GIFT OF Irs. Ynes Ivlexia v LABORATORY EXERCISES TO ACCOMPANY FIRST PRINCIPLES OF CHEMISTRY BY RAYMOND B. BROWNLEE ROBERT W. FULLER STUYVESANT HIGH SCHOOL STUYVESANT HIGH SCHOOL WILLIAM J. HANCOCK MICHAEL D. SOHON ERASMUS HALL HIGH SCHOOL MORRIS HIGH SCHOOL JESSE E. WHITSIT DE WITT CLINTON HIGH SCHOOL ALL OF NEW YORK CITY REVISED EDITION 1 ALLYN AND BACON Boston Nefo gortt Cjjicago B7 COPYRIGHT, 1908 AND 1917, BY RAYMOND B. BROWNLEE ROBERT W. FULLER, WILLIAM J. HANCOCK, MICHAEL D SOHON, AND JESSE E. WHITSIT. EDI PREFACE THIS Laboratory Manual is designed to accompany the authors' " First Principles of Chemistry." It is, in some measure, founded on Handbook 21 of the State Department of Education of New York, which was prepared by the authors in the spring of 1905, and which met with such success as to lead to the writing of the " First Principles of Chemistry." Such of the experiments from the Handbook as appear in the present Manual have been carefully revised and improved where experience has shown this to be desirable. A number of other ex- periments have been added in order to give greater freedom of selec- tion, and to provide fully for such schools as are favored with ample time for laboratory work. The authors believe that these exercises will be found to furnish a typical range of experiments suitable for an elementary course. Though practical and industrial applications receive considerable attention, yet a sound knowledge of the funda- mental facts and principles of the science is considered of most im- portance to the beginner, since it is only through painstaking labor along theoretical lines that the achievements of industrial chemistry have been obtained. It is hoped that the Manual will prove an attractive introduction to the experimental determination of chemical facts, and will lead the pupil to an interest in chemical theory for its own real and permanent value. The authors gratefully acknowledge indebtedness to that large body of chemistry teachers whose kind reception of the " First Prin- ciples of Chemistry" has encouraged them to publish the present laboratory course. NEW YORK, September, 1908. 711394 PREFACE TO REVISED EDITION THE new edition of this Laboratory Manual is the result of the authors' nine, years of experience with the first edition ; it also em- bodies the suggestions of many other chemistry teachers throughout the country. Such a thorough testing has led to the simplification of some ex- periments and to the modification of others. A special attempt has been made to have all questions on fact and theory so simple that the answers may reasonably be expected from students of average ability. Whenever additional information is needed to throw light upon the discussion, it has been freely furnished. A number of new experiments have been added in order to offer a greater range of material, so that selections can be made to fit the aims of a particular course. These additions deal with both the practical and the theoretical sides of the subject. The typography and the arrangement of the questions have been designed so as to indicate each step in the experiments. Blank spaces for answers to the questions and room for drawings make pos- sible a use of the book as manual and laboratory notebook combined. This plan is growing in favor, since it gives the student more time for experimentation and observation of laboratory phenomena. For the teacher, on the other hand, there is the advantage that the cor- recting of notebooks may be done with less drudgery and with greater efficiency. A number of new illustrations have been added .to lend interest to the work and to suggest to the students a suitable assembling of the apparatus. Half-tones have been used in preference to line drawings, so that the student will have to depend upon himself in putting into his laboratory notebook the line drawings of the apparatus. NEW JORK, June, 1917. GENERAL SUGGESTIONS TO TEACHERS Selection of Experiments. The time usually allotted to the labo- ratory work in the first course in Chemistry is not sufficient for performing all the experiments given in this manual. As an aid in the selection of a well-balanced course, the experiments are divided into the following groups : GROUP A. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 18, 19, 20, 22, 23, 24, 26, 27, 34, 36, 37, 38 or 39, 41, 42, 43, 44, 46, 47, 50, 51, 53, 61, 62, 63, 66, 67, 68, 71, 78, 79, 80. GROUP B. 12, 14, 15, 17, 21, 25, 28, 33, 48, 49, 55 or 56, 64, 65. GROUP C. 13, 29, 30, 31, 32, 35, 40, 45, 52, 54, 57, 58, 59, 60, 69, 70, 72, 73, 74, 75, 76, 77, 81, 82, 83, 84. It is recommended that all students be required to perform the ex- periments of Group A. These experiments are fundamental in their nature, and very valuable as a means of laboratory instruction. This list, together with a certain number of experiments from Group B, will satisfy the usual college entrance requirement in Chemistry. Most instructors will doubtless assign to their classes a good portion of the exercises in Group B. The several quantitative ex- periments in this subdivision are valuable for their training in manipulation, for the theory they illustrate, and for the interest they arouse. It is hoped that every laboratory section will find time for some of the experiments in Group C, particularly those dealing with the practical applications of Chemistry. The Directions for the Experiments. At first the directions for the laboratory operations are somewhat detailed. This plan has been followed in order that the beginner may have the help needed to perform the experiment readily and intelligently. As the student gains in experience and self-reliance, the directions become less full. vii Vlll GENERAL SUGGESTIONS TO TEACHERS All the questions have been put in italics so Jbhat the student will realize their importance. They should be answered in regular order for two reasons : (1) so that the student will understand what he is doing at the time the question is asked ; and (2) so that he may have information needed for later parts of the experiment. The authors have taken great care to avoid questions that the student cannot fairly or legitimately answer from the experimental data, and they have not hesitated to give fact or theory when these are necessary to a fair comprehension of the questions. Formulas for products new to the experience of the student have been given in the form of equations to be completed. When Class Discussion appears in parentheses, it means that the student requires further information in order to give a complete an- swer. Such information is often best furnished in a class discussion. When a separate notebook is used, the tabular forms for numerical data should be written in at the beginning of the experiment, so that the measurements may be recorded as soon as they are made. Some instructors find it advantageous to have the students put in the tabular forms before coming into the laboratory. Apparatus and Material. It has been the aim of the authors to use such simple forms of apparatus as are commonly found in the ordinary laboratory equipment. For their general availability, at- tention is called to the agate pans and the Syracuse form of watch glasses. This watch glass is superior to glass plates for covering and handling bottles of gas. Although the brass capsule, ramrod, and holder used in Experiments 9 and 17 can be purchased, many instructors will prefer to have them made in the laboratory shop. Accordingly, directions for making them are inserted here. The sodium capsule is made either (a) by cutting y brass tubing (-yV' wall) into pieces about an inch long, and soldering into one end a brass disk y thick ; or (6) by drilling -f^" brass rod with a -J-" or T y drill. The latter can be readily done by mounting the rod in a draw-in chuck in a lathe, first drilling and then cutting off. The handle consists of a piece of No. 14 copper or brass wire. A few turns are wrapped tightly around the capsule, and about 8" of the wire project at right angles to the capsule. The outer end of GENERAL SUGGESTIONS TO TEACHERS ix the wire should either be bent into a flat loop or be forced into a short piece of dowel rod. A ramrod of iron or brass, about 5" long, sliding easily into the capsule, should be provided. In the lists of material, concentrated acid means acid of the indi- dicated specific gravity : hydrochloric acid, 1.19, sulphuric acid, 1.84, and nitric acid, 1.42. The concentrated ammonia water should have a specific gravity of 0.90. For dilute acids and ammonium hydroxide the authors commonly employ the following concentrations : Ammonium hydroxide (1:4), that is, one part by volume of con- centrated ammonia water to four volumes of water. Hydrochloric acid (1 : 4) Nitric acid (1 : 4) Sulphuric acid (1 : 6) Early in the course, all students should be given definite directions for the safe mixing of concentrated sulphuric acid with water. The required amount of water should be measured out. Then small por- tions of the concentrated acid should be poured slowly into the water, and the mixture should be agitated after each addition. In many cases special concentrations for acids and other solutions are given at the head of the experiment. When no concentration is expressed, one to ten is understood, that is, one part by weight of the chemical to ten parts by weight of water. (A cubic centimeter of water at ordinary temperature is considered to weigh one gram.) In the majority of cases, however, one to twenty solutions will be found to work quite as well as the one to ten, with a consequent saving of reagents. It will be found convenient to have ready for the students when they come into the laboratory the solutions listed in the Material for the various experiments. Several of the experiments require solid chemicals in small amounts. In such cases, the authors have often found it advisable to distribute the chemicals on labeled slips of paper (about 5 X 10 cm.), arranged in places easily accessible to the students. In taking specified quantities of solutions, students may need graduates in some cases ; but more frequently the necessary quan- X GENERAL SUGGESTIONS TO TEACHEES tity may be measured as a fraction of a test-tubeful. The ordinary test-tube (6 x f ") contains 30 cc. In cases when only one or two cubic centimeters of a solution are to be taken, the solutions can be drawn from burettes, which should be labeled and accessible. CONTENTS PACK Care and use of apparatus . . 1 Drawings 3 Laboratory work and its record ...... 5 EXPERIMENT 1 . Setting up apparatus 7 2. Heating of metals in air 10 3. Weight change on heating a metal 12 4. Decomposition of a compound formed by heating a metal in air 14 5. Determination of the percentage of oxygen in air . . 16 6. Preparation of oxygen . . . ... . .19 7. Formation of oxides 21 8. Electrolysis of water 23 9. Decomposition of water by sodium 25 10. Preparation of hydrogen 26 1 1 . Properties of hydrogen . . . . . . .28 12. Distillation of water 30 13. Solution and suspension 33 14. Temperature and relative solubility ..... 35 15. Water of crystallization 37 16. Equivalent of magnesium 17. Equivalent of sodium . . . . 18. Preparation and properties of chlorine 19. Preparation and properties of hydrochloric acid . 20. Test for a chloride 51 2 1 . Weight of a liter of oxygen 54 xii CONTENTS EXPERIMENT PAGE 22. Bases 57 23. Alkalies 61 24. Neutralization 64 25. Titration 67 26. Types of chemical change. Direct combination. Simple decomposition ........ 70 27. Types of chemical change. Simple replacement . . 73 28. Types of chemical change. Double decomposition . . 76 29. Salts that are not neutral 79 30. Flame tests 82 3 1 . Preparation of an acid salt ...... 84 32. Preparation of sodium carbonate ..... 85 33. Determination of water of crystallization .... 86 34. Forms of sulphur 89 35. Preparation of metallic sulphides 92 36. Preparation arid properties of hydrogen sulphide . . 94 37. Sulphur dioxide, sulphite method ..... 96 38. Sulphur dioxide, reduction method 99 39. Properties of sulphuric acid 102 40. Preparation of nitrogen 106 41. Preparation and properties of ammonia . . . .109 42. Ammonium compounds Ill 43. Preparation and properties of nitric acid . . . .115 44. Preparation and properties of nitric oxide . . . .118 45. Preparation and properties of nitrous oxide . . 121 46. Preparation and properties of bromine . . . .123 47. Preparation and properties of iodine 126 48. The halogen acids 129 49. Destructive distillation 132 50. Properties of carbon 135 51. Preparation and properties of carbon dioxide . . .138 CONTENTS xiii EXPERIMENT PAQK 52. Chemical fire extinguisher . . , . . 141 53. Hard waters ... 144 54. Baking powders 148 55. Preparation and properties of carbon monoxide . . .152 56. Preparation and properties of carbon monoxide, oxalic acid method 154 57. Borax and boric acid 157 58. Water softening . 160 59. Bleaching of cotton 163 60. Four ways of preparing a salt, sodium chloride . . .166 61. Cobalt nitrate tests . 170 62. Borax bead tests '172 63. Identification of simple salts 174 64. Action of metals on salt solutions 176 65. Equivalent of silver . 179 66. Tests for iron salts . . 182 67. Action of a reducing agent on a ferric salt . . . .184 68. Action of an oxidizing agent on a ferrous salt . . .186 69. Iron salts in photography blueprints . . . .187 70. Silver salts in photography . . . ' . . .190 71. Aluminum hydroxide . . . . . . .192 72. Dyeing: substantive, salt, or direct colors . . . .194 73. Dyeing: acid colors 198 74. Dyeing: basic colors .201 75. Double salts 204 76. Qualitative separation of lead, silver, and mercury . .210 77. Chromium compounds 214 78. Fermentation 216 79. Preparation of ethereal salts 220 80. Soap making ......... 222 81. Starch 223 xiv CONTENTS KXPEEIMENT PAGE 82. Food constituents. Fats. Proteins . 226 83. Food constituents. Carbohydrates 228 84. Constituents of milk 231 APPENDIX Physical Constants of the Important Elements . . . 234 Table of Solubilities 236 General Rules for Solubility 237 Volatility of Compounds 237 Weight of a Liter of Common Gases .... 237 The Metric System 238 Pressure of Water Vapor 240 List of Supplies 241 LABORATORY EXERCISES IN CHEMISTRY LABORATORY EXERCISES IN CHEMISTRY CARE AND USE OF APPARATUS THE accompanying picture (Figure 1) gives the student the names of pieces of apparatus with which he is not familiar. These articles should be kept in a clean and orderly condition; good results cannot otherwise be secured. Figure 1 . Laboratory apparatus in common use. , test tube rack; b, bunsen burner; c, mortar and pestle; d, watch glass (Syracuse) ; e, thistle tube ; /, flask ; g, crucible ; h, reagent bottles ; j, evaporating dish ; k, funnel ; I, beakers. The Burner. The bunsen burner should burn with a clear, blue flame. The ordinary gas flame deposits soot on objects which it touches. The character -of the flame is regulated by adjusting the quantity of air that enters the holes at the base of the burner. The flame sometimes " strikes back," that is, begins to burn at the base where the air enters. This means 1 2 LABORATORY EXERCISES that too large a proportion of air is entering the tube. Give the^rubber -tubing a sudden, sharp blow with the edge of the hand. 1 If successful-, you will extinguish the flame at the base of Jthe^ b\irjier : 'and; produce a colorless flame at the top of the 'burner. " If not; successful, turn off the gas, adjust the movable ring, and relight the burner. Heating Glassware. Test tubes may be put directly in the flame ; beakers and flasks should be protected by wire gauze or asbestos mat. When glass apparatus contains a liquid, the flame should never extend above the liquid in the vessel. Never attempt to heat articles made of thick glass, such as bottles and battery jars, because the poor conductivity of glass causes un- equal expansion and breakage. Heating Porcelain. Evaporating dishes and crucibles can be heated to very high temperatures. Crucibles can be put di- rectly in the flame, but evaporating dishes should be placed on wire gauze with asbestos center. In both cases the heat should be applied slowly at first. Setting up Apparatus. (#) Have everything firmly arranged and securely placed. (5) Place the weight of the object directly over the base of the ring-stand. (- phosphorus oxide Allow the action to continue overnight. (5) The next day, remove the tube from over the phos- phorus, but still keep the mouth of the tube beneath the water. Then raise or lower the tube until the water is at he same level inside and outside. Read and record in the table the volume of the gas remaining in the tube. Record the temperature of the water and the barometric pressure. Applying Charles' law and Boyle % law, find the volume which the gas that remains would occupy if it ivere at standard conditions. The difference between the original volume of air inclosed and the volume of gas that remains, both corrected to standard conditions, represents the amount of oxygen removed by the phosphorus. Calculate the - percentage of oxygen in the air. Make all calculations in your note book. TABLE Volume of air taken cc. Temperature of air taken C. Pressure of air barometer reading mm. Corrected volume of air cc. Volume of gas remaining in measuring tube cc. Temperature of gas remaining C. Pressure of gas remaining (barometer reading) mm. Corrected volume of gas remaining cc. Volume of oxygen removed by phosphorus cc. Percentage by volume of oxygen in air % LABORATORY EXERCISES CALCULATIONS PREPARATION OF OXYGEN 19 EXPERIMENT 6 Preparation 01 Oxygen by the Decomposition of a Chlorate APPARATUS. Two test tubes ; delivery tube ; rubber stopper ; ring- stand with clamp ; bunsen burner ; four 6-oz. wide-mouth bottles ; four glass plates for wide-mouth bottles ; enameled pan, or pneumatic trough ; watch glass ; funnel. MATERIAL. Potassium or sodium chlorate ; manganese dioxide ; filter paper ; splinter. In this experiment there is danger of the water " sucking back " into the hot test tube. Guard against this by removing the delivery tube from the water before the flow of gas stops. (a) Mix thoroughly about 8 grams of potassium chlorate and 6 grams of manganese dioxide. Place in a test tube pro- vided with a delivery tube. Clamp the test tube in a position - Figure 9. convenient for heating (Figure 9). If a pneumatic trough is used, adjust the delivery tube to deliver the gas just below the opening in the bridge of the trough. Carefully regulate the heating so as to cause a very gentle evolution of the gas. Do not heat the test tube sufficiently to make the flame yellow. 