by hand. Let the mixture FERTILIZERS 95 stand overnight. Withdraw 125 c.c. of the clear liquid from the top, boil it for ten minutes to expel carbon dioxide, cool it, and titrate with normal sodium hydroxide, using phenolphthalein as indicator. Tabulate the results: (1) Titration c.c. NaOH (2) Titration c.c. NaOH Average c.c. NaOH Calculate how. much calcium carbonate would be required to neutralize the soil. EXERCISE 74 FERTILIZERS Object: To test the effect of certain fertilizers on crops. Apparatus: Large jars. Materials: Ammonium nitrate. Monocalc'um or disodium phos- phate. Potassium sulphate. Soil. Seeds. a. Essential Plant-foods. Nitrogen: Dissolve 80 g. of am- monium nitrate in 2500 c.c. of distilled water. Phosphorus: Dissolve 25 g. of monocalcium phosphate, or 26 g. of disodium phosphate in 2500 c.c. of distilled water. Potassium: Dissolve 50 g. of potassium sulphate in 2500 c.c. of distilled water. Pre- pare these solutions carefully, using chemically pure salts, and label each bottle. b. Pot-culture Test for Plant-food Requirements. Procure sufficient of a poor quality of soil to fill eight ordinary four- gallon butter jars. In the center of each pot make a drainage hole about ^ inch in diameter, cover this with a copper-wire netting, and place upon this a piece of glass wool extending over the hole. Fill each pot with the soil, pressing it in firmly. Plant the series with wheat, oats, or other suitable crop. Remove the surface layer, distribute the seed, and return the soil removed. Use sufficient seeds so that a uniform number of strong seedlings may be left in the pot (about 20 seeds). Place the pots either in a greenhouse, or in the open, but so that they will be protected from severe wind or heavy rain. Water regu- larly. To the first pot add no fertilizer. To the remaining pots add, 96 FERMENTATION at the time of planting, and weekly thereafter, 10 c.c. of the prepared solutions, as follows: Pot 2. Ammonium nitrate. Pot 3. Phosphate solution. Pot 4. Potassium sulphate. Pot 5. Ammonium nitrate and phosphate solution. Pot 6. Ammonium nitrate and potassium sulphate. Pot 7. Phosphate solution and potassium sulphate. Pot 8. All three solutions. c. When mature, the ,crop should be harvested uniformly, and weighed. Afterwards, separate the grain from the straw, and weigh the grain. Calculate the yields secured, on the acre basis. EXERCISE 75 FERMENTATION Object : To ferment some molasses and to study some of the properties of alcohol. Apparatus: Large bottle (2 1.) or flask, 1-hole stopper to fit, with L-tube, delivery tube and glass tube. Distillation apparatus (Fig. 11, Ex. 11). Wide-mouth bottle. Mortar. Materials: Molasses. Yeast. Limewater. Litmus papers. As- bestos wool. Sodium hydroxide (sol.). Iodine. a. Mix 250 c.c. of molasses with 1500 c.c. of water in a bottle or large flask. Break up a cake of yeast, shake it with water until it is completely suspended, and add it to the molasses. Plug the mouth of the bottle loosely with cotton, and set the whole in a warm place for several days. This quantity will serve for 10-15 students. For individual experiments, take one-tenth of the above amounts. 6. Fit to the bottle a 1-hole stopper, L-tube, and rubber tube, terminating in a straight glass tube. Take 15 c.c. of limewater in a test-tube, insert the glass tube to the bottom of this, and shake the fermented liquid round in the bottle (?). Note the gas evolved and its reaction with limewater (?). In what form of solution was the gas before shaking? c. Filter off 100 c.c. of the fermented liquid, place it in a flask and distil as in Fig. 11, Ex. 11 a. After 30 c.c. has come over, empty and wash the flask, and re-distil the distillate until 6-8 c.c. has come over. fM* ACETIC ACID 97 Note the odor of the distillate (?). Test it with litmus papers (?). Saturate a tuft of asbestos wool with the liquid, set the tuft on the base of the stand, and apply a light (?). Hold a cold, wide-mouth bottle over the flame, to recognize one product (?). Close the bottle and test the gas in the bottle by shaking with limewater (?). Make the equation for the combustion (?). If you burned alcohol vapor and pure oxygen, what relative volumes should you use, and what relative volumes of the products (measured as gases) would be formed? d. To a few drops of the alcohol add 1 c.c. of sodium hydrox- ide solution. Pulverize one or two (not more) crystals of iodine, add a part of the powder to the mixture and warm (?). The amount added must not be sufficient to give a permanent brown tint to the liquid. The precipitate is iodoform CHI 3 (related to chloroform CHC1 3 ). e. Summarize the observed physical and chemical properties of alcohol (?). EXERCISE 76 ACETIC ACID Object: To observe the properties of acetic acid, the difference between a strong and a weak acid, and the liberation of acetic acid from an acetate. Apparatus: Test-tubes. Materials: Acetic acid (dil. 6 N). Sulphuric acid (dil.). Zinc (dust).. Sodium acetate. Litmus papers. a. Acetic Acid. Take 5 c.c. of acetic acid and note its odor (?). Test it with litmus papers (?). To show that acetic acid is a weak acid [189], take 15 c.c. of water in each of two test-tubes. To one add the 5 c.c. of acetic acid and to the other add an equal volume (5 c.c.) of dilute sulphuric acid. Add a little zinc dust to the contents of each tube, and compare (?). Which reaction goes faster? If acetic acid had been added to the starch (Ex. 72 a) or sucrose (Ex. 72 d), instead of hydrochloric acid (a very active acid), what change in the procedure would have been necessary to get the same result? b. To about 0.5 c.c. of sodium acetate add 2 c.c. of water and 1 c,c. of concentrated sulphuric acid. Warm and note the odor 98 DESTRUCTIVE DISTILLATION (?). Test the vapor with litmus papers (?). Make the equa- tion, assuming that the second product is NaHS0 4 (?). c. Summarize the properties of acetic acid (?). EXERCISE 77 DESTRUCTIVE DISTILLATION OF WOOD AND COAL Object: To study the products obtained by distilling wood and coal, such as charcoal, coke, illuminating gas, etc. Apparatus: Test-tube (hard glass), tubing, large test-tubes and beaker. Glass rod. Materials: Sawdust and wood c'hips. Litmus papers. Bitu- minous coal (crushed). Lead nitrate (sol.). Filter paper. a. Wood. Take three-fourths of a hard glass test-tube full of sawdust and wood chips. Arrange the apparatus as in, Fig. 21. The test-tube is inclined slightly downwards towards the mouth. The wide test-tube, in which the distillate is to be caught, is surrounded by cold water, and a nozzle is inserted in one of the holes in the stopper. Heat the contents of the test-tube, at first gently, and later strongly, until no more vapors are evolved. b. During the heating, set fire to the issuing gas (?). Is the flame luminous, or not? Com- pounds of what element must be present? c. Examine the condensed liquid. What FIG. 21 liquid or liquids are seen? Test the liquid with litmus papers (?). What dissolved substance causes this reaction [420]? d. Examine, describe, and name the residue in the hard glass test-tube (?). Place it in a corked test-tube for use in Ex. 78. e. Name five observed products from distilling wood (?). /. Coal. Charge a hard glass test-tube with crushed soft coal, attach a clean test-tube to catch the distillate, and repeat a [423]. g. To test for hydrogen sulphide in the coal gas, dip a glass rod in lead nitrate solution, wipe it on a small piece of filter paper, and hold the latter in the unlighted gas (?). What compound is formed on the paper [263 and Ex. 40 c]. WOOD CHARCOAL AND BONE BLACK 99 h. Repeat b and c. j. Examine and name the residue (?). k. Name six observed products from distilling coal (?). EXERCISE 78 WOOD CHARCOAL AND BONE BLACK Object: To study the properties of wood charcoal and of bone black. Apparatus: Iron wire. Test-tubes. Crucible (porcelain). Materials: Charcoal (splinters). Splints. Litmus (sol.). Wood charcoal (powdered). Bone black. Molasses. Cupric sulphate (sol.). Ferrous sulphide. Sulphuric acid (dil.). a. Charcoal. Light first a splinter of wood and then a splinter of charcoal in the flame (?). Describe how each burns (?). What is the cause of the flame in one case (?), and of the absence of flame in the other (?) ? b. Place a splinter of charcoal in a test-tube half-filled with water. Is charcoal heavier or lighter than water? Hold the splinter of charcoal under the water by means of an iron wire, one end of which is twisted round it, and boil the water for five minutes. Remove the wire from the splinter. Does the latter now sink or float? Is carbon specifically lighter or heavier than water? Why is fresh charcoal lighter [421]? c. To a test-tube half full of water add two or three drops of litmus solution. Add about 4 c.c. of powdered charcoal, boil for five minutes, and filter. Where is the litmus? What class of substances, especially, is adsorbed by charcoal from solutions [4221? d. Bone Black [438]. Heat about 15 c.c. of bone black in the crucible (covered). The purpose of the heating is to make the charcoal more active by driving out gases and moisture already adsorbed on the surfaces of its pores. Take two test-tubes half filled with water, and add to one enough molasses to confer a distinct, tint, and to the other a few drops of cupric sulphate solution. When the bone black has cooled, put about 4 c.c. of it in each test-tube, and shake vigorously. Filter the dilute molasses. If the filtrate is still colored (?), pour it through the filter again. Taste the filtrate (?). Filter the dilute cupric sulphate, and examine the filtrate (?). 100 TESTS FOR FOOD COMPONENTS What difference do you observe? Was the sugar removed, or only the coloring matter? Explain (?). What commercial use is made of this property of bone black [402]? e. Place in a test-tube a small piece of ferrous sulphide, 10 c.c. of water and 5 c.c. of dilute sulphuric acid. Note the odor (?) and name the gas (?). When the action is well started, decant the liquid to a clean test-tube, add the rest of the heated bone charcoal (from d), shake vigorously, and note the odor (?). What property is here illustrated? EXERCISE 79 TESTS FOR FOOD COMPONENTS Object: To learn some tests for starch, glucose, milk-sugar, proteins, and fats, and to apply them to two common foods. Incidentally, to show that starch is partly digested by saliva during mastication. Apparatus : Test-tubes. Evaporating dish. Materials: Starch. Iodine (sol. in KI). Glucose (solid). Feh- ling's solution (Nos. I and II). Milk-sugar. Egg albumen. Nitric acid (cone.). Ammonium hydroxide. Woolen yarn. Fat. Cottonseed oil. Almonds (crushed). Meat. Sausage. Carbon tetrachloride. a. Starch. Place water in a test-tube, add a pinch of