20 LABOEATOEY EXERCISES (5) Collect a test-tubeful of the gas and test it with a glow- ing splinter. Eesult ? Collect the remainder of the gas in wide-mouth bottles. Cover with glass tubes and keep for Experiment 7. (c) Remove the delivery tube and allow the test tube to cool. Nearly fill the test tube with hot water, close the mouth of the tube with the thumb, and shake the tube. Pour the muddy liquid on a moistened filter paper fitted to a funnel. Collect the clear liquid (filtrate) in a test tube. Remove a small portion of the black residue from the filter, place it on a second watch glass, and set it aside to dry. Which of the original substances does the black residue resemble f Taste a crystal of potassium chlorate. Then taste the clear filtrate. Do they taste alike ? fa i Is the substance in the filtrate potassium chlorate or a different substance $ From which of the original substances was the oxygen probably derived f / J n Ci-<4 ( : wo- Complete the equation : potassium chlorate >- potassium chloride + [ potassium \ chlorine 1 oxygen chlonne potassium The manganese dioxide causes the oxygen to be liberated more regularly and at a lower temperature. FORMATION OF OXIDES 21 t^+t*- ^#6*4. -^ s**t<<9, , EXPERIMENT 7 Formation of Oxides / APPARATUS. Deflagrating spoon ; asbestos paper ; bunsen burner. MATERIAL. Four bottles of oxygen ; splinter of charcoal ; magnesium ribbon, 5 cm. long ; sulphur ; red phosphorus. () Place a thin splinter of charcoal across the bowl of a clean deflagrating spoon. Heat the end of the splinter until it glows brightly, and immediately lower it into a bottle of oxygen* Does the charcoal burn with aflame ? Compare the intensity of the action in oxygen with that in air. Of what elements does the gas formed probably consist ? (6) Twine a piece of magnesium ribbon around the rod of the deflagrating spoon, allowing the upper end to project slightl} r . Light the free end and lower the spoon into a bottle of oxygen. Compare the combustion of the magnesium with that of the carbon. ' Compare the action in oxygen with that in air. What is the appearance of the oxide of magnesium ? Does this seem to be the same material as that obtained when magnesium was burned in air (Experiment 2) ? (c) Clean the spoon, line it with asbestos paper (baking sheet), and put on the paper a small piece of sulphur. Heat the sulphur by directing the flame of the burner against it until it lights, and then lower it into the bottle of oxygen. Describe the burning of the sulphur in oxygen. *-- magnesium -f- oxygen >- / /, , sulphur 4- oxygen >- phosphorus + oxygen >- ELECTROLYSIS OF WATER 23 EXPERIMENT 8 Electrolysis of Water APPARATUS. Electrolysis apparatus like that shown in Figure 10; battery jar, 4 x 5" ; 3 dry cells and connections, or 100-watt lamp and socket with connections for 110 volt direct current; bunsen burner ; two test tubes. MATERIAL. Sulphuric acid, 1 to 20 ; splinter. (0) In a small battery jar, place water containing 1 part of sulphuric acid to 20 of water. The use of the acid is to make pos- sible the passage of the current through the water. Set the electrolysis block firmly on one side of the jar (Figure 10). Fill two test tubes with a mixture of acid and water, cover the end of each tube in turn with your forefinger, and invert it into the water of the battery jar. Remove the finger after the mouth of the test tube is below the surface of the water. Slip each tube into the clamp on one side of the small board and carefully push it down over the electrode until the latter is entirely within the tube. Thoroughly rinse the hands to remove all traces of acid. (6) Connect the two binding posts with a battery of three dry cells in series, or with a 110-volt direct current circuit, having a 100-watt incandescent lamp in series between the source of current and the electrolysis apparatus (Figure 11). Determine the di- rection of the current as directed by the instructor. The electrode through which the current enters is the anode ( + ) The current leaves the solution at the cathode ( ). Figure I 1 I p. f~Y In I y Figure 11. 24 LABORATORY EXERCISES As soon as the water in one of the tubes has been displaced by gas, remove the tube from the battery jar, keeping it mouth downward. Hold the mouth of the tube to a flame. Result? d M, . .' - When the other tube has filled with gas, close it with the thumb and remove it from the battery jar, inverting it at the same time. Insert a glowing splinter into the gas. Result ? What gas collects at the anode ? Is the same gas liberated at the cathode ? (- DECOMPOSITION OF WATER BY SODIUM 25 EXPERIMENT 9 Decomposition of Water by Sodium APPARATUS. Brass capsule, provided with a holder ; brass ramrod to fit capsule ; pan ; test tube or bottle ; bunsen burner. MATERIAL. Sodium. Caution ! The action of sodium with water is very violent. Avoid danger by fol- lowing directions. Nearly fill a metallic capsule with freshly cut sodium from which all the crust has been removed. The sodium must be pressed firmly into the capsule. Place the capsule in a wire holder, and, holding the cap- sule mouth downward, thrust it under the mouth of an in- verted test tube or small wide- mouth bottle filled with water. Control the evolution of the Fi s ure 12 - gas by slightly inclining the capsule (Figure 12). If careless handling allows the sodium to escape from the capsule, stand aside. When the test tube is filled with gas, carry it mouth down- ward to a flame. Remit f 4 v / / of -- Q-'/.. i ;v * ' Under no circumstances add more acid, nor in any way interfere with the generator without consulting the instructor. PREPARATION OF HYDROGEN 27 (5) Collect the gas in a test tube. As soon as the test tube is filled, hold it mouth downward to a small flame. Continue to collect and test the gas in this manner until a portion burns quietly. The hydrogen is now ready to be collected for Ex- periment 11. Fill three bottles with the gas. Leave them standing on the shelf of the pneumatic trough, or cover them with glass plates and set them mouth downward on the desk. H^ Proceed to Experiment 11, part (a). (c) Filter a few drops of the liquid in the generating bottle into a watch glass. Place this on the top of a beaker one third full of water, and boil the water until a solid has appeared in the watch glass. Examine this solid and describe its appearance. The compound is zinc sulphate, which is composed of zinc, sulphur, and oxygen. Complete the equation : zinc + sulphuric acid >- -\- f hydrogen | sulphur [oxygen I ^ ^ From what material does the hydrogen come ? Why is the action called a replacement action ? /. Why icas the gas collected in test tubes only and repeatedly tested in the first part of the experiment ? 28 / .^:;& -f //, .' LABORATORY EXERCISES EXPERIMENT 11 Properties of Hydrogen APPARATUS. Glass tube (20 cm.) ; test tube ; clamp ; bunsen burner. MATERIAL. Copper oxide (wire form) ; taper. (a) Replace the end of the delivery tube of the generator used in Experiment 10 with a straight, dry glass tube, and let it lead to the bottom of a nearly horizontal test tube that contains a little copper oxide (wire form) (Figure 14). Allow the hydrogen to pass into the tube for two minutes to expel the air. Then heat the tube directly under the copper oxide. When the hydrogen passes over the heated copper oxide, what collects in the cool portion of the tube? What is left in the heated portion ? Figure 14. Hoy) do you account for the production of these substances ? ,ff .< & W/yU vj ' element was removed from the copper oxide by the hydrogen ? A material which acts in this way is called a reducing agent. Complete the equation : copper oxide + hydrogen >- . /^ + f copper [ oxygen (6) Holding a bottle of hydrogen mouth downward, thrust into it a lighted taper. What happens to the flame of the taper ? PROPERTIES OF HYDROGEN What is occurring at the mouth of the bottle 9 29 Slowly withdraw the taper from the bottle. Explain the result. / / J " $ / '&fr/UAr x4-^^< ' '*4,4of~it ^^ / " 1 ^ Name the soluble substance. (5) Distribution of the solute in the solvent. Put half a teaspoonful of table salt in a beaker of water and stir the mixture. Is the solution clear and transparent ? v'" > Dissolve a teaspoonful of powdered sodium chromate in a beaker of water by stirring thoroughly. Is the solution clear f Is it transparent f What does the uniformity of color indicate concerning the dis- tribution of the dissolved substance (the solute) in the water (the .'&^& ** A * > > ^ ' v j( y'^- fJ *' // ^ *-a - (>) Heat a few crystals of sodium sulphate carefully in a dry test tube, holding the tube in a horizontal position. What collects on the walls of the test tube f yasfcu- To what is the change in weight noticed in part (a) probably due? , (' ^^j-^CL^.^^^-1^ What happened when the residue ivas dissolved and allowed to cool? $J, / (d) In separate dry test tubes gently warm a few crystals of potassium chlorate, zinc sulphate, 1 barium chloride,^ potassium sulphate^ potassium nitrate, and alum. Record the results in the following tabular form: TABLE SUBSTANCE HEATED Is WATER DEPOSITED IN COOL PORTION OF TURK ? APPEARANCE OF RESIDUE &>*, -ei Do all crystalline substances contain water of crystallization? Illustrate. EQUIVALENT OF MAGNESIUM 39 EXPERIMENT 16 Equivalent of Magnesium APPARATUS. Gas-measuring tube, 50 cc. ; battery jar ; thermometer ; barometer. MATERIAL. Magnesium ; concentrated hydrochloric acid ; thread ; water for the battery jar that has stood long enough to come to the room temperature. The data for this experiment should be tabulated as shown on page 41. Pour about 5 cc. of concentrated hydrochloric acid into a gas- measuring tube. Fill the remainder ot the tube with water, taking care not to mix the acid and water ; the heavier acid will remain at the bottom. Roll a piece of magnesium whose exact weight is known (about .045 gram), 1 into a loose coil somewhat smaller than the inside diameter of the tube. Pass a thread through the loop of the coil, and tie it. Put the magnesium into the measuring tube, holding the thread so that the magnesium will not sink. Close the hibe with the thumb, and invert it into a battery jar of water, rest- ing the mouth of the tube against the bottom, so that the thread will be held. Allow the magnesium to rise not quite to the graduation in the tube (Figure 16). The heavier acid will flow down and react with the magnesium. What is the gas that collects ? &*; Figure 16. From what substance does it came f 1 Weigh a strip of magnesium ribbon several meters in length. By calcula- tion, determine the length of a piece that will weigh the required amount. Cut off pieces of this length. 40 LABORATORY EXERCISES Complete the equation : magnesium -{- hydrochloric acid >- - | hydrogen L chlorine + r Why is this reaction termed a replacement ? When the action has ceased (all the metal being dissolved), adjust the levels. Read the volume of hydrogen obtained and record your result. Record the temperature of the liquid in the jar and the barometric pressure. Correct the pressure for aqueous tension. ( Use the table on page 240.) Make all calculations on page J^l. Reduce the volume of hydrogen to standard conditions. The weight of 1000 cc. (1 liter) of hydrogen is 0.09 g. Calcu- late the weight at standard conditions of the hydrogen that was produced by the reaction, using the proportion : corrected volume A nn 1000 cc.: , , , :: 0.09 g. : x g. of hydrogen This result is the weight of hydrogen that is liberated by the action of your known weight of magnesium. Calculate how much magnesium would have been necessary to liber- ate 1 gram of hydrogen. This weight is called the equivalent of magnesium. The equivalent of any element is the weight of that element that replaces (or combines with) i gram of hydrogen. EQUIVALENT OF MAGNESIUM 41 TABLE Weight of magnesium taken W*/g Volume of hydrogen obtained . . . 3f.$> cc. Temperature - - If.u c. Barometric pressure . . 7^ J mm. Aqueous tension . . . . ' . V. . . - q mm. Corrected pressure Volume of hydrogen under standard conditions . / J ' 7 ;:;:wr Weight of hydrogen (calculated) ... g. Equivalent of magnesium (calculated) .... . . . /,., CALCULATIONS 42 LABORATORY EXERCISES EXPERIMENT 17 Equivalent of Sodium APPARATUS. Metallic capsule and holder ; brass ramrod to fit capsule ; horn pan balance ; weights ; 16 oz. bottle ; graduate, 500 cc. ; pneu- matic trough ; glass plate ; barometer ; thermometer. MATERIAL. Sodium. Caution ! Remember that the action of sodium with water is very violent. TJie data for this experiment should be tabulated as indicated on page 43. (a) Weigh a metallic capsule that is clean and dry. Record its weight in the table. Nearly fill the capsule, as in Experiment 9, with freshly cut sodium freed from any adhering crust. Wipe off any oil with filter paper. Weigh the capsule and contents quickly. Record the weight. (5) Fill the wide-mouth bottle with water and measure its capacity by pouring the water into a graduate. Record the volume. (c) Then fill the bottle with water and invert it in the trough. Place the metallic capsule in its holder. Raise the bottle in the trough with the left hand. Take the holder in the right hand and incline it so that the open end, of the cap- sule will be downward. Keeping the open end downward, thrust the capsule under the mouth of the bottle. Control the evolu- tion of the hydrogen by slightly inclining the capsule. (c?) When the action ceases, adjust the bottle so that the liquid on the inside is level with that outside. Close the mouth of the bottle with a glass plate, remove it from the trough, and set it on the desk, mouth upward. Pour the liquid now in the bottle into a graduate. Record its volume. EQUIVALENT OF SODIUM 43 Record the temperature of the liquid in the trough and the baromet- ric pressure. Correct the pressure for aqueous tension. {Use table on page 240.) Reduce the volume of hydrogen to standard conditions. The weight of one liter (1000 cc.) of hydrogen at standard conditions is 0.09 gram. Calculate the iveight of hydrogen evolved. Then determine ivhat weight of sodium is required to liberate 1 gram of hydrogen. This weight is called the equivalent of sodium. The equivalent of any element is the weight of that element that replaces (or com- bines with) i gram of hydrogen. Make all calculations on page 44. TABLE g. Weight of capsule Weight of sodium taken Capacity of bottle g. cc. Volume of liouid left in the bottle .... . cc. Volume of hydrogen obtained . Temperature of hydrogen . ... cc. C. Barometric pressure mm. Aqueous tension mm. Corrected pressure mm. Volume of hydrogen at standard conditions cc. \Veight of the hydrogen (calculated) Equivalent of sodium (calculated) 44 LABORATORY EXERCISES CALCULATIONS PREPARATION AND PROPERTIES OF CHLORINE 45 EXPERIMENT 18 Preparation and Properties of Chlorine APPARATUS. Flask ; two-hole rubber stopper ; thistle tube ; four wide- mouth bottles (6 oz.), with two-hole rubber stoppers; eight glass bends ; four rubber connectors ; ring- stand with large ring ; pan of water ; bunsen burner ; four glass plates or watch glasses (Syracuse form) ; one hydrogen generator, provided with jet tube, for the class. MATERIAL. Concentrated hydrochloric acid ; manganese dioxide ; taper ; colored cloth ; powdered antimony^ Caution! Chlorine is a poisonous gas. Do not inhale it. Inhaling ammonia or alcohol will counteract some of its effects. (a) Preparation. Arrange apparatus as in Figure 17. Pour a small amount of water into the fourth bottle. If good hoods are available, Figure 17. Figure 18. use the apparatus shown in Figure 18. In this case, the solubility should be determined by passing the gas into a test tube of water. Place in the flask 15 cc. of concentrated hydrochloric acid and 46 LABORATORY EXERCISES add about 8 grams of granular manganese dioxide. Rotate the flask so as to mix its contents, then replace the stopper. Heat the water in the dish under the flask to boiling. Describe the action in the generator. (>) Physical properties. Hold a piece of white paper behind the first bottle. What is the color of chlorine ? How can you tell when the bottle is filled with (/as ? / '.' /" '" ' / , ' ; \ When the bottles are filled with chlorine, withdraw the flame. Keep the gas for use in parts (c), (d), and (e}. Is chlorine soluble in water ? Give a reason for your answer. < (c) Chemical properties. The instructor at this point should introduce a jet of burning hydrogen into a bottle of chlorine. What compound is formed when hydrogen burns in oxygen ? Wliat is formed ivhen hydrogen burns in chlorine ? cS':<.i^#le* The instructor should also sprinkle a pinch of powdered anti- mony into a bottle of chlorine. Result ? Is oxygen necessary for combustion ? : i Lower a lighted taper into a bottle of chlorine. The taper is composed of compounds containing hydrogen and carbon. Which of these elements is liberated when the candle burns in chlorine f ^^% ^^ /" PREPARATION AND PROPERTIES OF CHLORINE 47 (d) Bleaching action of chlorine. Place a piece of dry colored cloth in one bottle of chlorine unil a piece of wet cloth in another. Cover the mouths of the bottles with glass plates. What must be the condition of the cloth to be bleached by chlorine ? Explain the bleaching of cloth by chlorine. (Class discussion.) (e) General questions. Hydrochloric acid is a compound of hydrogen and chlorine. With what does the oxygen of the manganese dioxide combine f ^ptertz^ - Wliat is your conclusion as to the chemical activity of chlorine as compared with oxygen. With u'hat elements does <-ltlorinp readily combine ? /*4*r2^ ^Z/T DRAWING ' / / , 48 LABORATORY EXERCISES EXPERIMENT 19 - Preparation and Properties of Hydrochloric Acid APPARATUS. Flask, 250 cc., with stopper carrying thistle tube and delivery tube ; ring-stand with one ring and one clamp ; wire gauze with asbestos center ; bunsen burner ; two test tubes ; wide-mouth bottle ; enameled pan. MATERIAL. Sodium chloride ; sulphuric acid, 2 to 1 ; blue litmus paper ; magnesium ; zinc. (#) Preparation. Pour about 20 cc. of sulphuric acid (2 to 1) into a flask sup- ported on a wire gauze on a ring-stand, and add about 10 grams of sodium chloride. Gently rotate the flask so as to mix the acid with the chloride. Close the flask with a stopper carrying a thistle tube and a delivery tube arranged for the collection of gas in a dry test tube by downward displacement. If neces- sary, heat the flask with a small flame. Describe the action in the generator. Of ivhat elements is hydrogen chloride composed f : v >$/>>.?<>.. $' "J : - ' l^'' L Which of the original materials furnished the chlorine f / ff > / Which furnished the hydrogen? : In this particular case, sulphuric acid is used because it does not vaporize below 338, so that none of it passes off with the hydrogen chloride. sodium sulphuric sodium hydrogen chloride acid ' sulphate chloride c^l sodium i ,( chlorine hydrogen \j u sulphur oxygen sodium f/ 7 ^.- -^ J > ''"' ;/ sulphur oxygen Why is'hydrogen chloride collected by the method used f PROPERTIES OF HYDROCHLORIC ACID 49 (5) Solubility of hydrogen chloride. Fill a dish with water and set it on the table. Take the test tube of gas collected by the downward displacement of air, close its mouth tightly with the thumb, invert the test tube, and hold its mouth below the surface of the water. Remove the thumb. *&* *rf n svw AS***-, *ju ff&f-f Explain why the gfos is not collected over water. Result? i Close the mouth of the test tube with the thumb and remove it from the water. Moisten a piece of litmus paper with the liquid contained in the test tube. Result? Taste the liquid. Result? These effects are typical of the water solu- tion of acids. The solution in the reagent bottle marked " hydrochloric acid " is also prepared by dissolving hydrogen chloride in water. (c) Density of hydrochloric acid. Pour not more than 10 cc. of water into a wide-mouth bottle. Place the mouth of the delivery tube within half a centimeter of, but not touching, the surface of the water in the bottle (Figure 19). Heat the flask with a small flame, or by a pan of boiling water, for at least ten minutes. While doing this, occasionally look through the water in the bottle horizontally. Is the solution of hydrogen chloride formed heavier or lighter than Figure 19. water? Explain Jr* 50 LABORATORY EXERCISES Action of hydrochloric acid with metals. Pour half of the solution just made into a test tube and drop into it a strip of magnesium. Bring a flame near the mouth of the tube. Results? Place a piece of zinc in another test tube and pour the remain- ing hydrochloric acid upon it. Test the gas with a flame. Results'! What substance is liberated ivhen hydrochloric acid reacts with these metals ? . /- / , ^.Magnesium and zinc are elements. / When hydrochloric acid reacts with these metals* where does the substance that is liberated come from ? /%#']' 'g^fa**' What becomes of the metal? "' What three properties have been mentioned as characteristic of acids? ^/t n^ #.ity - AwUdt 'DRAWING TEST FOR A CHLORIDE 51 - Any solid which thus separates out of a clear liquid is known as a precipitate. Describe the silver chloride precipitate as to color and appearance. Set aside the tube containing the precipitate. (li) Take a little of a solution of sodium phosphate and add to it silver nitrate solution. Result f Complete the equation : ^L4 rt^w? : '2 / L^ What gas is liberated f Determine the action of the solution 011 litmus and rub some of it between the fingers. Results f Evaporate part of the solution to dryness. The substance left in the dish is sodium hydroxide. Describe its appearance. Complete the equation : Na+ HOJf ^ NaOH Is sodium hydroxide a soluble base ? 