starch, shake, and boil (?). How does the starch change? Cool the suspension in running water, and when it is cold (not before), divide it into two parts and to one add a drop of the solution of iodine in potassium iodide (?). Keep the other half for use in e b. Take another pinch of dry starch, and add to it a few drops of the iodine solution (?). Tabulate the results of a and b, as well as those of c, d, /, and g, as follows: FOOD COMPONENT REAGENT OR TREATMENT RESULT Starch (suspension) Iodine sol. Starch (grains) Iodine sol. ? c. Glucose. Shake about 0.5 c.c. of glucose in 5 c.c. of water. Add 5 c.c. of Fehling's solution (Ex. 72, footnote) and boil (?). d. Lactose (milk-sugar): Repeat c with about 0.5 c.c. of milk-sugar (?). e. Maltose from Starch. To 5 c.c. of the starch suspension prepared in a (which itself gives no reaction with Fehling's solu- FOOD COMPONENTS OF MlLK 101 tion, Ex. 72 a), add about 1 c.c. of saliva, mix, and set aside for fifteen minutes. Then add 5 c.c. of Fehling's solution and boil (?). How was the maltose produced [430]? /. Protein. To a few particles of egg albumen, add a few drops of concentrated nitric acid (?). Add some water to wash off the acid, and pour away the liquid, leaving the solid residue. To the latter add a few drops of ammonium hydroxide (?). Repeat with a scrap of woolen yarn (?). Account for the effect of nitric acid on the skin and nails (?). g. Fat. Place on small pieces of unglazed paper (1) a par- ticle of fat, (2) a drop of cottonseed oil, and (3) part of a crushed almond; put them in the evaporating dish, and warm gently until the fat melts. Examine the papers (?). h. Examination of a Food. Rub a small piece of raw meat in the mortar with a little water until the color is removed. Then apply to portions of the meat the tests in a for starch (?) , in/ for protein (?), and in g for fat (?). j. Take a small piece of sausage and apply to portions of it the tests in a, /, and g. If the results of a and / are not definite, dissolve away the fat by shaking the fragments of sausage with carbon tetrachloride, and try a and/ again with the residue (?). EXERCISE 80 FOOD COMPONENTS OF MILK Object: To find the food components present in milk. To explain curdling. To learn a test for a common preservative, formaldehyde. Apparatus: Evaporating dish. Test-tubes. Glass rod. Materials: Milk. Nitric acid (cone.). Ammonium hydroxide. Acetic acid. Fehling's solution (Nos. I and II). Litmus papers. Iodine (sol. in KI). Formaldehyde (1% sol.). Sul- phuric acid (cone.). Ferric chloride (sol.). a. Heat 50 c.c. of milk to boiling in the evaporating dish. With a glass rod, fish out the skin which forms on the surface and transfer it to a test-tube. Apply to it the test in Ex. 79 / for protein (?). Name the substance [429]. To the milk add three or four drops of acetic acid and stir (?). How is this result to be classified? What sort of substances cause milk to curdle? What is the connection with "sour 102 FOOD COMPONENTS OF FLOUR milk"? Filter the acidified milk and test the residue on the filter for protein (?). b. To 5 c.c. of the filtrate add 5 c.c. of Fehling's solution, and boil (?). What is shown to be present (Ex. 79 d)? c. To 5 c.c. of the filtrate from a add iodine' solution (?). For what food component is this a test? Is it present? d. Put a few drops of unboiled milk on a piece of unglazed paper and heat as in Ex. 79 g (?). Result? e. Which food components have you found in milk? /. Preservative Formaldehyde. To 5 c.c. of milk in a test-tube add an equal volume of water and, by means of a glass rod, one drop (not more) of formaldehyde solution and shake. Take 5 c.c. of concentrated sulphuric acid and add to it by a glass rod one drop of ferric chloride solution. Now hold the test-tube of milk almost, but not quite vertical, and pour the sulphuric acid in a continuous stream down the side of the tube so that it may go to the bottom and form a layer under the milk. What color appears where the liquids meet? Repeat with di- luted milk free from formaldehyde (?). EXERCISE 81 FOOD COMPONENTS OF FLOUR Objects : To find the food components in wheat flour. Apparatus : Evaporating dish. Test-tubes. Beaker. Materials: Flour. Cheesecloth (squares). Thread. Iodine (sol. in KI). Fehling's solution (Nos. I and II). Nitric acid (cone.). Ammonium hydroxide. a. Take about 10 c.c. of flour, make it into a dough with water, and then place it in a small piece of cheesecloth. Bring the corners together and with a thread tie the cloth so as to enclose the dough in a bag. Knead the bag in water in the evaporating dish so long as the liquid squeezed out appears to be more milky than that in the dish. Then pour the milky liquid into a beaker to settle. Open out the cloth and wash the contents in running water until the wash-water is no longer milky. b. Test portions of the residue in the cloth for starch (?), glucose (?), and protein (?), and record the results (?). c. Test a pinch of the dry flour for fat (?). ANALYSIS OF BAKING POWDER 103 d. Pour the water away from the sediment in the beaker (from a) and test portions of the solid for starch (?), glucose (?), and protein (?), and record the results (?). e. Summarize the food components found in flour (?). EXERCISE 82 ANALYSIS OF BAKING POWDER (Qualitative) Object: Baking powders contain sodium bicarbonate, a substance which is acid (or becomes so on being heated), and starch to delay interaction. The acid (or acid-forming) substance may be potas- sium Mtartrate KHC^H^O^, or calcium acid phosphate Ca(H 2 P04) 2 , or potassium bisulphate KHSO*, or ammonium alum ( NH^ySO*, Ak(S0^3,24:H^). The object is to learn tests for the presence of the radicals of these substances. Apparatus: Test-tubes. Funnel. Evaporating dish. Platinum wire. Materials: Baking powder. Filter paper. Sulphuric acid (cone.) Nitric acid (dil.). Ammonium molybdate (sol., Ex. 55). Hy- drochloric acid (dil.). Barium chloride (sol.). Sodium hy- droxide (sol.). Litmus papers. Ammonium hydroxide (sol.). Acetic acid (dil., 6 AT). Ammonium oxalate (sol.). Iodine (sol. in KI). Cobalt chloride (sol.). a. Preparatory. Place about 4 c.c. of the baking powder into a large test-tube, add 20 c.c. of water, and shake vigorously for several minutes. Filter the liquid and test the clear filtrate as in c, d, e, and /. b. Starch (see Ex. 72 b). Perforate the filter paper and with water wash some of the residue into a test-tube. Boil this sus- pension, and then cool it and fill the test-tube up with water. With a glass rod, add to the suspension one drop of the iodine solution (?). A blue color indicates starch. c. Tartrate Radical. Place 4 c.c. of the filtrate (a) in an evaporating dish with 5 drops of concentrated sulphuric acid and evaporate to dryness over a small flame. Charring and an odor of burnt sugar indicate a tartrate. d. Phosphate Radical (see Ex. 55 b). Take 1 c.c. of the fil- trate (a) and acidify with 1 c.c. of dilute nitric acid. To 5 c.c. 104 ESTERS. SOAP of ammonium molybdate solution add 3 drops of this mixture, warm, and set in the rack (?). Phosphates give a yellow pre- cipitate. e. Sulphate Radical (see Ex. 47 d). Acidify about 5 c.c. of the filtrate (a) with 5 c.c. of dilute hydrochloric acid and add barium chloride solution (?). What is the precipitate (if any)? /. Ammonium Radical (Ex. 51 /). To 5 c.c. of the filtrate (a) add 5 c.c. of sodium hydroxide solution. Heat to boiling and note the odor (?) and reaction of the vapor (not the liquid) towards moist red litmus paper (?). What is the gas (if any)? g. Calcium Radical. Shake about 0.5 c.c. of the baking pow- der with 5 c.c. of dilute hydrochloric acid. Filter and to the filtrate add ammonium hydroxide until the liquid is alkaline to litmus. Now add acetic acid until the solution is acid to litmus, boil, and filter if the liquid is not clear. Add ammonium oxalate solution. The precipitate, if any, is calcium oxalate. h. Aluminium Radical. For test, see Exercise 95 a. j. Report. Summarize, stating which radicals were present and which absent (?) EXERCISE 83 ESTERS. SOAP Object: To learn the nature of fats (which are esters) by forming and decomposing a simple ester. To make soap and observe its properties. Apparatus: Test-tubes. Evaporating dish. Glass rod. Trip scales. Materials: Sodium acetate. Alcohol (95%). Sulphuric acid (cone.). Amyl alcohol (or fusel oil). Methyl acetate. Litmus papers. Fat or cottonseed oil. Sodium hydroxide. Hydro- chloric acid (dil.). Sodium hydroxide (sat. sol.). Sodium chloride (sol.). a. Formation of an Ester. To 1 c.c. of sodium acetate in a test-tube add 2 c.c. of alcohol and 1 c.c. of concentrated sul- phuric acid. Agitate for a minute or two, warm very slightly (do not boil!), and note the odor [349] (?). This is a test for acetic acid or an acetate. Write the equation (?), and name each substance (?). COLLOIDAL SUSPENSIONS 105 b. Repeat, using amyl alcohol instead of ordinary alcohol (?). c. Hydrolysis of an Ester. Place 10 c.c. 0% water in one test-tube and 0.5 c.c. of methyl acetate CH 3 (CO 2 CH 3 ) in an- other. Test each with blue litmus paper (?), then mix and test again [433] (?). If the result is not definite, wait a few minutes and test the mixture once more. Write the equation (?), and name each substance (?). cL Saponification of an Ester: Soap Making. Mix in a test- tube 5 c.c. of cold, saturated sodium hydroxide solution and 5 c.c. of alcohol, shake, and allow to settle (?). Pour off the upper alcoholic layer into another test-tube, add to it an equal volume of fat or cotton seed oil, and shake (?). Put the liquid into an evaporating dish on the wire gauze and set fire to the contents. Warm the dish with a very small flame to assist in driving off the alcohol. Stir until the flame goes out, and then stop heating. The pasty mass is soap, mainly sodium st ear ate and sodium palmitate [438], mixed with glycerine. Write an equation (?). Rub a little with water in the hands (?). The alcohol is used simply as a common solvent for the fat and the alkali and is employed in the laboratory experiment to save time. e. Dissolve the soap (e) in a little warm distilled water and cool. To half of the solution in a test-tube add hydrochloric acid and shake vigorously [440] (?). To show that the precipitate is an acid, withdraw it by means of a glass rod, suspend it in 10 c.c. of water in another test-tube, add a few drops of sodium hydroxide solution and heat until solution takes place. Write the equation (?). To what class of substances does / show soap to belong? /. To the other half of the cold soap solution, add sodium chloride solution (?). This is called " salting out" [439], and is a case of coagulating a colloid [442]. To what class of solu- tions does this show soap solution to belong? EXERCISE 84 COLLOIDAL SUSPENSIONS Object: To prepare a colloidal suspension, and observe its properties. Apparatus: Test-tubes. Funnel. Square bottle (20-25 c.c.). Optional: 300 c.c. beaker. 