5H LABORATORY EXERCISES (5) Some bases can be prepared by action of the oxide of the metal with water. Place a gram of quicklime (calcium oxide, CaO) in a test tube and add 1 cc. of water. Warm the mixture until the action starts ; remove the tube from the flame and see if there is continued action between the quicklime and the water. If not, warm the tube until an action begins and continues without the further addition of heat. Describe the action. , Mi* How does the substance formed compare ivith the original lime ? /u r ' This new substance is slaked lime (calcium hydroxide, Oa(OH) 2 ). Write an equation for its formation. Ca. Add water to the slaked lime, shake thoroughly, and allow the solid'- to settle. Pour off the clear liquid into another test tube, retaining the solid for part (d). Determine the action of this solution on litmus. Result? A Is calcium hydroxide a soluble base ? State reasons for your '/ answer. Ct^itf. ' '- K.U- uwi^tt v / A-/,-/L. m & **' f^ 7 / What common property have the solutions of sodium hydroxide and calcium hydroxide ? // f /,-f^'V.A^ /y .' / . This is one of the characteristic properties of the solutions of metallic hydroxides (basee^. BASES 59 (c) Other bases can be prepared by a process of precipitation. To 5 cc. of a hot solution of ferric chloride add 4 cc. of am- monium hydroxide. , V *^AP^jJjArtAL ^V-i**^ *- Result ? <<. ; ^v^ / Complete the equation : FeCl 3 + 3 NH 4 OH-^Fe(OH) 3 Filter the solution and thus obtain the ferric hydroxide on a filter paper. Wash it thoroughly, using three separate portions of water. Allow each portion of the water to drain through completely before the next is added. Transfer the washed precipitate to a test tube, add 5 cc. of water, and shake the mixture thoroughly. Allow the precipi- tate to settle and pour off most of the clear liquid. This is to complete the washing of the ferric hydroxide. Add 5 cc. of water, shake the mixture, and determine its action on litmus. Is there any evidence that ferric hydroxide is soluble ? Retain the contents of the tube for part (6?). What characteristic must bases have in order to act on litmus ? .^vwWxVfe *^WU*_. - <* Determination of the action of bases with acids. Place in one test tube sodium hydroxide solution, in a sec- ond, some of the solid calcium hydroxide from part (>), and in a third, the ferric hydroxide from part (c). To each add 5 cc. of hydrochloric acid. Determine whether heat is produced in each case. Results*^ Do you observe any other erirlvnces of chemical action ? ^t 60 LABORATORY EXERCISES Complete the equations : NaOH + HC1 Ca(OH),+ HC1 Fe(OH) 3 + HC1 TABLE NAME OF BASE SOLUBLE OB INSOLUBLE ACTION ON LITMUS ALKALIES 61 /<* 14 EXPERIMENT 23 Alkalies APPARATUS. Six test tubes; two beakers, 150 cc. ; evaporating dish; ring-stand with ring ; wire gauze with asbestos center ; bunsen burner ; glass rod. MATERIAL. Washing soda ; borax ; sodium sulphate ; baking soda ; solution of sodium hydroxide, 10 g. to 100 cc.; solution of ammo- nium hydroxide, 1 to 3 ; pieces of cloth with small grease spots of butter ; cotton cloth ; woolen cloth ; red litmus paper. The term alkali is applied to any substance whose water solu- tion turns litmus blue. The soluble bases are strong alkalies, but solutions of many other substances also produce the same change in the color of litmus. (a) Alkaline reactions. Dissolve a little of each of the following substances in water, and test the action of its solution on litmus : washing soda, Na 2 CO 3 ; borax, Na 2 B 4 O 7 ; sodium sulphate, Na 2 SO 4 ; baking soda, NaHCOg. Results in each case f S J/a Q 3 ^^ +u * . /Vft 2 6} AA+? +- NaOH + / {'la (7>) Alkalies as solvents for grease. Put into a beaker a piece of cotton cloth, on which a very small grease spot has been made with a little butter. Add sodium hydroxide solution, and boil the contents for several minutes. Remove the cloth and examine it to see if the grease spot has been affected. Result f Using a solution of borax as the alkali, repeat the experiment . Result f Which of the two filJfalles Jias the greater grease-dissolving power 9 (- HO + 66 LABORATORY EXERCISES () Dissolve about half a gram of potassium hydroxide in a test tube full of water, and, proceeding as in (a), neutralize the solution with dilute nitric acid, Evaporate the neutral solution to dryness. The residue is potassium nitrate, KNO 3 . Write the equation for the neutralization. ' ; / ' k "A . I-/ \l v>- '-A'-'-- ' !/'/^ -4 t-i ' - i Potassium nitrate is called a salt, that is, it is a compound formed by the combination of a metal with an acid radical (an acid minus its replaceable hydrogen). What radical (group of elements that tend to ding together during a chemical change) is present in every base ? What element is contained in every acid ? What becomes of the characteristic radical of a base and the characteristic element of an acid during neutralization ? 2^- What becomes of the remainder of the base and the remainder of the acid ? 1 Complete the general statement concerning neutralization : acid + base *- + Complete the following equation used to represent the dissociation of sodium hydroxide dissolved in ivater: NaOH -*- Na+ + Which ,of these ions is present in a water solution of any base ? Write the_ equation^representing the dissociation of hydrochloric acid. Q, t ^ h What ion is present in a water solution of any acid f What compound results from the combination of the ion character- istic of acids with the ion characteristic of bases f Write the reversible equation for the reaction between the metallic ion of the base and the negative ion of the acid. CONCENTRATION OF A SOLUTION BY TIT RATION C7 EXPERIMENT 25 ^ Determination of the Concentration of a Solution by Titration APPARATUS. Two burettes ; beaker or Erlenmeyer flask ; stirring rod ; ring-stand with two clamps. MATERIAL. Solutions of hydrochloric acid (preferably fifth-normal, made by dissolving 17 cc. of concentrated hydrochloric acid in 500 cc. of water, and then making up the volume to 1000 cc.), sodium hydrox- ide, and phenolphthalein (made by dissolving 1 gram of phenolphthalein in 100 cc. of 50 % alcohol). A normal solution of an acid contains 1 gram of replaceable hydrogen per liter. A normal solution of a base contains 1 7 grams of replaceable hydroxyl per liter. Fill one burette above the zero mark with a solution of hy- drochloric acid of known concentration. Draw off enough of the acid to remove the air bubbles from the tip and bring the meniscus (curved surface of the water) to the graduated portion of the burette. Burettes are marked in various ways. Notice on those you have, whether each cubic centimeter is numbered, and whether the frac- tions are fifths or tenths of a cubic centimeter. In reading a burette, read from the bottom of the meniscus, using care to have the eye, graduation, and lowest part of the meniscus on the same level. Similarly, fill another burette with the sodium hydroxide solution whose concentra- tion is to be determined and adjust the level of the liquid. Fi s ure 2 Record the readings of both burettes in a table like that given beloiv. Allow about 10 cc. of the sodium hydroxide solution to flow from the burette into an Erlenmeyer flask or into a beaker, and 68 LABORATORY EXERCISES add a drop or two of some indicator, e.g. a solution of phenol- phthalein. What color is produced when phenolphthalein is added to an alkaline solution ? , To an acid solution ? Why is phenolphthalein called an indicator ? Jfopf'.* (i~ '~- $-*. C . Allow the hydrochloric acid to flow, a few drops at a time, into the sodium hydroxide solution, stirring or shaking after each addition, until the reddish tinge just disappears. Now add the sodium hydroxide solution, a drop at a time, until a reddish tinge is produced ; then determine whether a drop of acid will make the solution change. If it will not, continue in the manner indicated until a change of color is produced by a drop or two of either acid or of base. Read the burettes to tenths of a cubic centimeter and record the final readings in the table. Make three separate determinations, washing out the flask after each determination. TABLE Reading, acid burette (before neutralization ) Reading, acid burette (when neutralization is complete) Volume of hydrochloric acid used Reading, base burette (before neutralization) Reading, base burette (when neutralization is complete) Volume of sodium hydroxide used DETERMINATION. 1 2 3 AVER. CONCENTRATION OF A SOLUTION BY TIT RATION 69 Make all calddations on the lower half of the page. From the number of grams of hydrogen chloride in the standard hydrochloric acid used, calculate the weight of hydrogen chloride in the average volume of the acid used. Ans. g. From the equation NaOH + HCl >- + calculate the weight of the sodium hydroxide needed to neutralize the hydrogen chloride contained in the average volume of hydrochloric acid used. Ans. g. From the average volume of sodium hydroxide used, calculate the weight of sodium hydroxide in 1 cc. of the solution tested. 9- Calculate the weight of sodium hydroxide in one liter of this solution. Ans. g. Proceeding as above, you could now make use of the sodium hydroxide solution, whose concentration is now known, to de- termine the concentration of a solution of sulphuric or other acid. The table and calculations would be similar to those already used. CALCULATIONS 70 LABORATORY EXERCISES EXPERIMENT 26 Types of Chemical Change. Direct Combination. Simple Decomposition. APPARATUS. Asbestos mat ; hard glass test tube ; bunsen burner ; electrolysis apparatus (one for entire class) like that shown in Figure 24, consisting of a U-tube provided with two side-arm delivery tubes, and with carbon electrodes ; crystallizing dish, 5 in. ; two 4 in. test tubes ; forceps. MATERIAL. Iodine; yellow phosphorus ; filter paper ; mercuric oxide; hydrochloric acid, concentrated ; wooden splinter ; saturated solution of common salt. Relation of energy to chemical action. Energy is the ability to do work. The more common ways in which it manifests itself are through heat, light, and elec- tricity. Name chemical reactions in which these forms of energy are con- cerned. (0) Direct combination. Put a small, thin piece of yellow phosphorus on a piece of filter paper on an asbestos mat. Phosphorus must be kept under water until the moment of use. It takes fire easily, and its burns are serious. With forceps, lay a crystal of iodine on the piece of phosphorus. Stand well back, as the action is vigorous. Are phosphorus and iodine elements or compounds f ' Complete the equation : __ + I _^PI 3 . / . i Q -'L-I/YI f - v Why is the reaction called a direct combination ? 9J / } * "H ' * J ^ ' * ' '"> J / y~-' i Is energy liberated or absorbed in this reaction f State reasons for your answer. SIMPLE DECOMPOSITION 71 Name three other experiments that you have performed in which elements combined directly without continuous application of heat. state in each case whether, after the action was once started, energy ivas absorbed or liberated. This evidence will guide you in choosing a word to insert in the blank in the statement of the following important principle: Direct combinations take place readily only when energy is () Direct decompositions. Heat a little mercuric oxide in a hard glass test tube. Test for oxygen from time to time. 1 What forms on the sides of the tube ? [tsl/t^S- Write an equation for the reaction. - 3. & + 0^ Wtiy is the action called a direct decomposition Stop heating the mercuric oxide. Does the action continue f Is energy liberated or absorbed in this action ? The instructor should have in operation one or more of the pieces of apparatus like that in Figure 24. In this an electric current is passing through a concentrated solution of hydro- chloric acid. The gas that is given off from the anode is collected over a saturated solution of common salt. What gas is given off at the anode ? At the cathode ? ' 72 LABORATORY EXERCISES Stop the flow of the current. Does the action continue ? Is energy liberated or ab- sorbed in this reaction ? . Write an equation for the re- action. -U&1 -* Ay x Why is it called a direct decomposition ? j : / Figure 24. The evidence of these two experiments will guide you in choosing a word to fill in the blank in the statement of the fol- lowing principle : In most cases of direct decomposition, energy is SIMPLE REPLACEMENT 73 EXPERIMENT 27 - Types of Chemical Change. Simple Replacement APPARATUS. Two test tubes. MATERIAL. Zinc ; dilute hydrochloric acid, 1 to 4 ; fine iron filings ; saturated solution of copper sulphate. (a) Place a piece of zinc in a test tube and add 5 cc. of dilute hydrochloric acid. After the action has continued for several minutes, feel the test tube. Is energy liberated or absorbed in the reaction 9 Write an equation for the reaction. L -uJ^t-e- . ^ 7 ^s^ ^^ C^^ Why is this said to be a case of simple replacement 9 (5) To 8 cc. of a saturated solution of copper sulphate con- tained in a test tube, add 2 cc. of fine iron filings. Close the mouth of the tube with the thumb and shake the solution back and forth several times. After the action has continued a few minutes, feel the test tube. Is energy liberated or absorbed in the reaction 9 Allow the test tube to stand for several minutes. What change takes place in the color of the solution ? J-fstF What change takes place in the^ appearance of the solid 9 s/**> SutcL . *&'ristAJ, & & Complete the equation: CuS0 4 + Fe Why is this called o,ase of simple, replacement 9 From the evidence of the two experiments, choose a word to fill in the blank in the following statement of an important principle : When simple replacements take place, energy is _ -*_. 74 LABORATORY EXERCISES Heats of formation. In the case of most compounds, energy is liberated when the elements unite to form the compound. The amount of energy is known as the heat of formation. In the case of certain com- pounds energy must be furnished, as it is absorbed when the compound is formed. In such a case, the substance is said to have a negative heat of formation. The amount of energy is expressed in calories of heat. A calorie is the amount of heat necessary to warm one gram of water one degree centigrade. The heat of formation is the number of calories of heat absorbed or liberated during the formation of one gram-molecule (a weight in grams equal to the molecular weight) of a compound from its elements. The following table gives the heats of formation of certain compounds. TABLE HEATS OF FORMATION OF CERTAIN COMPOUNDS CALORIES CALORIES Calcium aluminum silicate 1195,550 Magnesium (chloride) (dil. Calcium carbide -6250 sol.) 187100 Carbon disulphide -19000 Magnesium sulphate (dil. Copper (cupric) chloride sol.) 321100 (dil. sol.) 62500 Mercuric chloride (dil. sol.) 50300 Copper (cupric) sulphate Mercuric cyanide -62500 (dil. sol.) 197500 Nitrous oxide -20600 Hydrogen chloride 22000 Nitric oxide -21600 Hydrogen bromide 8400 Phosphorus pentoxide 369400 Hydrogen iodide -7000 Potassium iodide (dil. sol.) 81800 Hydrogen sulphide 4800 Potassium bromide ( dil. sol.) 90400 Iron carbide 8460 Potassium chlorate 93800 Iron (ferrous) chloride Potassium chloride (dil. (dil. sol.) 100100 sol.) 101200 Iron (ferric) chloride Silicon carbide 1963 (dil. sol.) 255700 Silver oxide 7000 Iron (ferrous) sulphate Sodium chloride (dil. sol.) 96900 (dil. sol.) 234900 Sodium iodide (dil. sol.) 70400 Iron (ferric) sulphate Zinc chloride (dil. sol.) 113300 (dil. sol.) 650500 Zinc cyanide -27900 DIRECT COMBINATION 75 Bearing in mind the first principle stated in Experiment 26, pick out from the table five compounds that could easily be formed by direct combination. *t r ame three that could not be firmed Easily by direct combination. In decomposing a compound, exactly as much energy must be furnished as is liberated when the compound is formed. Bearing this fact in mind, and also the second principle stated in Experiment 26, name five compounds that it would be diffictdt to decompose. -/ / , Also name five that would easily be decomposed. rzJ- & would decompose with liberation of energy. . decide whether or not replacement actions will take place, compare the heats of formation of the original compound with that of the one that might be formed in the reaction. What principle will, then, guide you in making your decision ? Of the following equations, complete those whicli you think will actually occur ; in the other cases write the ivords "no reaction." ZriCl 2 4- Cu ^xKBr +CJ 2 NaCl 4-1 CuCl 2 + Mg ^ / HgCl 2 4- Cu ^_ . Verify your conclusions in one or two cases. 76 LABORATORY EXERCISES 1 .EXPERIMENT 28 NW y Types of Chemical Action. Double Decompositions. APPARATUS. Six test tubes. MATERIAL. Solutions of barium nitrate, lead nitrate, silver nitrate, ammonium chloride, sodium sulphate, sodium chloride, copper sulphate (all approximately N/5), sodium hydroxide (1 to 10), dilute hydrochloric acid (1 to 3); solid sodium sulphite, copper sul- phate, sodium carbonate, ferrous sulphide, ammonium chloride. (a) Effect of insolubility of one of the products. To 5 cc. of a solution of barium nitrate, add a little of a solution of sodium sulphate. What evidence is there that chemical action has occurred ? Allow the tube to stand a few minutes. The substance that settles is barium sulphate. Show by completing the following equations what ions are formed by barium nitrate and by sodium sulphate : A' : -y \ + /_ M-J. $o -^ /> "> -jA'"Q i i>anOw 1 - > _ -t- ,:> i .. ] l^ Explain why these actions are reversible reactions. Show by an equation how barium sulphate results on mixing two .solutions. f>C4 ' In this case, is there equilibrium, or an action that goes to an end? ^-^ 4i h ;( - -* fi - - Explain why such an action is called a double decomposition. - DOUBLE DECOMPOSITION 11 The remaining parts of the experiment are intended to illus- trate the conditions under which, on mixing two substances that ionize, we get either an equilibrium or an action that goes to an end. Try the action between solutions of the substances paired in the following table ; record your observations of the results in column 2 ; the information needed for column 5 may be found in the table on page 236 ; fill in the last column after studying the rest of the table as a whole : TABLE SUBSTANCES WHOSE SOLUTIONS ABE MIXED DOES ACTION- GO TO AN END OB REMAIN IN EQUILIBRIUM PR0 8 DU REA8 * F E SO^BLE^R C A 8 CT '^\ INSOLUBLE ? 1^^? (See p. 236) j TO AN END ) 2-\) } s + NaCl Pb(X0 3 ) 2 CuSO 4 + NaOH Pb(N0 3 ) 2 + NaCl- CuS0 4 +NH 4 Cl Complete, the following sentence : A double decomposition will go to an end if one of the possible products is _ _. (&) Effect of volatility of one of the products. In these experiments, use the first-named substance as a solid. Fill the curved bottom of the tube with the substance and add 78 LABORATORY EXERCISES about 2 or 3 cc. of the second compound. Fill in the table as in part (a). Information for column 5 may be found on page 237. TABLE SUBSTANCES USED DOES THE ACTION Go TO AN EN I) ? IONS THAT COULD BE FORMED PKODUCTS POSSIBLE BY NEW COM- BINATION OF IONS POSSIBLE PRODUCTS VOLATILE ? (See p. 237) KEASON IN CASE ACTION GOES TO AN END Na 2 S0 3 + HC1 W- bfrsp (a).' (ft)^> 1 ()S.^ /lST '- ?l -i '-' CuS0 4 + HC1 *p*l' ^/jv (a) (a) *"/ , . < , Na 2 C0 3 + HC1 /p/lSs^i, . $ff (a) (ft) /-/ .;:>y^ //i FeS + HC1 , N, jf^. t/i^f C'^\.n - |"| (a) (ft) (ft) ^ \ f * " it * ' i : M*w_ 3 ' -' (ft) Complete the following sentence : Double decompositions go to an end if one of the possible products is ;.*-/ / . It will be seen from these experiments that a double decom- position goes to an end if one of the products leaves the field of action. If water is found in a double decomposition, it also leaves the field of action, because water does not form ions readily, and therefore is as much out of the action as if it were insoluble or volatile. Explain tvhy a reaction between a base and an acid goes to an end. ff c<*s.