106 COLLOIDAL SUSPENSIONS Materials: Arsenic trioxide. Filter paper. Hydrogen sulphide (sol.). Sodium chloride (sol). Hydrochloric acid (cone.). Calcium chloride (sol.). Sugar. Rosin. Alcohol (95% or denatured). Optional: Ferric chloride (sol. 5%). Sodium sulphate (sol.). Sodium carbonate (sol.). a. Preparation. Shake some arsenic trioxide with 25 c.c. of cold water vigorously for several minutes, filter, and to the filtrate add an equal volume of hydrogen sulphide solution. Arsenious sulphide As 2 S 3 is formed, but remains in colloidal suspension. b. Optical Examination. Pour the suspension into a square bottle, and examine it in sunlight, or, better still, by holding it close to an incandescent bulb. Look first through it towards the light (?). Does it appear to be transparent and clear, or no? Now look at it from a position at right angles to the direc- tion of the light, and answer the same question (?). With a microscope, the particles in such solutions can be perceived, in- dividually [441]. c. Coagulation. Divide the * solution between 5 clean test- tubes. Keep one, corked, for reference. To one add sodium chloride solution (?), to another dilute hydrochloric acid (?), to the third calcium chloride solution (?), dissolve a little sugar in the fourth (?), and observe them from tune to time. Note which coagulates last (?). ^ The positive ion is here the coagulating agent. How does valence affect coagulating power? Do non-ionized, non-col- loidal substances like sugar produce coagulation? After a day or two, does the arsenious sulphide hi the refer- ence test-tube coagulate or settle of its own accord? d. Colloidal Rosin. Dissolve a single particle of rosin in 1 c.c. of alcohol. Add the solution to a test-tube full of water (?). Examine in the light as in 6 (?). Cork and keep, to see whether settling takes place (?). e. Summarize the special properties of colloidal suspen- sions (?). /. Colloidal Ferric Hydroxide (optional). Boil 300 c.c. of distilled (or soft) water in a large beaker, and add to it, a few drops at a time, 3 c.c. of ferric chloride solution. The salt is thus somewhat hydrolyzed and contains suspended ferric hydroxide Fe(OH) 3 (color ?). HOW SOAP CLEANSES 107 Examine this suspension in the light as in b (?). Take 5 test-tubes full of the prepared liquid, keep one for reference, and add to each of the others a very dilute solution of one of the following coagulants: sodium chloride, sodium sul- phate, sodium carbonate, calcium chloride. This colloid is coagulated by the negative ion. Note the time required in each case (?). What is the effect of valence? EXERCISE 85 How SOAP CLEANSES Object: To observe the power of soap solution to produce an emulsion, and to clean a test-tube brush, covered with oil and rust, separating the rust and oil from one another as well as from the brush. Apparatus: Test-tubes. Beaker (100 c.c.). Flask. Test-tube brush. Materials: Kerosene. Cottonseed oil. Ivory soap (sol. 1 :10, hot). Suspension of ferric oxide (powdered) in cottonseed oil (6 g. in 100 c.c. for whole class). a. Place 1 c.c. of kerosene in one test-tube and 1 c.c. of cotton- seed oil in another. Add about 10 c.c. of water to each, shake vigorously and place in the rack (?). Is a permanent emulsion formed? Now add to each 2 c.c. of soap solution, shake again, and observe as before (?). b. Boil 200 c.c. of water in a flask. Saturate the test-tube brush with the rust suspended in oil and push it into a test-tube. Add about 15 c.c. of the hot water, and work the brush in the tube (?). Does hot water alone remove the rust and oil? Remove the brush, pour out the water, place 15 c.c. of hot soap solution in the test-tube, and work the brush in the tube as before (?). Remove the brush, pour the contents of the test- tube into a 100 c.c. beaker, and rinse first the brush and then the test-tube with hot water, catching the rinsing-water in the beaker. Have the oil and rust been removed from the brush? After a short time, examine the contents of the beaker (?). Where is the oil (?) and in what condition? Where is the rust (?) and is it free from oil? Explain how soap solution removes grease or oil from a large object or a powder (?) 108 COMPOUNDS OF MAGNESIUM EXERCISE 86 COMPOUNDS OF MAGNESIUM Object: To study the preparation of compounds by double decompo- sition, and (in d and e) to observe the properties of the carbonate and oxide of magnesium. Apparatus : Test-tubes. Glass rod. Materials: Magnesium chloride. Sodium hydroxide (sol). So- dium carbonate (sol.). Ammonium chloride (sol.). Ammonium hydroxide (sol.). Sodium phosphate (sol.). Magnesium car- bonate (powdered). Limewater. Hydrochloric acid fdil.). a. Dissolve about 0.5 c.c. of magnesium chloride (properties ?) in 10 c.c. of water, and divide the solution into three portions. To one portion add sodium hydroxide solution (?). Remem- ber that salts, bases, and acids usually interact by double de- composition. On this basis, write the equation (?), and name each substance (?). b. To the second portion (a) add sodium carbonate solution [447] (?). Why does the addition of sodium bicarbonate to table salt containing magnesium chloride prevent the salt from becoming moist in damp weather? c. Test. To the third portion (a) add ammonium chloride solution (not included in equation), then a little ammonium hydroxide and sodium phosphate (?). Rub the inside of the test-tube with a glass rod and note where the precipitate appears (?) d. Heat 0.5 c.c. of powdered magnesium carbonate in a test- tube and lower into the gas a rod dipped in limewater (?). Write the equation (?). Use the residue after strong heating in e. e. To the residue from d, when cold, add dilute hydrochloric acid (?). What sort of oxide is magnesium oxide? EXERCISE 87 ALUMINIUM HYDROXIDE. ALUM Object: To prepare a double sail in beautiful crystals. To observe the formation of aluminium hydroxide, and its properties of coagulating suspended matter and forming lakes with dyes. Apparatus: Test-tubes (Targe). Glass rod. Trip scales. DYEING 109 Materials: Ammonium sulphate. Aluminium sulphate. Thread. Aluminium sulphate (sol.). Litmus papers. Limewater. Am- monium hydroxide. Clay. a. Ammonium Alum a Double Salt. Calculate what weight of ammonium sulphate (NH 4 )2S0 4 is required to give as many molecules as are contained in 10 g. of aluminium sulphate [469] (?). Weigh out the equivalent quantities of the two salts, and dissolve them separately, each in the smallest possible amount of hot water. Then mix the clear solutions, suspend a thread tied to a glass rod in the mixture, and set it aside to crystallize. Note the form (?), color (?), and taste (?) of the crystals. b. Aluminium Hydroxide. Dilute 2 c.c. of aluminium sul- phate solution with 20 c.c. of water. To half of the solution add about 15 c.c. of limewater (?). Write the equation. To the other half add ammonium hydroxide (?). Equa- tion (?). c. Coagulation. Take 100 c.c. of water with clay in suspen- sion, add 1 c.c. of aluminium sulphate solution, stir vigorously, and then add 15 c.c. of limewater. Observe the water after it has stood for some time (?). Explain [470] (?). d. Lakes [476]. Take some logwood solution, add to it a few drops of ammonium hydroxide, and shake. Then add 1 c.c. of aluminium sulphate solution, shake, and allow to stand (?). EXERCISE 88 DYEING Object: To try two dyes, one of which dyes cotton directly, while the other will dye it only with the help of a mordant. Apparatus: Evaporating dish. Graduated cylinder. Test-tubes. Glass plate. Materials: White cotton cloth (pieces 5x2 cm.). White flannel (5x2 cm.). Hydrochloric acid (cone.). Ammonium hydrox- ide. Chrysophenin (suspension, 1%). Sodium sulphate (sol., 8 g. Na 2 SO4,10H 2 O per liter). Alizarin (suspended, 5 g. of 20% paste to 100 c.c. water). Aluminium sulphate (sol., N). a. Preparing the Cotton. In case the sizing has not been removed from the cotton cloth, boil three pieces in 50 c.c. of 110 REACTIONS OF IRON COMPOUNDS water containing 2 c.c. of concentrated hydrochloric acid. Rinse the goods in water, dip in 50 c.c. of cold water containing 0.5 c.c. of ammonium hydroxide, and rinse again. b. Chrysophenin, a Direct Dye on Both Cotton and Wool. To 20 c.c. of water in the evaporating dish add 5 c.c. of the chrysophenin suspension (shake the bottle) and 1 c.c. of sodium sulphate solution, and heat to boiling. Place in this bath one piece each of flannel and of cotton and keep them in motion with a glass rod for two minutes. Remove them and wash in running water (?) . Is the dye fast to washing on both? What was the purpose of the sodium sulphate [476, par. 2]? Smooth out the samples on a square of glass (or a bottle) to dry, and paste them in your note-book. c. Alizarin, a Non-basic, Mordant Dye. In a test-tube dilute 2 c.c. of aluminium sulphate solution with 10 c.c. of water; place in it a piece of cotton cloth and boil for two minutes. In a second test-tube dilute 1 c.c. of ammonium hydroxide with 10 c.c. of water. Wring the piece of cloth, place it in this solution and warm and shake for two minutes. Then wring the cloth, which is now mordanted with aluminium hydroxide. In the evaporating dish put 50 c.c. of water and 5 c.c. of the alizarin suspension (shake the bottle). Place in this the piece of mordanted cloth and a piece of unmordanted cotton, and heat to boiling. Keep the pieces of cloth in motion for at least ten minutes. Finally, wash them in running water (?). Is the dye fast to washing on both? Why do they differ? % Dry the samples on glass and paste them into the note-book. EXERCISE 89 REACTIONS OF IRON COMPOUNDS Object: To try the tests for ferrous and ferric salts, and to learn how ferrous salts are changed into ferric salts by oxidation and vice versa. Apparatus: Test-tubes. 1-hole stopper. L- and delivery tubes. Funnel. Materials: Ferrous sulphate. Ferric chloride (sol.). Potassium ferrocyanide (sol.), ferricyanide (sol.), and thiocyanate (sol.). Ferrous chloride (sol.). Chlorine-water. Ammonium hydrox- ide. Ferrous sulphide. Hydrochloric acid (dil.). Iron (pow- dered). Filter paper. REACTIONS OF IRON COMPOUNDS 111 a. Tests for Ferrous and Ferric Salts. Wash some crystals of ferrous sulphate in water until the surface layer has been removed by solution. Dissolve them in 15 c.c. of water and divide into three parts. Dilute 5 c.c. of ferric chloride solution with 10 c.c. of water and divide into three parts. Test each of the salts with the three following reagents and tabulate the results: POTASSIUM POTASSIUM POTASSIUM FERKOCYANIDE FEBBICYANIDB THIOCYANATE Ferrous: Ferric: In the table, note the color produced (?), and whether there is a precipitate or simply a colored solution (?). Write the equations for the interactions with the ferric salts [497-8] (?). Potassium thiocyanate is K(CNS). Give one distinctive test for a ferrous salt (?) and two for a ferric salt (?). b. Oxidation of Ferrous Compounds. To a solution of fer- rous chloride add an oxidizing agent [219] such as chlorine-water, hydrogen peroxide (acidified), or bromine water. Then test for ferric-ion, using tests from a. What change has the ferrous-ion undergone? 