*t rj6u. c/t?+ x W&i. ^ JwvJu'^ n SALTS THAT ARE NOT NEUTRAL 79 EXPERIMENT 29 Salts that are not Neutral. APPARATUS. Two test tubes. MATERIAL. Sodium carbonate ; copper sulphate ; ferric chloride ; dilute solutions 'of aluminum sulphate, potassium chToncle T borax. potassium nitrate, zinc sulpnatgj. and ammonium sulphkte-; red and blue litmus papers. ^X^fW^^fL, (a) Fill the curved portion of a test tube with powdered sodium carbonate, Na 2 CO 3 . Add water till the tube is two thirds full and shake it until the sodium carbonate is dis- solved. Into the solution dip a strip of blue litmus and a strip of red litmus paper. Eecord the remit in the tabular form given on page 81. Water is very slightly dissociated into its ions according to the equation: Write the equation for the dissociation^of sodium carbonate. -j/^e<% -* ^wttGTJy - \ i ^~ What four~7cinds of ions are present in the solution ? Complete the following equilibria : ^:_ :' 3 - Carbonic acid has only a slight tendency to ionize, while sodium hydroxide ionizes in much greater degree. Therefore the first of these two actions tends to remove from the solu- tion the H + ions of the water in greater degree than the second tends to remove the OH~ ions. Which of these two ions tends to remain in excess f ^L 0/r" How does this explain the action of sodium carbonate solution on litmus ? 80 LABORATORY EXERCISES The practical effect of dissolving sodium carbonate in water is to form, in slight degree, undissociated carbonic acid and dis- sociated sodium hydroxide. Write an equation showing this. -f /*/. Of what process is the equation the reverse f ( Complete the statement : Sodium carbonate is formed by neutralizing a. /^ (sfro^ig.or weak) acid with a _ X^v^''^? base. Such a salt gives an fyjZ/i (strong or weak) reaction in water solution. Similarly test a solution of sodium tetraborate (borax) with the litmus papers. Record the results in your table. Why would you expect sodium tetraborate to give such a reaction ? (6) In a similar manlier prepare solutions of copper sulphate and ferric chloride, FeCl 8 . Test each with red and blue litmus. Record the results in your table. In each case, name the base formed that has little tendency to dissociate again. Write the equation for the formation of each of these two bases from their ions. What ion is responsible for the litmus reaction obtained? Write the equations showing the combination of this ion with the non- metallic ion of the two salts. Write the equation showing the practical effect of dissolving copper sulphate in water. SALTS THAT ARE NOT NEUTRAL 81 Write a similar equation for the dissolving of the ferric chloride. Of what process is the action in each case the reverse ? Complete the statement: Salts with an acid reaction , are formed by neutralizing a uci j. reaction. SALT ACTION WITH ELITE LITMUS ACTIOX WITH RED LITMFS Sodium carbonate /^^fe^- Copper sulphate /iSr^v Ct*^ $' oL Ferric chloride &uA*t tysJW* At** fit Q&Urt- Ammonium sulpMde H~ LABORATORY EXERCISES 82 EXPERIMENT 30 Flame Tests APPARATUS. Bunsen burner ; three cobalt glass plates. Each solution should be contained in a small bottle or vial with a cork stopper, through which passes a glass tube carrying a platinum, iron, or nichrome wire. MATERIAL. Solutions of salts of lithium, sodium, potassium, calcium, strontium, and barium ; mixed solutions of sodium and potassium salts ; unknowns. (a) Test salts of lithium, sodium, po- tassium, calcium, strontium, and barium. Hold one platinum wire at a time in the hot outer portion of a bunsen flame (Figure 25). Observe the color of the flame in each case. Record result in tabular form. Be careful to replace each wire in its special bottle. TABLE (PART a) Figure 25. SOLUTION FORMULA COLOR OF FLAME The characteristic coloration of the flame in each case is due to the vapor of the metal contained in the compound. (5) Observe the color of a sodium flame through three thick- nesses, of cobalt glass. In a similar way examine the potassium flame through the cobalt glass. FLAME TESTS 83 Record the result of each flame test in tabular form as indicated below. Can you see the sodium Jiame through the cobalt glass 1 What is the effect of the cobalt glass on the potassium fame f Take a solution of a mixture of sodium and potassium salts, and, without using the cobalt glass, note the flame color. Why are not both the characteristic colors seen ? Use the cobalt glass with the mixed solution and find which flame can be recognized. What is the use of the cobalt glass in making flame tests of mixtures of sodium and potassium salts ? What use might be made of the flame tests in analytical work f TABLE (PART 6) SOLUTION COLOB NAKED EYE COLOR COBALT GLASS ( Place about two grams of sodium bicarbonate in a test tube provided with a stopper and a delivery tube that leads into a test tube containing limewater, Ca(OH) 2 .+ ' Heat the bicarbonate without using sufficient heat to color the flame yellow. What collects on the inner ivatt of the test fubgt /r* U j, -* C 4+ KJ v m^^ . &-> +- What produced the change iiYthe limewater? fy The solid left in the test tube is sodium carbonate. A/Qjo 9 How does the taste of the sodium carbonate compare with fKat of the sodium bicarbonate? Complete the equations : H NaHCO 3 (heated) >- Na 2 CO 3 + Ca(OH) 2 + CO 2 ^ CaCO 3 + 86 LABORATORY EXERCISES & ^ EXPERIMENT 33 U| Determination of Water of Crystallization v APPARATUS. Ring-stand with two rings ; pipe-stem triangle ; porcelain crucible ; horn pan balance ; weights ; bunsen burner. MATERIAL. Crystallized barium chloride.. Barium chloride is the salt selected for this determination, because it is easily obtained pure and is neither efflorescent nor deliquescent. Weigh a porcelain crucible on the balance. Then put into the crucible about two grams of crystallized barium chloride, and weigh carefully the crucible and its contents. Record all iveights in a tabular form like that given on page S7. Support the crucible on a pipe-stem triangle so adjusted in height that the bottom of the crucible is a short distance above the top of the inner cone of the bunsen flame. Heat the cru- cible very gently at first. Too rapid heating may cause the water of crystallization to be driven off explosively, carrying along with it some of the salt. Gradually heat the crucible to the full intensity of the flame. After fifteen minutes of this strong heating, slowly cool the crucible, and weigh the crucible and its contents. Record the weight. Repeat the heating and weigh again. Continue this process until you get two successive weighings with the same result. This is called "heating to constant weight." What does this constant weight show about the water of crystalliza- tionf From your data in the table ascertain (1) the weight of the crystal- lized barium chloride, (%} the weight of the anhydrous barium chloride left after heating. DETERMINATION OF WATER OF CRYSTALLIZATION 87 The " anhydrous " salt is the crystallized salt minus its water of crystallization. You know the weight in grams of two substances, crystallized barium chloride and anhydrous barium chloride. These weights are in the same ratio as the molecular weights of these sub- stances. Using the values given in the table of atomic weights (page 234), calculate the molecular weight of anhydrous barium chlorideJBajQl 2 . Make all calculations on page 88. Employing the three quantities that you now know, and representing the molecular weight of crystallized barium chloride by x, form a pro- portion in which, the weights that you obtained by the balance have the same ratio as the molecular iveights of the substances weighed. Solve the proportion in the space marked " Calculations" page 88. Find by subtraction the part of the molecular weight of the crystal- lized salt that is water. How many molecules of water does this weight represent? Write the formula of crystallized barium chloride. . Calculate the percent of water of crystallization in crystallized barium chloride. J~ % f TABLE Weight of crucible + crystallized barium chloride ... Weight of crucible empty Weight of crystallized barium chloride ....... Weight of crucible + barium chloride after Jirst heating . Weight of crucible + barium chloride after second heating Weight of crucible empty Weight of anhydrous barium chloride Molecular weight of crystallized barium chloride . Molecular weight of anhydrous barium chloride Molecular weight of water in crystallized barium chloride Formula of crystallized barium chloride 88 LABORATORY EXERCISES CALCULATIONS -jj? ;'/ }. c^W. ***' *? f ' . Q A *- / z/ , * ' J /> IT -. J ,z // -u ' t~ ~ ^y, },, .4 ^;^ a**y FORMS OF SULPHUR 89 EXPERIMENT 34 Forms of Sulphur APPARATUS. Two test tubes ; watch glass, 2|" ; small iron clamp for use as a test tube holder ; bunsen burner ; magnifying glass ; pan of water. MATERIAL. Roll sulphur ; carbon disulphide ; filter paper, 4" in diameter. (a) Caution ! Carbon disulphide is a volatile liquid that takes fire easily. It should never be used near a flame. Pour 5 cc. of carbon disulphide into a test tube. Add a piece of roll sulphur the size of a pea and shake the tube. Pour the clear liquid into a watch glass, and set it aside to evaporate in a part of the laboratory some distance from a flame. Using a magnifying glass, examine the crystals of sulphur. In the square provided for the purpose make a drawing of a crystal having a symmetrical form. You have recrystallized roll sulphur under conditions that yield separate crystals. Sulphur that crystallizes as you have just observed is called rhombic sulphur. (b) Fold a piece of filter paper as you would to fit a funnel, and lay it aside for future use. Also, have a dish of water ready for use. Half fill a test tube with small pieces of roll sulphur. Carefully melt the sulphur by holding the tube in an inclined position about four inches above a small flame (Figure 26). Rotate the tube slowly while the melting proceeds. What is the color and consistency of the first portion of liquid obtained 9 I 1 Figure 26. 90 LABORATORY EXERCISES This color should be retained during the melting of all of the sulphur. The color should at no time be darker than a light amber. Holding the folded filter paper by the edge, pour the melted sulphur into it (Figure 27). As soon as crystals have formed from the edge to the center of the surface, pour into the water in the pan that part of the sulphur that is still in a melted condition. Im- mediately unfold the filter paper. Make a drawing of one of the more perfect crystals as it is seen under a microscope. This form of sulphur is known as prismatic sulphur. Keep some of the crystals for a few days and then examine them. What changes do you observe ? RHOMBIC SULPHUI PRISMATIC SULPHUR (c) Half fill a test tube with small pieces of roll sulphur, and, holding the test tube with a small iron clamp, raise the tempera- ture of the sulphur until it commences to boil. Meanwhile, tip the tube slightly from time to time and note the important changes that take place in the color and consistency (degree of fluidity) of the sulphur. FORMS OF SULPHUR 91 What changes in the color and consistency of the sulphur did you note from the time it melted until it commenced to boil f !*SL, f ' In the next operation the sulphur will probably take fire. Do not jump. The sulphur will burn quietly. Do not spill it on the desk. Pour the boiling sulphur slowly into cold water, keeping the mouth of the tube moving in a circle so that a thread of sulphur will form in the water (Figure 28). Examine the thread of sulphur. It is the plastic modification of sulphur. What color is it Figure 28. Is it hard or soft ? ?fi - Elastic or brittle f ' Keep it for several days and note any change in properties. Results? 92 LABORATORY EXERCISES EXPERIMENT 35 Preparation of Metallic Sulphides APPARATUS. Test tube ; ring-stand with one ring ; wire gauze with asbestos center ; bunsen burner ; small iron clamp. MATERIAL. Sulphur, powdered ; copper, thin foil or #30 wire ; iron fil- ings, clean and fine enough to pass through a sieve having 60 meshes to the inch ; hydrochloric acid, 1 to 4 ; zinc dust. (a) Fill the curved portion of a test tube with sulphur and heat it to boiling. Insert a strip of thin sheet copper (or fine copper wire) into the boiling sulphur. Result? Withdraw the strip and compare its color, luster, and flex- ibility with the color, luster, and flexibility of copper. Result? M^ What is the name of the compound formed by the combination of copper with sulphur ? Write the equation representing the formation of this compound. (6) Mix thoroughly one part by volume of finely powdered sulphur with two parts of fine iron filings. Put the mixture into a test tube and heat the lower end of the tube just sufficiently to color the flame yellow. When the contents of the tube commence to glow, withdraw the flame. Does the chemical action continue % Why do you think so ? & 1 Break the tube and examine its contents. How does it differ from sulphur in appearance ? PREPARATION OF METALLIC SULPHIDES 93 What gas is produced when hydrochloric acid reacts with iron ? Add one drop of hydrochloric acid to the substance taken from the broken test tube; Cautiously smell of the gas. What evidence is there that the substance taken from the tube is not iron ? Write the equation for thf reaction. * (c) This should be performed by the teacher. Mix thoroughly a pinch of sulphur with an equal bulk of powdered zinc. Placing the mixture in a conical pile on asbestos, and holding the burner at arms length, cautiously ignite the pile from above. Result? .:.' Tf Write an equation for this reaction. hA + llLtt^r ti >$' Compare the action of copper and zinc with sulphur with the action of these metals with oxygen. 94 LABORATORY EXERCISES * 3S EXPERIMENT 36 Preparation and Properties of Hydrogen Sulphide APPARATUS, Five test tubes ; stopper and delivery tube to fit one of the test tubes ; bunsen burner. MATERIAL. Iron sulphide ; dilute hydrochloric acid ; solutions of lead nitrate, cadmium nitrate, and hydrogen peroxide ; litmus paper. (a) In a test tube provided with a stopper and a delivery tube place two or three small pieces of iron sulphide and cover with dilute hydrochloric acid. Complete the equation : FeS + HC1 >- ^ + Collect the gas by downward displacement in a dry test tube, remove the delivery tube, and light the gas in this test tube. What two products are formed when the gas burns in this way? (Examine the tube carefully for traces of moisture before it becomes heated by thejlame of the burning gas.) v //'-, *+ S , /;, ^ ' ,': /^t 6 ' v '- ' How do you identify them ? / 2^,S -f &^~? 3,'ji . What does this show concerning the composition of the gas ? (5) If the gas in the test tube burned quietly, light the gas at the end of the delivery tube. Cautiously smell the gas around the flame. A/ Are all the products formed the same as before ? State the reason for your answer. PROPERTIES OF HYDROGEN SULPHIDE 95 (c) Place the end of the delivery tube in a test tube half filled with water and let the gas bubble through the water two or three minutes. How does the solution taste ? What effect has it on litmus ? Using a small portion of the solution of hydrogen sulphide in each case, add a few drops of : (1) a solution of lead nitrate ; (2) a solution of cadmium nitrate. -0^0 Results? /&**/ Complete tlie H 2 S + Pb(N0 3 ) 2 *- _ + H 2 S The cadmium compound precipitated is used- as an artist's pigment. It is known as cadmium s3-i i Allow the gas from the generator to bubble through a solution of hydrogen peroxide until a decided effect is obtained. Results ? Complete the equation : H 2 S + H 2 2 *._ 1 + __ g- 96 LABORATORY EXERCISES EXPERIMENT 37 Sulphur Dioxide APPARATUS. Flask, 250 cc. with two-hole stopper to fit ; thistle tube ; bent tube with short arms ; bent tube with one long arm ; rubber con- nection tube ; bottle, 150 cc. ; two test tubes.; cover glass; glass stir- ring rod ; ring-stand with one ring and one clamp ; bunsen burner. MATERIAL. Sodium bisulphite ; sulphuric acid, 1 to 1 ; pink carnation ; blue litmus paper ; barium chloride solution, 1 to 20 ; hydrochloric acid, 1 to 4 ; dilute solution of potassium permanganate, three or four small crystals dissolved in a liter of water. i (a) Preparation. Arrange the apparatus as shown in Figure 29. Be sure that the end of the thistle tube is very near the bottom of the flask. Pour 10 grams of sodium bisulphite (NaHSO 3 ) into the flask, then replace the stopper and pour through the thistle tube sufficient water to very little more than cover the end of the tube. Now add sul- phuric acid (1 to 1), a little at a time, until chemical action starts. Other portions of acid are to be added from time to time to Figure 29. cause the reaction to continue. Warm the flask gently, if necessary, to increase the speed of the reaction. Complete the equation : NaHS0 3 + H 2 S0 4 - Na 2 SO 4 (5) Physical properties. Watch the size of the bubbles of gas as they rise through the water in a test tube full of cold water, into which the delivery tube has been inserted, especially after the air in the flask has been displaced. Is sulphur dioxide soluble in water? SULPHUR DIOXIDE 97 Set the test tube' and contents aside for future use, and replace the test tube with the wide mouth bottle (Figure 29). Is sulphur dioxide heavier or lighter than air ? * Why do you think so f Compare the odor of the gas with the odor you observed when you burned sulphur in oxygen, or in air. Result ? $J (c) Chemical properties. Wet a pink carnation and put it in a bottle of sulphur dioxide. Cover the bottle and allow it to stand for a short time. Result ? Touch a piece of blue litmus paper with the end of a stirring rod wet with the liquid left in the test tube. Result ? Why is sulphur dioxide not an acid f An oxide that unites with water to form an acid is an acid anhydride. Is sulphur dioxide such a compound ? Complete the equation : S0 2 + H 2 > U (df) Test for SOr - ions. SO 4 ~~ ions unite with Ba ++ ions to form barium sulphate, a white solid insoluble in water and in dilute hydrochloric acid. This fact is commonly employed in testing for sulphuric acid or a soluble sulphate. 98 LABORATORY EXERCISES Add a drop or two of sulphuric acid to about 10 cc. of water in a test tube, and then add a few drops of a solution of barium chloride. Result t Complete the equation : H 2 S0 4 + BaCl 2 Determine whether the precipitate is soluble in dilute hydro- chloric acid. Result ? (0) Oxidation of sulphurous acid. Add 5 cc. of the water solution of sulphurous acid to an equal volume of a dilute solution of potassium permanganate, KMnO 4 . Result ? To the solution obtained add barium chloride solution and a little hydrochloric acid. Result ? Into ivhat ions did the potassium permanganate convert the S0 3 ions present in the solution ? What term is applied to such a process ? Wfiat element was taken from the potassium permanganate ? Is sulphurous acid a reducing or an oxidizing agent 9 Why? - CuSO 4 Watch the size of the bubbles of sulphur dioxide as they rise through the water in the second bottle. Is sulphur dioxide soluble in water ? Explain. Is sulphur dioxide heavier or lighter than air ? Why do you think so 9 (<0 Chemical properties. Put a wet pink carnation into the safety bottle containing sulphur dioxide. Result 9 PROPERTIES OF SULPHUR DIOXIDE 101 Test the liquid in the second bottle with blue litmus paper. Result ? Write an equation to explain how an add was produced. S6^~t &t^6 -> fiJ-sJi Why is sulphur dioxide an acid anhydride ? What is the name of the acid of which it is the anhydride ? -^^ ^^^/ Add a little hydrogen peroxide to the solution in the second bottle. Pour a little barium chloride solution into the liquid. Result ? Determine whether the product is soluble in dilute hydro- chloric acid. Result ? For what ion have you just tested ? Write the equation for the reaction between sulphurous acid and hydrogen peroxide. s ' Is hydrogen peroxide an oxidizing or a reducing agent f 102 LABORATORY EXERCISES fx 3H EXPERIMENT 39 Properties of Sulphuric Acid APPARATUS. Beaker ; two test tubes ; porcelain evaporating dish ; flask, 50 cc. ; glass stirring rod ; ring- stand with ring and small clamp ; gauze with asbestos center ; bunsen burner. MATERIAL. Concentrated sulphuric acid ; dilute hydrochloric acid ; barium chloride solution, 1 to 20; sodium sulphate solution, 1 to 20; cane sugar ; zinc strips ; fine copper wire or copper gauze ; wood splinter. (a) Action with water. Caution ! In mixing concentrated sulphuric acid with water, the acid should be slowly poured into the water, with constant stirring. The reverse method produces a dangerously explosive spattering. Pour a test-tubeful of water into a beaker. Into this water slowly pour one sixth of a test-tubeful of concentrated sulphuric acitf, .frequently 1 stirring the mixture with a glass rod. Feel the pu.tS'ide- jof .the ^aker.. noticeable 'effect Is produced ? Keep for parts (6) and.