4 c. Boil some water in a test-tube to remove dissolved oxygen, and cool in running water. Wash off the surface layer from a crystal of ferrous sulphate, and dissolve it in the boiled water. Now add a few drops of ammonium hydroxide (?). Shake the mixture with air, and note any changes (?). Give the name and the formula of the first precipitate (?) and of the final product (?). d. Reduction of a Ferric Compound. Dilute some ferric chloride solution. Through half of it bubble some hydrogen sulphide, made (Ex. 44 a) in a test-tube provided with a 1-hole stopper and delivery tube (?). Test small portions until the liquid no longer gives the reactions for a ferric salt. The pre- cipitate is sulphur. What change has the ferric-ion undergone? e. Boil the other half of the ferric chloride solution with iron powder for several minutes, filter, and test quickly for ferrous- ion (?). Write the equation [496]. 112 SEPARATION OF LEAD, MERCURY AND SILVER EXERCISE 90 COMPOUNDS OF LEAD. WHITE LEAD Object: To make white lead, and to learn the properties of three other compounds of lead. Apparatus: Test-tubes. 90 c.c. bottle, 2-hole stopper, L-, thistle, and delivery tubes. Materials: Acetic acid (dil. 6 N). Lead monoxide. Hydrochloric acid (dil.). Marble. Lead nitrate (sol.). Potassium chro- mate (sol.). Potassium iodide (sol.). a. In a test-tube, take 5 c.c. of acetic acid, and on a piece of paper about 3 c.c. of lead monoxide. Boil the acid, and add the lead oxide a very little at a time, noting what becomes of it (?). Finally add more water, boil, and filter to get rid of any unused lead oxide. Since the oxide interacts with acids, to what class of oxides does it belong [503]? What substance is here formed? b. Generate carbon dioxide (Ex. 59 a) and lead the gas through the filtrate (?). Give the name and formula of the precipitate [604] (?). What industry uses this process? c. Dilute 5 c.c. of lead nitrate solution and divide it into three parts. To one add dilute hydrochloric acid (?). Write the equation and name each substance (?). Indicate which is the insoluble one [505] (?). d. To the second add potassium chromate solution (?) and answer the same question as in c. e. To the third add potassium iodide solution (?) and answer the same question as in c. Boil the mixture, allow it to settle, pour off the liquid into a clean test-tube and observe it as it cools (?). Explain (?). EXERCISE 91 SEPARATION OF LEAD, MERCURY AND SILVER (Metals of Group I) Object: To learn how to use the properties of the compounds of lead, mercury (ous) , and silver for the purpose of separating these ele- ments from a mixture and identifying each when separated. Apparatus: Test-tubes. Funnel. SEPARATION OF LEAD, MERCURY AND SILVER 113 Materials: Lead nitrate (sol.). Hydrochloric acid (dil.)- Potas- sium chromate (sol.). Mercurous nitrate (sol.). Ammonium hydroxide. Silver nitrate (sol.). Filter paper. Nitric acid (cone.). Litmus papers. Hydrochloric acid (cone.). Copper foil (5 x 50 mm.). Unknowns. a. Lead Chloride. Dilute 2 c.c. of lead nitrate solution with 5 c.c. of water and add dilute hydrochloric acid, drop by drop, shaking between drops and allowing the precipitate (name it?) to settle, until the next drop produces no further precipitation. b. When the precipitate has settled, pour away the liquid (what does this contain ?). Shake the precipitate with a little distilled water, and allow it to settle, and again pour off the liquid. Now boil the precipitate with distilled water (?). c. Divide the solution into two parts. Set one aside for later observation (?). To the other add potassium chromate solu- tion (?). How should you recognize a soluble salt of lead? d. Mercurous Chloride. Repeat a and b, using 2 c.c. of mer- curous nitrate solution (?). Does the precipitate (name it ?) dissolve on boiling? Add to the suspended precipitate some ammonium hydroxide [537] (?). How should you recognize a soluble mercurous salt? e. Silver Chloride. Repeat a and 6, using 2 c.c. of silver nitrate solution (?). Does the precipitate dissolve on boiling? Divide the suspended precipitate into two parts. Set one in the strongest light available and examine it later (?). To the other part add ammonium hydroxide [521] (?). /. The Separation. Mix in one test-tube 2 c.c. each of solu- tions of lead nitrate, mercurous nitrate, and silver nitrate. Dilute with water and add dilute hydrochloric acid until the precipitation is complete. Filter, and wash the precipitate with a little cold water. To separate the lead pour 50 c.c. of boiling water through the filter, taking care to pour it over every part of the precipitate. Which compound will dissolve? Test the filtrate for the pres- ence of this compound (?). Next, to separate the silver, dilute 5 c.c. of ammonium hy- droxide with water, place a clean vessel under the funnel, and pour the solution over the precipitate (?). What do you ob- serve? Which compound is now dissolved (?) and which re- mains upon the filter? 