(cT) the dilute sulphuric acid just prepared. () Action with metals. Put a zinc strip into one sixth of a test tube of concentrated sulphuric acid. Is there much action between the zinc and the concentrated sulphuric Ponr the contents of the test tube into the sink and wash down the acid with water. Rinse off the zinc strip and return it to the test tube. Then pour upon it some of the dilute t sulphuric ticid made in part (a). Describe the action. PROPERTIES OF SULPHURIC ACID 103 Name the gaseous product, mid write the equation for the reaction + x^ -> I ^y -t How does dilute sulphuric acid differ from the concentrated acid in its action u:ith metals 9 / Place some copper wire gauze or a small loosely rolled ball of tine copper wire in a small flask, and add a fifth of a test tube of concentrated sul- phuric acid. Support the flask on an asbestos gauze on a ring-stand in a hood, and loosely clamp the neck of the flask (Figure 31). Heat the flask carefully with a small flame until action commences. Then remove the flame. Figure 31 Describe the action. Cautiously smell the gaseous product. What is it f &>r^ Wiat gas is usually liberated ivhen an acid reacts ivith a metal f Remembering that hot, concentrated sulphuric acid acts as an oxidizing agent, explain why we do not get this gas here. Fro,,, which ofthr nr!-__ _ + _ Mercury and silver react similarly to copper with hot con- centrated sulphuric acid. Write the equation for the reaction in the case of silver. ( Complete the statement : When sulphuric acid acts as a dehydrating agent on com- pounds, it removes from them / M ?- Add dilute hydrochloric acid to the precipitated barium sulphate. Result? Using barium chloride solution and dilute hydrochloric acid, repeat the test with dilute sulphuric acid,'ftydrogen sulphate. Result? . . '4L State the test for a sulphate. toJb bss- trt<**$-%t^ DRAWING, PART (&) < 106 LABORATORY EXERCISES EXPERIMENT 40 Preparation of Nitrogen APPARATUS. Pneumatic trough ; phosphorus stand (Figure 32) consist- ing of (a) cork to fit hole in shelf of trough ; (ft) # 16 copper wire; and (c) blackboard crayon ; iron forceps ; stirring rod ; burner ; wide-mouth bottle, 8 oz. ; glass plate. MATERIAL. Small piece of phosphorus kept under water ; filter paper ; wooden splinter. Hollow a cavity in the end of a piece of blackboard crayon. Place it on the wire stand. (J, Figure 32) and insert cork in the hole in the shelf of a pneumatic trough. Fill the trough with water to 1 cm. above the shelf. Have close at hand an 8 oz. wide-mouth bottle. Caution ! Yellow phosphorus should never be handled except under water. With a pair of forceps, take a piece of phos- phorus about half the size of a pea, remove the adhering water with a bit of filter paper, and place the phosphorus in the hollow of the crayon. Touch the phosphorus with a warm stirring rod and immediately invert over it the wide-mouth bottle, and let it rest on the shelf of the trough. Carefully note and record the results. Figure 32. o, cork ; b, # 1 6 copper wire ; When the white cloud in the bottle has cleared, press the phosphorus stand from below up into the bottle. Slide the bottle to the edge of the shelf and allow the phos- phorus stand to drop down into the trough. Cover the mouth of the bottle with a glass plate, invert it, and set it on the desk. A. PREPARATION OF NITROGEN Describe the appearance of the nitrogen. a lighted splinter into the bottle. 107 Result? \g)j^^ What constituent of the air was removed by the phosphorus? WJiat other constituents still remain with the nitrogen ? &$Jt~ sfLsO^JL -*''t' x ^ to 0(s&^* - Dispose of the phosphorus stand as directed by the instructor. Alternative Method APPARATUS. Pneumatic trough ; two wide-mouth bottles; glass plate; ring-stand with one ring and one clamp ; 250 cc. Erlenmeyer flask with two-hole rubber stopper to fit ; thistle tube ; delivery tube ; wire gauze with asbestos center ; bunsen burner ; test tube. MATERIAL. Sodium nitrite, NaN0 2 ; ammonium chloride; wooden splinter. Put 15 grams of sodium nitrite and 10 grains of am- monium chloride into a 250 cc. Erlenmeyer flask. Fit the flask with a two- hole rubber stopper carrying a thistle tube and a delivery tube leading to a pneumatic trough. Support the flask on a wire gauze resting on the large ring of a ring-stand (Figure 33). Add a test-tubeful of tube. Figure 33. the *lask through the thistle these two as ^ 108 LABORATORY EXERCISES Caution ! ! Avoid overheating the flask, so as to prevent an explosive de- composition. Gently heat the flask so that the nitrogen will be evolved at a temperature considerably below the boiling point of water. In case frothing occurs from overheating, pour a few cubic centimeters of cold water into the thistle tube. After the air has been displaced from the flask, collect the nitrogen in wide-mouth bottles. Lower a lighted splinter into a bottle of nitrogen. Result ? <.// Has the nitrogen of the air an odor 9 Smell a bottle of the nitrogen collected. What does this result show about the nitrogen collected f The nitrogen in the present experiment results from the decomposition of ammonium nitrite. This compound is so unstable that it is freshly prepared by the interaction of ammonium chloride and sodium nitrite. Complete the equations : NH 4 C1 + NaN0 2 >- NH 4 NO 2 + _ NH 4 NO 2 ^ +' DRAWING PREPARATION AND PROPERTIES OF AMMONIA 109 EXPERIMENT 41 Preparation and Properties of Ammonia APPARATUS. Ring-stand; clamp; test tube rack; three test tubes, one fitted with one-hole stopper and delivery tube ; perforated card- board square ; bunsen burner ; enameled pan. MATERIAL. Slaked lime; ammonium chloride; ammonium sulphate; sodium hydroxide solution ; red and blue litmus paper. (a) Preparation of ammonia. Take a little ammonium chloride in one hand and in the other a little slaked lime (dry). Smell of each. Rub the two to- gether between the palms of the hands. Smell the mixture cautiously. Bring a moist strip of litmus paper near t mixture. Results? #UA*U ft ' (>) Repeat, using ammonium sulphate and slaked lime. As before, smell, and apply litmus test. Results? (c) To a little sodium hydroxide solution in a test tube add a small amount of ammonium chloride. Heat gently, smell cautiously, and test with litmus as before. Results ? Ammonium chloride, NH 4 C1, and ammonium sulphate, (NH 4 ) 2 SO 4 , are salts. Regarding the reaction between sodium hydroxide and ammonium chloride as a double replacement, name the two products formed. . ttydsurj^tl ^WeU^n^ wUk^' Write the equation showing these two as products. i .^& 110 LABORATORY EXERCISES Ammonia gas, NH 3 , results from the decomposition of one of the products. Write the equation for this decomposition. Complete the equation for the action in part (a). Ca(OH) 2 +2NH 4 Cl ^_ _ + Write a single equation for the action in part (b). How could you prove that a substance given you ivas an ammonium salt ? 1 TL /,- **./JAAA-i /'*,?< \ 2^4 -^/& Mjt '.ifrWw -nr,l< (c?) On a piece of paper, mix a quarter of a test-tubeful of ammonium chloride with a quarter of a test-tubeful of slaked lime. Put the mixture into a test tube provided with a delivery tube for the collection of the gas by upward displacement (see Figure 34). Warm the mixture very gently. Fill a. dry test tube with the gas. Figure 34. ) Properties of ammonia. What is the color of the ammonia gas ? 'l Is this gas lighter or heavier, than air 9 (/) Place a test tube of ammonia mouth downward in a dish of water. Result? What does this show 9 ft v ' AMMONIUM COMPOUNDS 111 EXPERIMENT 42 .* Ammonium Compounds APPARATUS. Test tube with stopper and single-bend delivery tube; four other test tubes ; ring-stand with one clamp ; bunsen burner. MATERIAL. Ammonium chloride ; slaked lime ; concentrated hydro- chloric acid ; concentrated sulphuric acid ; sodium hydroxide solution, 1-10 ; red litmus paper ; blue litmus paper ; labels. On a piece of paper, mix thoroughly 5 grams of ammonium chloride and 10 grams of dry, slaked lime. Notice the char- acteristic odor of ammonia. Place the mix- ture in a dry test tube, provided with a stopper and delivery tube. Clamp it in a nearly horizontal position with the delivery tube pointing down (Figure 35). Have at hand three test tubes : (a) a dry test tube to which 2 drops of concentrated hydrochloric acid have been added ; (6) a test tube con- taining 1 drop of sulphuric acid ; (- NH 4 OH heated -+ NH 4 C1 + Ca(OH) 2 >- Having performed the test for ammonia on these four samples, how could you now tell whether the original material was a chloride or a sulphate ? PREPARATION AND PROPERTIES OF NITRIC ACID 115 EXPERIMENT 43 Preparation and Properties of Nitric Acid APPARATUS. Retort, 100 cc. ; two test tubes ; battery jar; ring-stand with large ring ; wire gauze with asbestos center ; clamp ; bunsen burner ; funnel or thistle tube ; flask. MATERIAL. Sodium nitrate ; concentrated sulphuric acid ; concentrated hydrochloric acid ; ferrous sulphate solution, freshly prepared; copper strip; excelsior; unknowns. Caution ! Concentrated sulphuric and nitric acids are dangerous to both flesh and clothing. (tf) Preparation. Put about 15 grams of sodium nitrate into a tubulated retort. Place the retort on a wire gauze. Insert the neck of the retort as far as possible, but not tightly, into a flask partly immersed in water (Figure 36). Clamp the retort in position and pour 10 cc. of concen- trated sulphuric acid through a funnel, or thistle tube, upon the nitrate. Replace the stopper and heat the contents of the retort gently. Be careful not to allow the flame to pass through the gauze. What two changes of state Figure 36. take place in the distillation of the acid? Distil, using moderate heat, as long as any nitric acid runs down the neck of the retort. Allow the retort and its contents to cool without removing the retort from the stand. 116 LABORATORY EXERCISES Complete the equation : Why does this reaction go to an end f A-J /WPiitt'i (&*> Upon what characteristic of sulphuric acid does its use in this experiment depend f ^ C i '-i '.- / (6) Oxidizing action of nitric acid. N.B. The acid collected is much more active than the ordinary nitric acid. Use it very carefully and throw all solid materials in a waste jar immediately after examining them. Put into a test tube 1 cc. of the acid that you have pre- pared, and thrust in a small, loose plug of excelsior so that it remains about an inch above the acid. Hold the test tube by means of a holder and heat the acid until it boils vigorously, and the vapor reaches the excelsior. After a moment, hold the tube so that the flame is directly under the excelsior for a few seconds. -* \ J /V / Results ? ^ /# x'l/7 f.t A /'( / ^"/>V i ' ' - v*? ** This action is chiefly due to the very strong oxidizing char- acter of nitric acid. Fill the curved bottom of the test tube (1 cc.) with the acid you have prepared. Add twice the volume of hydro- chloric acid and heat the mixture. What change in color takes place ? Smell cautiously the gas issuing from the test tube. What is this gas ? frt*- PREPARATION AND PROPERTIES OF NITRIC ACID 117 Complete the equation : , HNO S + .3 HC1-W// fl + 3'fs.. +NO Explain how this shows the oxidizing power of nitric add. Such a mixture of nitric and hydrochloric acids is known as aqua regia. ((?) Action of nitric acid with metal. Put a small strip of copper into a test tube and add a few drops of the acid that you have prepared and a few drops of water. Result ? Supposing that hydrogen is at first formed, as in the typical action of an acid with a metal, what further action would occur as a result of the property of nitric acid shown in part (b) 6 . Dissolve a very small amount of sodium (or potassium) nitrate in 2 cc. of water. Add an equal volume of ferrous sulphate solution. Hold the tube in an inclined position, and pour slowly down the side of the tube 2 cc. of concentrated sulphuric acid. The heavy acid will run down the tube and form a separate layer under the mixture of the other two solutions. Describe the appearance between the two layers. j &l& This is a very delicate indication of a nitrate. Repeat the test once or twice using unknown solutions furnished by the instructor. Record the results obtained with the unknown solutions. 118 LABORATORY EXERCISES EXPERIMENT 44 Preparation and Properties of Nitric Oxide APPARATUS. Four wide-mouth bottles (6 to 8 oz.) ; 2-hole rubber stopper to fit wide-mouth bottle; thistle tube; delivery tube; pneumatic trough or dish; oxygen generator, consisting of wide-mouth bottle (6 oz.), with a 2-hole rubber stopper carrying a delivery tube and a funnel having a glass rod with one end ground into the funnel so as to form a stopper (Figure 37) ; test tube. MATERIAL. Copper (wire, rivets, or turnings) ; concentrated nitric acid; sodium peroxide. (a) Preparation. Arrange a wide-mouth bottle with a stopper carrying a thistle tube and delivery tube. Place in the bottle about 10 g. of copper and cover with a test-tubeful of water. Pour about one third of a test-tubeful of concentrated nitric acid through the thistle tube of the generator and wait for the action to start. Collect the gas by the displacement of water. To maintain the action in the generator, add from time to time small quantities of the concentrated nitric acid. .Note the color of the gas that first appears in the generator, /v Why does it not appear in the collecting bottle ? What is the difference in color between this gas and the one that does collect in the bottle 9 The gas that collects in the bottle over water is nitric oxide, NO. Collect one full bottle, and another bottle half full of the nitric oxide, and let them stand in the trough for use later. Note the color of the liquid in the generator. This color is characteristic of the water solution of cupric salts. What gas is often produced by the action of an acid with a metal ? PREPARATION AND PROPERTIES OF NITRIC OXIDE 119 What oxidizing action prevents our getting this gas here? Name the product that is formed instead. \ The removal of oxygen from certain nitric acid molecules results in their reduction to nitric oxide and water. Complete the equation : 3 Cu + 8 HN0 3 >- Cu(N0 3 ) 2 + (b) Action with oxygen. Obtain from the instructor one of the bottles for generating oxygen (Figure 38) by the action between water and sodium peroxide : 2 Na 2 O 2 + 2 H 2 O >- 4 NaOH + O 2 Gently loosen the stop- per in the funnel so as to allow a few drops of the water in the funnel to fall upon the sodium peroxide at the bottom of the generator. Allow the air in the delivery tube to be dis- placed by the oxygen. If the action stops, let another drop of water fall on the peroxide. Figure 38. Caution! To avoid violent action, use water in small amounts with intervals between. 120 LABORATORY EXERCISES Pass oxygen, a little at a time, by means of the delivery tube, into the bottle that is half full of nitric oxide, which is stand- ing in the pneumatic trough. What are the two noticeable results ? In what respect does this colored gaseous product differ in compo- sition from the nitric oxide? Complete the equation : 2 NO + Q 3 >- ^/ / (tf) Action with air. Allow the full bottle of nitric oxide to escape into the air. What evidence of a chemical change do you observe ? ' ^k-4* 5- - MnSO 4 + ft- _ + _ Show by an equation how the two temporary products that you have crossed out react with each other : //& +6 -> . tt b + ^i Show the Jinal products of the reaction by completing the following equation : KBr + Mn0 2 + H 2 SO 4 >- lA^MxC ' y (6) Solubility of bromine. Add a few drops of carbon disulphide to a test tube one third full of water, and shake the contents. Are the two liquids miscible: that is, are they completely soluble in each other ? J{# To what extent is bromine soluble in water 9 ( /Mf /, . > Show the Jinal products of the reaction by completing the following equation : KI + MnO a + t.H 2 S0 4 ^^J 1+4 . 4r2: - + -" PREPARATION AND PROPERTIES OF IODINE 127 (6) Effect of various solvents on iodine'. With a splinter remove small portions of the solid that ad- heres to the sides of the tube, and try to dissolve the iodine in (1) water, (2) alcohol, (3) a water solution of potassium iodide, (4) carbon disulphide (or chloroform). Record your results in a tabular form: TABLE SOLVENT COLOR op SOLUTION DEGREE OP SOLUBILITY (Slightly, moderately, or very) (e) Carbon disulphide test for iodine. Put 3 cc. of water and a very small crystal of iodine into a test tube ; into another test tube put an equal volume of a solution of potassium iodide. To each test tube, add a few drops of carbon disulphide (or chloroform). Shake each mixture thoroughly. In which case does the carbon disulphide acquire a color ? &* /*/ /t^. ^o-friv*-** * What is the color ? f^r^r^J^ ' In what state must the iodine be to give the test with carbon disul- phide ? (c?) Replacement of iodine by other halogens. To about 3 cc. of a very dilute solution of potassium iodide, add a few drops of chlorine water. Result f 128 LABORATORY EXERCISES Add chloroform (or carboh disulphide) and shake the mix- ture. Result ? Complete the equation : Ki + cu-^AV+ .7. To another portion of potassium iodide solution, add bromine water and chloroform. Shake the mixture. Result f L . &/ L/' Complete the equation : * KI+Br 2 ^JS_ + Under what conditions does one element replace another 9 (See Experiment 27 and the table it contains.) . j^J^ c_ \n( tf tUW--t ^ (5) To 1 gram of potassium bromide in a test tube, add a few drops of concentrated sulphuric acid. Warm gently, if neces- sary. Result? -^ 130 LABORATORY EXERCISES Test the gas with moist litmus. Result ? Complete the equation : NaBr + H 2 S0 4 ^Na a SO 4 What is the color of the gas in the test tube 9 /., Wfiat element gives this color and what does it indicate as to the stability of the hydrobromic acid 9 Smell the gas very cautiously. you detect the odor of sulphur dioxide ? Of what acid is sulphur dioxide the anhydride ? What name is given to the process by which sulphuric acid is con- verted into sulphurous acid 9 : ^^tn^ Complete the equation : ' H 2 SO 4 + 2HBr ^H 2 SO 3 + _ _+_ / . -v X } 1 f f\ ^*) ""^ / /\ Where did the free bromine come from in this experiment 9 (e) To 1 gram of potassium iodide in a test tube add a few drops of concentrated sulphuric acid. Test the gas with litmus and determine amount of fuming, as before. Results 9 What do these results show about the amount of hydriodic acid issuing from the tube ? THE HALOGEN ACIDS 131 Compare the stability of this acid with that of hydrobromic acid. Smell the gas cautiously. Result f teolterti*"^ Wliat process would form hydrogen sulphide from sulphuric, acid f State how this is accomplished by the hydriodic acid, accounting for the production of the iodine at the same time. (Compare with action of sulphuric acid on potassium bromide.) DW-M Complete the equations: 8NaI+ if H 2 S0 4 + 8 HI ; Which of these three halogen acids is most stable ? l^L* Which has the greatest heat of formation (see table below) ? ' Which is the most easily oxidized by sulphuric acid f Give a reason for your last answer. fit&ehxsvt^ - / 7- HEATS OF FORMATION OF THE HALOGEN ACIDS Hydrochloric acid Hydrobromic acid Hydriodic acid + 22,000 calories 4- 8,400 calories 7,000 calories 132 LABORATORY EXERCISES EXPERIMENT 49 Destructive Distillation APPARATUS. Hard glass test tube ; two sets of stoppers and delivery tubes, as shown (Figure 41 ); two 8 in. test tubes ; ring-stand ; clamp ; bunsen burner. MATERIAL. Wood (splinters) ; soft coal ; litmus paper. (a) Destructive distillation of wood. Arrange apparatus as shown (Figure 41), having the lower end of the delivery tube half an inch from the bottom of the condensing tube. Fill a hard glass test tube with splinters of wood. Heat, gently at first and then strongly, until no further change can be noted. Describe the appearance of the volatile matter passing off from the wood. * \j C! " l/ 'V '" While heating, bring a flame to the end of the jet tube. Result f Figure 41. What is the substance found there ? When the action is complete, allow the apparatus to cool, then examine the contents of the test tube. J .c/ How does it differ from the original wood ? 9 /'ifr. DESTRUCTIVE DISTILLATION 133 What is the appearance of the substance in the condensing tube ? / Describe any distinct layers that can be distinguished. ^S^V <&t<&t,l idt ' Test the liquid in the condensing tube with litmus paper. Result ? ,&xA^ Note the odor of the liquid. & This tarry distillate is a mixture called pyroligneous acid. It contains wood alcohol, acetic acid, acetone, tar, and other substances. The decomposition by means of heat of a complex substance such as wood, into simpler substances, some of which are con- densed to liquids, is called destructive distillation. Name three direct products of the destructive distillation of wood. (5) Destructive distillation of coal. Free the hard glass tube from charcoal, and half fill it with finely crushed soft coal. Replace the condenser and tubes with a fresh set, and heat as before. Describe the appearance of the volatile matter in this case. / es,\*jL - - /^y-tfov-CsC* Is it the same as that obtained from the wood ? While the heating is going on, lay a piece of red litmus paper over the end of the jet tube. Result ? What kind of a compound is shown to be present by this test ? ' 134 LAB OR A TOR Y EXER CISEti Bring a flame to the end of the jet tube, Result ? Heat the tube until gas is no longer given off. Then allow the tube to cool. When you can handle the hard glass tube, pour its solid contents on the base of- the ring-stand. Describe the residue as to color, structure, and weight, as compared ivith the original coal. This residue is coke. Examine the condensing tube. Describe the liquid deposited there. Jjrfipw ts^tU-i^A-^ Mt&t- ' t sUyUt M (>drvv<~ I Why is the distillation of soft coal a destructive distillation ? Name three direct products of this destructive distillation. DRAWING PROPERTIES OF CARBON 135 EXPERIMENT 50 Properties of Carbon APPARATUS. Hard glass test tube, 6", with one-hole stopper and bent delivery tube ; two test tubes ; beaker, 200 cc. ; evaporating dish ; funnel ; ring- stand with clamp, and one ring to support the funnel ; stirring rod ; bunsen burner ; small sheet of paper. MATERIAL. Copper oxide, powdered ; charcoal, powdered ; limewater ; boneblack ; sugar ; copper sulphate solution, 1 to 40 ; filter paper ; cider vinegar. (a) Carbon as a reducing agent. Arrange the apparatus as shown in Figure 42. Fill one- tenth of a test tube with copper oxide, then pour the oxide on a sheet of paper. Using the same test tube, measure an equal volume of powdered charcoal. Add the charcoal to the copper oxide on the piece of paper, and mix the two thoroughly. -Pour the mix- ture into the hard glass test tube shown in the figure. Pour limewater into the test tube into which the delivery tube extends until the lime- water just touches the end of the delivery tube. Heat the hard glass test tube, cautiously at first, com- mencing at the part around the upper portion of the mix- ture, and gradually moving the flame toward the closed end of the tube. Figure 42. What change do you observe in the limewater at first ? ' ' 136 LABORATORY EXERCISES Carbon dioxide is the anhydride of carbonic acid. Complete the equation : What base is in solution in limewater ? 1 / // :-&/..: 4 / Write the equation for the neutralization of this base with carbonic ' acid - &> ^ w 2. j Allow the tube to cool, and when cold pour its contents into a 200 cc. beaker. Let a small stream of water flow into the beaker. II r -fit What substance is carried away by the water f What is left in the beaker 9 What element is taken from the copper oxide f Complete the equation : CuO+ C ^_ ^ + ^ /-* What name is given to the process of removing oxygen from a . compound ? , What kind of an agent is carbon in this case f (5) Carbon as a decolorizer. Thoroughly mix a little boneblack with some cider vinegar in an .evaporating dish. Fold a sheet of filter paper and place it in the funnel. Pour boneblack on the filter and scoop out a hollow in the center of the boneblack. Into this hollow, pour the mixture of vinegar and boneblack. Collect the fil- trate and note its color. Result? Put enough sugar into a test tube to fill the rounded part. Heat this slowly and evenly, rotating the tube as the sugar melts. The sugar should be well browned, but not burned. The product contains caramel, a substance used as a flavor in PROPERTIES OF CARBON 137 cooking. As soon as the tube containing the caramel has cooled, fill two thirds of it with water, and warm the mixture until the solid has dissolved. The solution thus obtained is used to illustrate the impure sugar solution of a sugar refinery. The heat used in obtaining crude sugar helps to give the product a brown color which must be removed to get white sugar. Filter the solution of sugar and caramel as you did the cider Filter a dilute solution of copper sulphate through bone- black. Result? /Zf> ^L^VV^A Can the color be removed from all liquids by filtering them through boneblack? DRAWING 138 LABORATORY EXERCISES EXPERIMENT 51 Preparation and Properties of Carbon Dioxide APPARATUS. Wide-mouth battle, 8 oz., with two-hole rubber stopper to fit, carrying thistle tube and delivery tube ; three wide-mouth bot- tles ; three test tubes ; glass tube ; enamelled ware dish or pneumatic trough ; three glass plates. MATERIAL. Marble chips ; concentrated hydrochloric acid ; limewater ; blue litmus solution ; candle ; wood splinter. Figure 43. (a) Preparation. Into a bottle provided with a delivery tube and a thistle tube reaching nearly to the bottom of the bottle, put marble chips to about the depth of an inch. Cover the marble with water, and add concentrated hydro- chloric acid, a few cubic cen- timeters at a time, so as to get a moderate action. Collect three bottles of the gas by the displacement of water (Figure 43) for use in parts (#), (5), , and (e). Describe the action in the generator. Complete the equation: CaCO * HC1 Write the equation for the decomposition of carbonic acid. Represent the entire action by one equation. , -f iktt-^&Alii ^r *. Is carbonic acid stable at ordinary temperatures ? PREPARATION AND PROPERTIES OF CARBON DIOXIDE 139 Why can any of the common acids be used in preparing carbon dioxide ? . (5) Odor and color. Inhale some of the gas from a bottle. WJiat is the effect of the gas on the nose ? Has carbon dioxide color ? (e) Solubility. Let the gas from the generator bubble through a test tube half full of blue litmus solution. What change takes place ? J?-/ (If the result is not evident to you, compare the color of the liquid in the test tube with that of the litmus solution in the stock bottle.) Why is carbon dioxide called an acid anhydride ? Write the equation for the reaction of carbon dioxide with water. ' What does the method of collection shoiv in regard to the extent to which carbon dioxide is soluble in water ? ^^frCsfrfM How is the solubility of the gas increased in the preparation of effervescent drinks ? (Class discussion.} $ . \ ,_ 7 g Relative weight and relation to combustion. Slowly invert a bottle of carbon dioxide over a lighted candle. Results? -^^; What, three properties of carbon dioxide are shown Vt/t-Q' 140 LABORATORY EXERCISES (e) Action with limewater. Pour half a test-tubeful of limewater into a bottle of carbon dioxide and shake the bottle. Result t / Write the equation to show the formation of the precipitate, calcium carbonate. &&(OI4) r/- 7 60- ^^^ **t~ (/) Product of combustion. Burn a wooden splinter in a bottle of air. Add limewater and shake the bottle. Result f How does this show that the splinter contains carbon ?. * Blow through a glass tube into a test tube half full of lime- water. EesuU? '; ./:,-x, What gas do we exhale 9 o /-;' How is it produced in the body ? ' CHEMICAL FIRE EXTINGUISHER 141 EXPERIMENT 52 Chemical Fire Extinguisher APPARATUS. Four test tubes, 6" ; one-hole rubber stopper to fit test tubes and carrying a delivery tube ; wide-mouth bottle, 6 oz. ; test tube, 4" x y ; one-hole rubber stopper to fit 6 oz. bottle ; glass tube 4" long ; glass tube 2" long drawn out so as to deliver a stream 2 mm. in diameter; 2' of rubber tubing to fit glass tubes; bunsen burner ; ring- stand with small clamp ; pan. MATERIAL. Limewater ; sodium bicarbonate ; sulphuric acid, 1 to 10; splinters of wood. (a) Pour 15 cc. of limewater into a test tube and set it aside for future use. Close the mouth of another test tube with a one-hole rubber stopper carrying a delivery tube. Arrange the apparatus so that the delivery tube will dip into the lime- water in the first test tube. Pour into the test tube generator enough sodium bicarbonate to fill the curved portion of the test tube ; add about 10 cc. of water and a few drops of sulphuric acid, then immediately replace the stopper. What is the name of the gas evolved ? Complete the equation : 2 NaHC0 3 + H 2 S0 4 >- + ; + _ (&) Arrange the apparatus as nrpart (a), using a dry test tube for the generator. Pour into the test tube generator about 5 cc. of sodium bicarbonate and heat it until the flame in con- tact with the test tube turns yellow. This indicates that the glass is beginning to soften. Continued heating would melt the glass. What change takes place in the limewater ? What collects on the cool portion of the tube f 142 LABORATORY EXERCISES What are two of the substances produced by the decomposition of sodium bicarbonate ? Complete the equation : 2 NaHCO 3 Figure 44. Why is sodium bicarbonate the chief ingredient of dry-powder Jire extinguishers ? (c) Arrange apparatus as shown in Figure 44. Pour a nearly satu- rated solution of sodium bicarbon- ate into the wide-mouth bottle until the surface of the liquid reaches the curved portion of the bottle near its neck. Fill the small test tube with very dilute sulphuric acid (1 to 10) and stand the test tube in the bottle. Replace the stopper and set the bottle on the table. Build a small fire of splinters of wood in a pan placed in a sink, or wherever tha instructor may direct. Hold the stopper of the fire ex- tinguisher firmly pressed into the mouth of the bottle (Figure 45); point the end of the Figure 45. delivery tubeat the fire, and invert the bottle, fire. Put out the CHEMICAL FIRE EXTINGUISHER 143 What gas was generated by the reaction between the sodium bicar- bonate and the sulphuric acid ? Why was the liquid forced out of the bottle ? /- L^ What two advantages are there in using more than enough sodium bicarbonate to neutralize the sulphuric acid ! Piw 144 LABOEATOEY EXEECISES r~ v h7 EXPERIMENT 53 Hard Waters APPARATUS. Carbon dioxide generator, consisting of wide-mouth bottle with two-hole stopper to fit, carrying thistle tube and delivery tube for leading gas to the bottom of a test tube ; four test tubes ; small funnel ; stirring rod ; bunsen burner. MATERIAL. Calcium sulphate (plaster of Paris) ; magnesium sulphate ; marble chips ; dilute hydrochloric acid, 1:4; limewater ; distilled water ; filtered soap solution ; filter paper. (a) Add a drop or two of soap solution to distilled water in a test tube and shake the tube. Are lasting suds produced ? This result is characteristic of " soft " waters. Drop a pinch of magnesium sulphate into a test tube two thirds full of water. Close the mouth of the tube with the thumb and shake it thoroughly. Add a few drops of the soap solution. Shake the tube. Do suds form ? What is produced f flu n^ * { Ca HARD WATERS 145 formed to the bottom of a test tube two thirds full of lime- water. Otfu(j?/fj^ What is the first Result f The insoluble compound formed is calcium carbonate. Write the equation for its precipitation. // , /% What happens to the precipitate on the continued passing of the carbon dioxide ? ^2^y O^n. OL^< Qf. fy> . The compound formed is calcium bicarbonate, 7s it soluble or insoluble ? What acid was formed when the excess of carbon dioxide reacted with the water in the test tube ? /&. 6- o (l/fa/d^W*^ 0~4JLA What effect did this acid have on the precipitate, calcium carbonate ? Complete the equation : ,0. A>1^ /) t*L /] ft*. If /ft /) \ CaCUo -f- '.- i. ^4- '^ U > Y 3-t , ; -r 2T^- (c) Pour a little of the water solution of calcium bicarbonate into another test tube. To this portion, add a few drops of soap solution and shake the tube. What kind of water is the water containing calcium bicarbonate in solution? >' ; y . .sfifrs^uu X/'r^ 4s*^ *rW**J. In a separate test tube heat gently another portion of t calcium bicarbonate solution. What: happens on warming the liquid, particularly near the watts of the test tube? / x Hold a stirring rod with a drop of lime water on its end above the heated liquid in the test tube. What is the effect on the limewater ? *+&*-* ^^ 146 LABORATORY EXERCISES What does this show ? <& Continue heating the liquid in the test tube until it boils. What is the second effect of heat on a woJer solution of calcium bicarbonate ? b A 'V; A" , Y ,'t'X'W *!.< sff'fv' ^// Filter the contents of the tube just heated. Test the filtrate with a few drops of soap solution. Has the water solution of calcium bicarbonate been softened ? Explain. Such a hard water is called a "temporary" hard water. Complete the equation for the softening of a temporary hard water by boiling: CaHjCCOi), *-< Account for the crust formed on the inside of tea kettles in tvhich temporary hard water is boiled day after day. (d) Add a pinch of calcium sulphate (plaster of Paris) to a test tube two thir'ds full of water. Shake the tube, filter the contents, and divide the filtrate into two portions. Using one, determine with soap solution whether or not the water is hard. Kesult? Boil the second portion, and then test with soap solution. ut ^$fy,.f' * J//tyA''y^S' Is the water solution of calcium sulphate softened by boiling ? / HARD WATERS 147 Such water is "permanent" hard water. Would permanent hard water form a deposit on a teakettle f*& Explain, c^i j/j M&frW&CSCt A water often contains both temporary and permanent hard- ness. How could you show the presence of each kind of hardness in the presence of the 148 LABORATORY EXERCISES EXPERIMENT 54 Baking Powders APPARATUS. Four test tubes ; rubber stopper, one-hole, to fit test tube and carrying a delivery tube as shown in Figure 46 ; test tube rack. MATERIAL. Sodium bicarbonate ; limewater ; hydrochloric acid, 1 to 4 ; potassium acid tartrate ; monocalcium phosphate ; monosodium phosphate ; sodium alum ; blue litmus paper. (a) Reaction between sodium bicarbonate and acids. Arrange apparatus as shown in Figure 46. Pour about 10 cc. of limewater into the test tube into which leads the long arm of the delivery tube. Remove the stopper and put a pinch of sodium bicarbonate (baking soda) in the tube ; add a few drops of dilute hydrochloric acid and immediately replace Figure 46. t h e stopper. What gas is liberated by the reaction ? Write the equation representing the reaction. Sour milk contains lactic acid, H(C 3 H 5 O 3 ). Why is a mixture of sour milk and baking soda used as a leaven- ing agent? Equation ? (5) Cream of tartar baking powders. Sprinkle a few particles of cream of tartar, potassium acid tartrate, KH(C 4 H 4 O 6 ), on a dry piece of blue litmus paper. Result? BAKING POWDERS 149 Wet the powder and paper. Remit? Into what ions would potassium hydrogen tartrate be dissociated by water? Equation ? What kind of ions produced the action on the litmus paper? Mix a little dry cream of tartar with a little dry baking soda, and pour the mixture into a dry test tube arranged with a one- hole stopper carrying a delivery tube that extends into some lime water in another test tube. Add a little water to the mixture of cream of tartar and baking soda, and immediately replace the stopper carrying the delivery tube. Result? Account for the fact that carbon dioxide is not evolved from a dry mixture of sodium bicarbonate and potassium acid tartrate, but is generated as soon as the mixture is wet. Complete the following equation, representing the reaction that takes place in the presence of water : NaHCOg + KH(C 4 H 4 6 ) >- NaK(C 4 H 4 O 6 ) + _ _+_ Cream of tartar baking powders consist of a mixture of cream of tartar, sodium bicarbonate, and some inert substance, such as starch or flour, which is used as a filler. Calculate the number of grams of sodium bicarbonate that would react with 10 grams of potassium acid tartrate. 