114 DISPLACEMENT OF METALS. COUPLES A .. - ' To the filtrate, add concentrated nitric acid, until the am- monium hydroxide is neutralized (test on litmus papers) (?). Name the precipitate, and summarize the properties by which it may be recognized: Color (?), crystalline or amorphous (?), behavior towards ammonium hydroxide (?), towards light (?). Finally, to get the residue on the filter into solution for the purpose of testing it for mercury, make a little aqua regia by adding 1 c.c. of concentrated hydrochloric acid to 0.5 c.c. of nitric acid, warm the mixture, and pour it on to the residue. Catch the filtrate in a clean test-tube. Dilute the filtrate with 5 c.c. of water and put into it a small strip of clean copper foil. After a few minutes, wash the foil, rub it gently, and examine [517] (?). g. Obtain an unknown mixture [Instructor] and separate and identify the metals of this group contained in it. Re- member that negative results must be reported as well as positive ones. EXERCISE 92 DISPLACEMENT OF METALS. COUPLES Object: To study the displacement of metal-ions and hydrogen-ion by three metals. Also in f to observe the effect of a foreign metal on the displacement of hydrogen from an acid by zinc, and thereby to explain the qualities and defects of galvanized iron and tin plate. Apparatus: Test-tubes. Materials: Copper foil. Zinc, sheet. Lead, sheet. Sandpaper. Copper wire (No. 30). Labels. Lead nitrate (sol.). Mer- curous nitrate (sol.). Silver nitrate (sol). Cupric sulphate (sol.). Sulphuric acid (dil.). a. Clean the metals with sandpaper, and prepare five strips (5 X 30 mm.) of copper foil, six strips of sheet zinc and three strips of sheet lead. Attach to each, with the exception of one piece of zinc (reserved for/), a piece of copper wire 20 cm. long. b. Zinc. In five test-tubes take 5 c.c. each of solutions of the nitrates of lead, mercury and silver and of cupric sulphate and dilute sulphuric acid. Label them, noting on the label the name, formula, and positive ion in each case. Place a strip of zinc halfway into each solution and examine from time to time (?). Tabulate the results of b, c, and d as shown below. Keep the strips of zinc for use again in /. c. Lead. In three test-tubes take 5 c.c. each of solutions of MANGANESE AND CHROMIUM 115 mercurous nitrate, silver nitrate and cupric sulphate and label them as in b. Place a strip of lead halfway into each solution and examine later (?). d. Copper. Repeat b, using 5 strips of copper (?). Record negative as well as positive results. METAL SOLUTION TAKEN ELEMENT SOLUTION FORMED IN STRIP SUBSTANCE Pos. ION LIBERATED SUBSTANCE Pos. ION Zinc Lead nitrate Pb ++ Lead Zinc nitrate Zn++ Etc. e. For each positive result write an ordinary equation, and also an ionic equation [514] (?). When the result is negative, ex- plain why it is so [54] (?). /. A Couple. Place 5 c.c. of dilute sulphuric acid in each of five test-tubes. Take the sixth strip of zinc (with no wire) and the four strips of zinc which in 6 have been immersed in the salts (not the one placed in the acid), and immerse each of them as completely as possible in a portion of sulphuric acid (?). Do you observe any difference in the behavior of the clean strip and those partly coated with metal? Those coated with a foreign metal are called " couples." Which metal of the couple is attacked the more active or the less active one? Galvanized iron [419] and tin plate [508] are couples. Name the pair of metals in each (?). When each is corroded by the chemical action of water or acids, which of the two metals in each case goes into combination? In your everyday experience, which is more apt to rust, galvanized iron or tinned iron (tin plate)? Give the reason for what you have observed (?). EXERCISE 93 MANGANESE AND CHROMIUM Object: To prepare a manganate and a chr ornate. Also to study the relations of chromates, dichromates, and chromic salts. Apparatus: Platinum wire. Test-tubes. Materials: Manganese dioxide (powdered). Sodium carbonate (an- hydrous). Sodium nitrate. Chromic oxide. Potassium chro- mate (sol.). Sulphuric acid (cone.). Potassium hydroxide (sol.). Litmus papers. Potassium dichromate (sol.). Alcohol (95%). a. Sodium Manganate. On a minute scale, this substance may be made quickly in the form of a bead. Mix on a piece 116 IDENTIFICATION OF METALS IN GROUP II of paper a few particles each of manganese dioxide, sodium car- bonate, and sodium nitrate. Bend the end of the platinum wire into a long, narrow loop. Heat it and touch the mixture. Melt the mass to a bead and heat it in the oxidizing flame (?). Color (?). Write the equation [528] (?). b. Sodium Permanganate. Place the wire, with the hot bead, in a narrow test-tube containing some water and, when the bead has dissolved, examine the color of the solution by looking down through it at a piece of paper (?). Now, blow through a glass tube so that the breath (as a source of carbon dioxide) bubbles through the solution, and continue until a change is observed (?). Write the equation [629] (?). c. Sodium Chromate. Repeat a, using chromic oxide in place of manganese dioxide. Color (?). Equation (?).