150 LABORATORY EXERCISES Wliat volume of carbon dioxide, measured at standard conditions, would be evolved when the mixture was wet? What volume would the gas occupy at 21 C. and a pressure of 770 mm. ? One of the cream of tartar baking powders is prepared by mixing dry 2 parts by weight of cream of tartar, 1 part of sodium bicarbonate, and 1 part of starch. (c?) Phosphate powders. Sprinkle a few particles of monocalcium phosphate, CaH 4 (PO 4 ) 3 on a wet piece of blue litmus paper. Result? What ion derived from the monocalcium phosphate produces this change 9 Repeat the experiment, using monosodium phosphate, NaH 2 PO 4 , in place of monocalcium phosphate. Account for the reaction. BAKING POWDERS 151 Some phosphate baking powders consist of dry mixtures of monocalcium phosphate, sodium bicarbonate, and a filler ; other phosphate baking powders are dry mixtures of monosodium phosphate, sodium bicarbonate, and a filler. (c?) Alum baking powders. Sprinkle a few particles of sodium alum, sodium aluminum sulphate, NaAl(SO 4 ) 2 on a wet piece of blue litmus paper. Result? Sodium aluminum sulphate is a double salt, consisting of sodium sulphate in combination with aluminum sulphate. Alu- minum sulphate is hydrolyzed in solution (see 183, First Principles of Chemistry). Write an equation to shoiv this hydrolysis. Why does a water solution of alum give an acid reaction? Alum baking powders consist of dry mixtures of alum, sodium bicarbonate, and a filler. Why should a baking powder be stored in an air-tight container? Should a baking powder be mixed with the flour before or after the addition of water? Why? 152 LABORATORY EXERCISES EXPERIMENT 55 Preparation and Properties of Carbon Monoxide APPARATUS. Ring-stand with 1 ring and 1 clamp ; wire gauze with asbestos center; beaker, 200 cc. ; side arm test tube, with single hole rubber stopper to fit ; small thistle tube ; delivery tube ; en- ameled pan ; two wide- mouth bottles, 4 oz. ; glass plate ; bunsen burner. MATERIAL. Formic acid, sp. gr. 1.2; concentrated sulphuric acid; limewater. (a) Preparation. Arrange the apparatus as shown in Figure 47. Pour 5 cc. of formic acid and an equal amount of concentrated sulphu- ric acid through the thistle tube into the side arm test tube. Heat the water in the beaker until it boils. Collect the gas in small bottles as long as it is evolved. Do not let carbon monoxide escape into the room ; it is very poisonous. Figure 47. Get rid of the gas in any of the bottles that you do not need by burning it. (5) Properties. Burn a bottle of carbon monoxide. Describe the color of the flame. / . Compare this flame with that of burning hydrogen. Pour 15 cc. of limewater into the bottle in which the carbon monoxide has been burned and shake the liquid around gently. Result? & PREPARATION OF CARBON MONOXIDE 153 W/iat gas is formed by the burning of carbon monoxide f /, Write the equation for this reaction. (c) General questions., The formula of formic acid is HCHO 2 . Write the equation for its decomposition. + z 4- L6 + Explain how concentrated sulphuric acid helps to bring about this decomposition. (~A * / C/0 ^w/' 154 LABORATORY EXERCISES EXPERIMENT 56 Preparation and Properties of Carbon Monoxide Second Method APPARATUS. Flask, 250 cc.; two-hole rubber stopper to fit flask, pro- vided with thistle tube ; delivery and connecting tubes as shown in Figure 48; two wide-mouth bottles, 6 oz., provided with two-hole rubber stoppers and tubes as shown in the figure ; three wide- mouth bottles, 6 oz. ; pneumatic trough ; glass plate ; ring-stand with 1 ring and 1 clamp ; wire gauze with asbestos center ; bunsen burner ; two test tubes ; single hole rubber stopper to fit test tube, provided with L delivery tube. MATERIAL. Crystallized oxalic acid ; concentrated sulphuric acid ; caustic soda solution, 300 g. to the liter ; limewater. Caution ! Concentrated sulphuric acid, especially when hot, produces extremely serious burns ; also carbon monoxide is very poisonous. (#) Preliminary test. Put a pinch of oxalic acid in a test tube and add 1 cc. of concentrated sulphuric acid. Fit the test tube with a rubber stopper and delivery tube. Into a second test tube put 10 cc. of limewater. Heat the contents of the first tube gently, and allow the gas that is given off to pass through the limewater in the second tube. Result ? What gas is shown as one of the products of the action between oxalic and sulphuric acids ? (5) Preparation. Arrange the apparatus shown in Figure 48. Info the flask put 15 grams of oxalic acid. Into each of the two wide-mouth bottles put 30 cc. of caustic soda solution. Make sure that the tube by which the gas enters a bottle reaches nearly to the PROPERTIES OF CARBON MONOXIDE 155 bottom, and that the tube by which the gas leaves reaches only just below the rubber stopper. The thistle tube should reach nearly to the bottom of the flask. Pour about 20 or 30 cc. of sulphuric acid through the thistle tube into the flask. Heat the mixture with a small flame. When the action has started, remove the flame, but replace if the action becomes too slow. Collect in bottles in the pneumatic trough the gas that is given off. Compare the rates at which bubbles pass through the two wash bottles. Why are two bottles of caustic soda solution necessary 9 Figure 48. (tf) Properties. As soon as a bottle fills with the gas, remove it from the trough and hold its mouth to the flame. Why did the first bottles fail to ignite 9 Repeat the experiment, using a second bottle of the gas. Describe a carbon monoxide flame as to brightness and color. When you have burned a bottle of carbon monoxide, pour into it 20 cc. of limewater. Shake the limewater around in the bottle gently for a moment. Result 9 156 LABORATORY EXERCISES What is the product formed when carbon monoxide burns f Write the equation for the reaction.' (c?) General questions. What two gases result from the decomposition of oxalic acid by the aid of sulphuric acid ? From an inspection of the formula of oxalic acid, H 2 C 2 4 , decide what a third product is. Explain how sulphuric acid produces the action. Write the equation for the decomposition of oxalic acid. What happens in the 'wash bottles to the gas that was shown to be present in part (a) 9 Write an equation to show this. Why might the flames of hydrogen and of carbon monoxide be con- fused 9 How could you distinguish them by a test of the products of com- bustion 9 BORAX AND BORIC ACID 157 EXPERIMENT 57 Borax and Boric Acid ff* $ / D; 5 APPARATUS. Beaker, 100 cc. ; stirring rod; funnel; graduate, 50 cc. ; evaporating dish ; ring-stand with two rings ; wire gauze with asbes- tos center ; bunsen burner ; balance with weights ; pan of cold water ; test tube. MATERIAL. Filter paper; borax; sulphuric acid, concentrated ; alcohol; hydrochloric acid, 1 to 4 ; ammonia water, concentrated ; turmeric paper. (a) Preparation of boric acid. Weigh out, on a balanced filter, 12 grams of borax. Pour 50 cc. of water into a beaker and heat it to boiling on a wire gauze placed over a bunsen flame. Dissolve the borax in the hot water. Measure out 6 cc. of sulphuric acid and very slowly pour it down a stirring rod held just above the solution of borax, so that the acid will enter the solution drop by drop. Cool the solution by setting the beaker in a pan of cold | water. As the cooling proceeds, boric acid will crystallize out. Filter the mixture and wash the boric acid on the filter three or four times. Use a few cubic centimeters of cold water at a time and allow one portion of water to run through the filter before adding a second portion. What is the formula for the acid of which borax, Na^Oy, is a This acid combines with water to form boric acid, H 3 BO 3 . Taking these facts into consideration, write equations representing in two steps, the production of boric acid by the method you have employed. Then represent the reactions by a single equation. ////-/ Z A - 158 LABORATORY EXERCISES Account for the fact that the reaction runs in one direction (see Experiment 28). ^" ';/""" ...... ' Could hydrochloric acid be used in place of sulphuric acid? yC Why do you think so ? , What by-product was left in the liquid from which the boric acid crystallized ? Why were better results obtained by repeatedly washing the boric acid than could have been obtained by using the same quantity of ivash water at one time f (5) Alcohol test for boric acid. Place some of the boric acid you have prepared in an evapo- rating dish and just cover it with alcohol. Set fire to the alcohol. What color of the Jlame in addition to yellow do you observe f X ' ' C^"- . Treat a little borax in the same manner that you have just treated the boric acid. Hoiv does this Jlame differ in color from the preceding flame 9 (tf) Turmeric test for boric acid. Dip a piece of turmeric paper in a solution of boric acid and then dry the jfeper by wrapping it around a test tube containing boiling water. O/ // What change in the color of the turmeric do you observe ? Add to the paper a little ammonium hydroxide. What change in color do you observe ? BORAX AND BORIC ACID 159 Determine whether dilute hydrochloric acid will restore the color of turmeric paper after it has been changed by boric acid and ammonium hydroxide. Besult? i ttt44L >^ Test for borax. Acidulate a solution of borax with hydrochloric acid and make the turmeric paper test for boric acid. 160 LABORATORY EXERCISES EXPERIMENT 58" Water Softening APPARATUS. Dropping bottle with notched cork; funnel; four test tubes ; bunsen burner. MATERIAL. Calcium sulphate (plaster of Paris) ; magnesium sulphate ; temporary hard water ; limewater ; sodium carbonate solution ; fil- tered soap solution ; filter paper. (&) Boil one third of a test tube of temporary hard water. Result? / */ $ y ?>/ How does the boiling soften the water? t/ufrbi ffe-, & Complete the equation : CaH 2 (C0 8 ) 2 -_ . + . _ + . What becomes of the substance, that causes the hardness ? Temporary hard waters, before being fed to boilers, are some- times brought to boiling in a feed water Beater. Why ? Why is the water then filtered before passing it into the boiler where steam is generated f (6) To one third of a test tube of temporary hard water add an equal volume of limewater. Result ? Write the equation for the action of limewater on the temporary hard water. WATER SOFTENING 161 What acid must be in excess when calcium bicarbonate is formed ? Write the equation for the neutralization of this acid with lime- water. Which product is the precipitate f How is limewater made ? Why is lime added to tanks of temporary hard water in a water- softening plant ? (c) Prepare a permanent hard water by shaking a pinch of calcium sulphate (plaster of Paris) in a test tube of water and then filtering the liquid. Pour half of this hard water into another test tube and set it aside for later use. To the other half of the hard water, slowly add a sodium car- bonate solution from a dropping bottle, as long as any precipi- tate forms. Shake the tube after each addition of the carbonate. Write the equation for the reaction. Which of the two products do you know to be an insoluble substance ? Remove the precipitate from the liquid by filtering. Test the filtrate with soap solution to determine the readiness with which it forms permanent suds. ResuU f Similarly try the soap solution with the portion of the orig- inal hard water that was set aside. Which forms suds more readily, the original hard water, or the water to which sodium carbonate was added ? 162 LABORATORY EXERCISES Take half a test tube of temporary hard water and add to it a pinch of calcium sulphate and a pinch of magnesium sulphate. Add water to fill the test tube and mix the contents by shaking. If the liquid is not clear, filter it. This repre- sents a common type of hard water that contains several causes of hardness. To the hard water add limewater, a few drops at a time, as long as a precipitate forms. Filter the liquid. To the filtrate add sodium carbonate solution from the dropping bottle as long as precipitation occurs. Filter the liquid and test the filtrate with soap solution. Result ? Was the hardness due to magnesium removed from the water by the lime and soda treatment (i.e. limewater and sodium carbonate)? BLEACHING OF COTTON 163 (cV * EXPERIMENT 59 Bleaching of Cotton APPARATUS. Porcelain mortar and pestle; 1000 cc. graduate; two beakers, 250 cc. ; glass stirring rods; ring-stand with ring; wire gauze with asbestos center ; burisen burner. MATERIAL. Unbleached cotton waste ; litmus paper ; solutions prepared as directed below ; bleaching powder ; sodium hydroxide ; sodium thiosulphate ; concentrated sulphuric acid ; starch ; sodium iodide. Preparation of Solutions. The quantities given are sufficient for a class of ten pupils. Alkali. Dissolve 16 g. of sodium hydroxide in 1000 cc. of water. Bleaching Solution. Work 10 g. of a good quality of bleaching powder into a smooth, thin paste with a little water in a porcelain mortar. Rinse the paste into a 1000 cc. graduate, and then add water until the graduate is filled to the 800 cc. mark. Pour the mixture into a bottle, shake it thor- oughly, and then allow the undissolved matter to settle. Use only the clear supernatant liquid. Acid. Pour 30 cc. of concentrated sulphuric acid into 500 cc. of water. Antichlor. Dissolve 2 g. of sodium thiosulphate ("hypo") in 500 cc. of water. Starch Iodide Paste. Mix some starch with cold water and. slowly pour the mixture into 50 cc. of boiling water. Stir constantly and discontinue the addition of starch and the boiling as soon as a thin paste has been ob- tained. Add 5 cc. of a dilute solution of sodium iodide to the starch paste and mix the two thoroughly by stirring. (a) Cotton yarn and cloth are " boiled out " to remove wax, grease, and dirt which would prevent the uniform action of the bleach on the fibre. Pour 100 cc. of the alkali solution into a 200 cc. beaker and immerse in the liquid about a gram of cotton waste. Heat the liquid to boiling, and continue to boil it gently for 10 minutes, meanwhile keep the cotton in motion in the liquid by means of a stirring rod. What evidence is there that substances have been removed from the cotton f Remove the waste and rinse it repeatedly in water. 164 LABORATORY EXERCISES (6) Pour 50 cc. of the bleaching solution into a beaker and put the wet cotton waste into it. By means of a glass rod, work the cotton in the liquid for at least five minutes and then allow it to remain in the liquid another five minutes. (- + + \, Chlorine reacts with water to produce hydrochloric acid and oxygen, which changes the coloring matter of many colored compounds into a colorless substance. (cT) Use of antichlor. Free chlorine must not be permitted to remain in contact with the cotton fiber, because chlorine weakens the strength of the fiber by reacting with it. Wash the cotton to remove the acid. How can you determine when this has been accomplished f Put a little of the starch iodide paste on the cotton. Look carefully to see whether a blue tint is developed. Chlorine liberates iodine from sodium iodide, and iodine reacts with starch to yield a blue substance. Complete the equation : C1 2 + Nal - + ' BLEACHING OF COTTON 165 Soak the cotton waste in 50 cc. of the antichlor, rinse the cotton thoroughly, and again use the starch iodide paste to test for chlorine. Balance the equation : Na 2 S 2 O 3 + H 2 O 4- C1 2 > H 2 S0 4 + HC1 + 166 LABORATORY EXERCISES EXPERIMENT 60 Four Ways of Preparing a Salt, Sodium Chloride These methods are placed together for convenience. The exercise should be assigned in advance, and the calculations in part (c) should be made before coming to the laboratory. APPARATUS. Apparatus for making chlorine, 1 set for each group of five pupils. Apparatus similar to that shown in Figure 18 is conven- ient, and consists of a 250 cc. flask with 2-hole stopper carrying a thistle tube and a delivery tube arranged for use in the collection of a gas by the downward displacement of air, a ring-stand with 1 ring, a clamp, a small pan of water, and a bunsen burner. Bottle, 8 oz. ; cover glass ; ring- stand with one ring ; bunsen burner ; bottle with notched stopper for dropping hydrochloric acid ; two test tubes ; funnel ; evaporating dish ; stirring rod ; deflagration spoon ; gradu- ate, 100 cc. ; wire gauze with asbestos center. MATERIAL. Fine sand ; sodium ; manganese dioxide ; hydrochloric acid, concentrated ; hydrochloric acid, 1 to 4 ; sodium hydroxide solution, 1 to 10; solution of crystallized barium chloride, 104 grams of BaCl 2 2 H 2 O per liter ; solution of crystallized sodium sulphate, 137.5 grams of Na 2 SO 4 10H 2 per liter; sodium car- bonate, dry; litmus paper, red and blue. (a) Direct combination. This part of the experiment should be performed under a hood. Collect an 8 oz. bottle of chlorine prepared by any conven- ient method, for example that described in Experiment 18. Half fill the bowl of a deflagration spoon with sand. Ask the instructor to place a piece of clean sodium on the sand. At once take the sodium to the hood containing the bottle of chlorine, ignite the sodium by directing a flame against it, and immediately lower the burning sodium into the chlorine. What chemical reaction takes place between the sodium and the chlorine? , , FOUR WATS OF PREPARING A SALT 167 Why did it occur readily (see Experiment $6) ? . ^ By what properties canj/ou identify the^ product? ^^^^^^t> Name the product. (5) Neutralization. In a porcelain evaporating dish, neutralize 5 cc. of a solution of sodium hydroxide with a solution of dilute hydrochloric acid. Evaporate the neutral solution to dryness. What is the name of the solid obtained ? -fy^^/r ^L^cL What ion does every water solution of an acid contain? ^b/ft A^i/ V' What ion does every water solution of a base contain? j&f /T What becomes of these ions during the process of neutralization? t/J n j-t|Af n if A j jff~ u - Why does the reaction go to an end ? Be. SO ^ri *** - 168 LABORATORY EXERCISES Using the equation Na 2 S0 4 10 H 2 + BaCl 2 2 H 2 -> BaS0 4 + 2 NaCl + 12 H 2 0, and the table of atomic weights on page 234) calculate (a) the number of grams of crystallized sodium sulphate. (6) the number of grams of crystallized barium chloride, required to prepare 1 gram of sodium chloride. The stock solution of barium chloride contains 104 grams of crystallized barium chloride per liter. The stock solution of sodium sulphate contains 137.5 grams of crystallized sodium sulphate per liter. Calculate the number of cubic centimeters of (#) the stock solu- tion of barium chloride, (6) the stock solution of sodium sulphate, containing the weights of barium chloride and sodium sulphate respectively that you found would react to yield 1 gram of sodium chloride. FOUR WAYS OF PREPARING A SALT 169 Why are these calculations necessary 9 Measure out the volume of barium chloride solution re- quired and pour it into a test tube. Measure out the volume of sodium sulphate required. Pour the sodium sulphate solu- tion into an evaporating dish, heat the solution, and add the barium chloride solution to it. Allow the mixture to stand for a few minutes and then filter it, using a good quality of filter paper. If the first portion of the filtrate is not clear, repeat the operation. What is the precipitate 9 What salt is contained in the filtrate? Obtain the salt from the filtrate. How did you accomplish the separation of the two compounds produced 9 ' fa 6 MM, 'far? Double replacement due to the volatility of one of the products. Add slowly, with constant stirring, hydrochloric acid, 1 to 4, to about 2 grams of sodium carbonate, until all of the sodium carbonate has dissolved. What gas is generated 9 Account for its production. <*Jt C^ ***M *^+%Z* ^tdffl, b&'X&f* Why did the reaction go to an end 9 Evaporate the solution to dryness. What became of the excess of hydrochloric acid? &r 4* Why did the reaction go to an end 9 \J^4<7 170 LABORATORY EXERCISES EXPERIMENT 61 Cobalt Nitrate Tests APPARATUS. Plaster block, made by pouring a thin mixture of plaster of Paris and water into a form on a glass or stone slab and cutting the mass just before it hardens into strips of suitable size ; blowpipe ; forceps ; bunsen burner. MATERIAL. Zinc sulphate ; alum ; magnesium sulphate ; cobalt nitrate solution in bottle provided with dropper ; unknowns. (#) Put a little of some zinc compound, as zinc sulphate, in a cavity made in a plaster block with the top of a pair of forceps. Heat it as hot as possible at the end of a small blow- pipe flame. Allow the residue to cool. Record the color of the residue in a. table like that on page 171. Moisten the residue with a drop or two of cobalt nitrate solution. Again heat it intensely, and, on cooling, note the color of the mass that remains on the plaster block. Record in the table the color obtained. (5) Place an aluminum compound, as alum, in a fresh cavity in the block. Repeat the test made with the zinc co'mpound, so as to obtain a characteristic coloration. Record the results in the table. ( 5 TESTS FOR IRON SALTS 183 To a mixture of solutions of ferrous sulphate and ferric chloride add a few drops of potassium ferrocyanide solution. Which color obscures the other? Q i. ^5L * 7s potassium ferrocyanide a test for the ferrous or for the ferric (6) To 5 cc. of a solution of ferrous sulphate (or other ferrous salt), add a few drops of potassium ferricyanide. Record the color of the precipitate in the table. &,&&&&*& < This is known as Turnbull's blue. Write the equation for its formation. r' ^Lj// PA ( (li*) *-V" / J r>o uq UK-S rO~ L ^v / ' ^. To 5 cc. of a solution of ferric chloride (or other ferric salt), add a few drops of potassium ferricyanide. Fill the test tube with water, shake the contents, and examine the mixture closely, to see whether the liquid is clear or a precipitate is formed. Record the result in the table. To a mixture of solutions of ferrous sulphate and ferric chloride, add a few drops of potassium ferricyanide. Is the precipitate due to the ferrous or to the ferric salt? Is potassium ferricyanide a test for the ferrous or for the ferric- ion? TABLE IRON SALTS POTASSIUM FEKROCYANIDE, Kotassium alum from 2)otassium sulphate and aluminum sulphate. Weigh out 15 grams of crystallized aluminum sulphate, A1 2 (S0 4 ) 3 .18H 2 0. Calculate from the equation how many grams of potassium sul- phate are needed. Weigh out the calculated amount of potassium sulphate and dissolve in 40 cc. of hot water. In another beaker dissolve the aluminum sulphate in 40 cc. of hot water. Mix the two solutions and set the mixture aside to crystal- lize in a place where the beaker will not be disturbed. 206 LABORATORY EXERCISES 0) Ammonium alum, (NH 4 )Al(SO 4 ) a 12 H 2 O. MATERIAL. Crystallized aluminum sulphate ; ammonium hydroxide, sp. gr. 0.90 ; sulphuric acid, 1:10; filter paper ; red and blue litmus papers. Weigh out 15 grams of aluminum sulphate, and dissolve it in 40 cc. of water. Add 4.5 cc. of ammonium hydroxide solution to 15 cc. of water, neutralize it with dilute sulphuric acid, and then dilute it to about 40 cc. Mix the two solutions, filter the mixture if it is not clear, and evaporate the solution to half the bulk. Set the solution aside to crystallize. Describe the color and general form of the crystals. Write the equations for the reactions taking place. Ferric ammonium alum, (NH 4 )Fe(SO 4 ) 2 12 H 2 O. MATERIAL. Filter paper ; ammonium hydroxide, iron wire or nails ; sulphuric acid, 1:10; concentrated nitric acid ; red and blue litmus papers. Prepare a solution of ferrous sulphate as in part (a). Prepare a solution of ammonium sulphate as in part (a). To the filtered solution of ferrous sulphate in a beaker, add 25 cc. of the sulphuric acid, and 1 cc. of concentrated nitric acid. Boil as long as nitric oxide is evolved. Into what gas is nitric oxide converted on coming in contact with air? The iron is now in solution as ferric sulphate, Fe 2 (SO 4 ) 3 . Write the equation for the reaction. DOUBLE SALTS 207 Add the solution of ammonium sulphate to the solution of ferric sulphate, evaporate until the bulk is reduced to one half. Set the beaker aside to cool slowly until the contents crystallize. Describe the color and general form of the crystals. The crystals may be dried between blotters ; they must be preserved in well-stoppered bottles. Write the equation for the reaction between the sulphate of iron and the ammonium sulphate. () Rochelle salt, NaK(C 4 H 4 O 6 ) - 4 H 2 O. MATERIAL. Cream of tartar ; bicarbonate of soda ; fitter paper. Weigh out 14 g. of acid potassium tartrate (cream of tartar), KH(C 4 H 4 O 6 ). Mix it with 15 cc. of water. Does it completely dissolve in this quantity of water? Weigh out 6 g. of sodium bicarbonate, NaHCO 3 , and mix it with 15 cc. of water. Does it completely dissolve in this quantity of water? While stirring, slowly pour the sodium bicarbonate solution into that of the tartrate, and pour back from beaker to beaker until action ceases. What gas is evolved ? Is all the solid dissolved ? 208 LABORATOBY EXERCISES If the liquid is not clear, filter it, and evaporate it to half bulk and set it aside to crystallize. Better crystals may be obtained by setting it aside to evaporate without heating, but do not let it evaporate to dryness. Pour off the mother liquor and dry the crystals between blotters or filter paper. Write the equation for the reaction between sodium bicarbonate and cream of tartar. (/) Rochelle salt, NaK(C 4 H 4 O 6 ) . 4 H 2 O. ATERIAL. Tartaric acid ; sodium hyd droxide, 1 : 10; phenolphthalein paper. MATERIAL. Tartaric acid ; sodium hydroxide, 1 : 10; potassium hy- Dissolve 5 g. of tartaric acid in 10 cc. of water. Exactly / neutralize it with sodium hydroxide. Dissolve 5 g. of tartaric acid in 10 cc. of water. Exactly ;'/ neutralize it with potassium hydroxide. Mix the two solutions and evaporate to one half the bulk or, to get good crystals, set it aside to evaporate slowly to one fourth the bulk. Pour off the mother liquor and dry the crystals between blotters or filter paper. Write the equation for the reaction between sodium hydroxide and tartaric acid, H 2 (C 4 H 4 6 ). Write the equation for the reaction between potassium hydroxide and tartaric acid. Write the equation for the reaction which resulted in the formation of the Rochelle salt. DOUBLE SALTS 209 ($r) Ammonium sodium tartrate. MATERIAL. Tartaric acid ; ammonium hydroxide ; sodium hydroxide; phenolphthalein paper. Proceed as above, but use ammonium hydroxide instead of potassium hydroxide. Ammonium sodium tartrate does not crystallize as well as Rochelle salt. Write equation as in part (/). 210 LABORATORY EXERCISES (^ "V , \ Ot~ EXPERIMENT 76 Qualitative Separation of Lead, Silver, and Mercury APPARATUS. Test tubes ; test tube rack ; funnel ; bunsen burner. MATERIAL. Hydrochloric acid concentrated and dilute ; nitric acid concentrated and dilute ; ammonium hydroxide 1 to 3 ; solutions of lead, silver, and mercurous nitrates ; potassium chromate solution ; copper strip ; filter paper ; unknown solutions. (a) In one test tube take 10 cc. of a solution of lead nitrate ; and in another, 10 cc. of a solution of silver nitrate. To both test tubes add dilute hydrochloric acid till the reaction is com- plete. , , , / * > \ Results? ,. -i , Write the equations. ( 4 "it : ^ ' i Allow the precipitates to settle and then pour off the super- natant liquid from each of the two test tubes. Add to the precipitates in the test tubes enough cold water to nearly fill the tubes, and shake the contents. Again let the precipitates settle and then pour off the supernatant liquids. What compound has been removed by washing the precipitate and then pouring off the supernatant liquid ? Try the effect of hot water on the precipitate of lead chloride. Result? Divide the precipitate of silver chloride between two test tubes. With one part try the effect of hot water ; with the other, the effect of ammonium hydroxide. SEPARATION OF LEAD, SILVER, AND MERCURY 211 Results? - M.HL,.&'-&-4& ti^U~i*** Cxt^**W *^~ A 212 LABORATORY EXERCISES Give name, formula, and color of the characteristic compound formed. Wash the precipitate remaining on the filter paper with ammonium hydroxide, keeping the washings. Which chloride gives the color? What chloride is contained in the ammonium hydroxide filtrate ? Prove the presence of this chloride by adding a slight excess of nitric acid. Name the precipitate and state the characteristic properties by which you recognize it. To dissolve the precipitate still remaining on the filter paper, add a little aqua regia (9 drops concentrated hydrochloric acid to 3 drops concentrated nitric acid). Dilute with water the solution thus obtained, and put into it a bright strip of copper. After several minutes, remove the strip, and wash and rub it. Result? Explain why this dissolving in aqua regia and the addition of a copper strip is a confirmatory test. (c?) Obtain from the instructor an unknown solution. Using" the methods in (V), analyze the solution for lead, silver, and mercury. SEPARATION OF LEAD, SILVER, AND MERCURY 213 Record all the steps, even those giving negative results. Underline the metal found in your unknoivn. lead mercury silver 214 LABORATORY EXERCISES EXPERIMENT 77 Chromium Compounds APPARATUS. Two beakers, 250 cc. ; two test tubes; graduate; balance and weights ; bunsen burner. MATERIAL. Potassium dichromate ; potassium hydroxide ; sodium peroxide ; chromium sulphate or chrome alum ; alcohol ; dilute nitric acid ; concentrated sulphuric acid. (a) Pulverize 10 grams of potassium dichromate and dissolve it in 50 cc. of water. The color of the solution is characteristic of dichromate ions. (5) Dissolve 10 grams of potassium hydroxide in 100 cc. of water. ((?) Slowly add, with constant stirring, the solution prepared in (>) to that prepared in (#) until the resulting liquid is of a pure yellow color. The color is characteristic of chromate ions. Complete the equation :/ K 2 Cr 2 7 + 2 KOH V 1-^ 2 K 2 CrO 4 + _ Any strong base would produce this change. K O Cr The structural formula for potassium dichromate is \0 K O Cr^zO %0 K - The structural formula for potassium chromate is What is the valence of chromium in each case ? (cT) Add a dilute solution of nitric acid to the solution ob- tained in (\ 4 When a dichromate is changed into a chromic salt, is the change one of oxidation or of reduction ? rt / Why? (/) Add sodium peroxide, a little at a time, to 1 gram of chromium sulphate or chrome alum dissolved in 25 cc. of water, until the yellow color characteristic of chromate ions has been produced. What element is liberated when sodium peroxide is added to water? What base is formed ? change takes place when a chromic salt is oxidized in the presence of a base? 216 LABORATORY EXERCISES P V ' EXPERIMENT 78 Fermentation APPARATUS. Acid bottle, capacity about 2^ liters ; two wide-mouth bottles, capacity about 500 cc. ; stoppers and tubes shown in Figure 54 test tube; boiling flask, 250 cc. ; U-tube, 6" ; battery jar, 5" high stoppers and tubes shown in Figure 55 ; thermometer ; watch glass beaker, 100 cc. ; ring-stand with 1 ring and a small clamp; bunsen burner ; wire gauze with asbestos center. MATERIAL. Molasses; two yeast cakes; limewater ; iodine; quick- lime ; sodium hydroxide solution ; candle or splinter. (a) Fermentation. Arrange apparatus as shown in Figure 54. One set of ap- paratus will furnish sufficient fermented liquid for ten pupils to use in part (6). Pour 1 vol- =M=^ ume O f m olasses dissolved in 4m 6 volumes of water into the acid bottle. Break two yeast cakes into small fragments and stir them into a little luke- warm water, so as to form a thin paste. Pour the paste into the bottle containing the solution of molasses, then shake the bottle so as to distribute the yeast through the molasses. y Figure 54. After replacing the stopper in the acid bottle, remove the stopper from the wide-mouth bottle connected with the acid bottle, and fill the bottle with water. Replace the stopper. Some of the water will be forced into the third bottle, but no siphoning can take place since air cannot enter the acid bottle. Allow the apparatus and contents to remain in a warm place for several days (about a week). From time to time, examine the contents of the bottles. FERMENTATION 217 What change do you notice in the color of the liquid in the acid tip. 9 bottle? What has happened to the water in the wide-mouth bottles?. While the action is in progress, remove the third bottle for a moment and replace it with a test tube containing a little lime- water so arranged that the end of the delivery tube will be in the limewater. Account for the result. After the action has been going on for several days, remove the stopper from the bottle filled with gas and lower into it a lighted candle, or burning splinter. Results? What is the name of the gas? (5) Fractional distillation. Arrange apparatus as shown in Figure 55. Siphon off enough of the fer- mented liquid to half fill a dis- tilling flask and clamp the flask in place. Insert the thermome- ter so that its bulb is in the neck of the flask just below the de- livery tube. Figure 55. 218 LABORATORY EXERCISES After connecting the condensing tube to the flask, bring the liquid in the flask to a gentle boil, then regulate the tempera- ture very carefully, in order to prevent froth from being formed and passing over into the distillation tube. Why should the water in the battery jar be changed occasionally or lumps of ice be put in the water ? At ivhat temperature does the liquid commence to distil over? When the temperature has reached 85, take away the flame. Remove the U-tube from the water, wipe it dry on the outside, and pour enough of its contents into a watch glass to make a circle as big as a quarter. Hold a bunsen flame to the watch glass for a moment. What happens? What is shown to be present by this test? After the action is over, is any liquid left in the watch glass? Stop the distillation at 99 C. At the close of the distillation try to ignite a few drops of the distillate. Result? Throw away the liquid in the flask. Place in the distilling flask a number of small lumps of quicklime. Pour the first distillate back into the flask and redistil it, noticing the temperature of the vapor. Why is the lime used ? Identify the second distillate (a) by its odor, (5) by bringing a lighted match to a small portion in a watch glass, and ( Organic fats and oils are esters of the alcohol glycerine and fatty acids. How are such fats and oils converted into soap? What alcohol is a by-product of soap making f What became of it in the case of the soap just made? STARCH 223 V2 x: *t 1 EXPERIMENT 81 Starch APPARATUS. Beaker, 150 cc. ; three test tubes; glass stirring rod; funnel ; porcelain evaporating dish ; sand bath ; ring-stand with large and small rings ; wire gauze with asbestos center ; bunsen burner. MATERIAL. Starch ; potassium iodide solution of iodine ; glucose ; Fehling solution ; hydrochloric acid. (a) Starch heated with water. To one sixth of a test tube of water add a pinch of starch and shake the tube. Does the uncooked starch dissolve 9 Boil the mixture in the test tube until a gelatinous mass has been formed. Pour the mass into a beaker of water and stir thoroughly. Does the boiled starch dissolve? When starch is heated with water, the cellulose envelope inclosing each starch granule bursts, and a gelatinous mass is formed. On longer heating some of the starch passes into solution. Half fill a test tube from the beaker containing the starch solu- tion and keep the test tube for part (6) Test for starch. Add a drop of iodine solution to the contents of the beaker. Result? 224 LABORATORY EXERCISES (c) Conversion to dextrine . Support an evaporating dish in the small ring of a ring-stand. Place one third of a test-tubeful of starch in the dish, having it well above the small flame of abunsen burner (Figure 56). The starch should be heated just hot enough to turn it barely yellow, but not hot enough to char it. The temperature of conversion from starch to dextrine is be- tween 200 and 250 C. Continue the heating for fifteen minutes, stirring meanwhile with a glass rod ; then allow the dish to cool. Add a little water ^^ ^^^ to the mass in the dish, and stir the mixture. Rub some of the mass between the fingers. What characteristic has it? Figure 56. This is due to the fact that some of the starch has been con- verted into dextrine. Why is dextrine used in making mucilage and other adhesives? Pour a few drops of the liquid in the evaporating dish into a test tube two thirds filled with water, and shake the test tube. Then add a drop of iodine solution. The violet to red color produced is characteristic of dextrine. Test for glucose. Dissolve a little glucose in 10 cc. of water. Heat in a second test tube 10 cc. of Fehling's solution to the boiling point. To this hot liquid add a little of the glucose solution. Result? STARCH 225 To some of the starch solution kept from part (a), add 10 cc. of the hot Fehling's solution. Result? (e) Conversion of starch to glucose. Put a little starch into a third of a test tube of water and then add three or four drops of hydrochloric acid. Boil the mixture for ten minutes. Test the resulting liquid with Fehling's solution. Result? What change has occurred? 226 LABORATORY EXERCISES EXPERIMENT 82 Food Constituents. Part I Fats. Protein APPARATUS. Test tubes ; bunsen burner ; ring- stand with one large and one very small ring ; two porcelain evaporating dishes ; beaker, 150 cc. MATERIAL. Benzol ; filter paper ; Geis's biuret reagent, made by add- ing 3 per cent copper sulphate solution to 10 per cent potassium hydroxide solution a drop at a time, until a faint but perceptible blue color is imparted to the resulting solution ; foods for testing, such as fat meat, flour, milk, nuts, sugar, peas, etc. Test several foods as directed below, and fill in the tabular form. (a) Test for oil or fat. Divide as finely as possible the sample to be tested. Use enough to fill a test tube to the depth of one half to three fourths of an inch. Add benzol to cover the solid to the depth of one half inch. Caution ! Benzol is inflammable. Warm the contents gently by standing the test tube in a beaker of hot water. Allow the test tube to stand for five minutes, with occasional shaking and warming. Fold a filter paper as for a funnel. Suspend it in a small ring in the ring-stand. Pour a few drops of the liquid from the test tube into the point of the filter paper, and allow the benzol to evaporate completely. If the food contains oil or fat, more or less of a line of grease will be left around the stained spot on the paper. This can be more easily seen if the paper is held to the light ; the grease spot then appears lighter than the rest of the paper. Why was benzol used? FATS. PBOTEIN 227 Why was the sample of food divided as finely as possible? (b) Test for protein. Use the food either as a solution or in as finely divided state as possible. Put it into an evaporating dish, and add 5 cc. of Geis's biuret reagent. Put the same quantity of the reagent into a second evaporating dish for comparison in detecting a change of color. If the food contains protein matter, the solu- tion in the first dish will acquire a pink or violet color. The change will be readily seen if the two dishes are compared. Test several foods and record your results in the table. Which of the foods contained no protein ? TABLE FOOD TESTED FAT PRESENT OR ABSENT ? PROTEIN PRESENT OR ABSENT ? 228 LABORATORY EXERCISES EXPERIMENT 83 Food Constituents. Part II Carbohydrates APPARATUS. Test tubes ; bunsen burner. MATERIAL. Starch ; glucose ; cane sugar ; fruit ; potato ; flour ; meat ; beets ; potassium iodide solution of iodine ; Fehling's solution (pur- chase as two solutions and mix just before using) ; hydrochloric acid Molisch's reagent (15 per cent solution of a-naphthol in alcohol); concentrated sulphuric acid. (a) Test for carbohydrates. (Molischtest.) To 5 cc. of a solution obtained by boiling the ground food with water for several minutes, add 2 drops of a solution of a- naphthol (15 per cent solution in alcohol). Hold the tube con- taining this mixture in an inclined position, and add slowly 3 cc. of concentrated sulphuric acid in such a manner that it slides down the side of the tube and makes a separate layer below the mixture already present in the tube. A purple ring will form between the two layers if the original solution con- tained any carbohydrate. Result? (5) Test for starch. To a pinch of starch add 5 cc. of water and boil the mixture in a test tube till a gelatinous mass has been formed. Dilute this by nearly filling the tube with water. Add a drop of iodine solution. Result? CARBOHYDRATES 229 (c) Test for glucose. Dissolve a little glucose in 10 cc. of water. Heat in a second test tube 10 cc. of Fehling's solution to the boiling point. To this hot liquid add a little of the solution of glucose. Result? (c?) Formation of glucose from starch and cane sugar. To about 1 gram of the starch add 10 ec. of water and 3 or 4 drops of hydrochloric acid. Boil the mixture for ten minutes. Test the resulting solution for glucose. In a similar way, boil cane sugar solution with hydrochloric acid and test the product for glucose. Result? Under what circumstances can Fehling's solution be used as a test for cane sugar? (e) Test of samples. Test the samples of food given you, first for carbohydrates in general, and then for starch and glucose. If a food contains neither of these, test it for cane sugar. Use the food in a finely divided state, and boil about 1 gram of it with 10 cc. of water for five minutes before making the test. Record your results in the table on page 230. Why can not the test for cane sugar be used in the presence of starch? 230 LABORATORY EXERCISES TABLE FOOD TESTED STARCH PRESENT OB ABSENT ? GLUCOSE (OR CANE SUGAR) PRESENT OR ABSENT? CONSTITUENTS OF MILK 231 EXPERIMENT 84 Constituents of Milk APPARATUS. Graduate, 100 cc. ; beakers, 100 cc., 250 cc., 500 cc. ; watch glass to cover 250 cc. beaker ; funnel ; glass stirring rod ; porcelain crucible, # ; pipe-stem triangle ; wire gauze with asbestos center ; ring- stand with two rings ; bunsen burner ; test tube ; two evaporating dishes. MATERIAL. Sample of sweet milk;, acetic acid, 10 cc. glacial acetic acid in 740 cc. of water ; sodium hydroxide solution, 4 grams of NaOH per liter ; piece of blotting paper a little smaller in diameter than the watch glass ; filter paper to fit funnel ; carbon tetrachloride ; Geis's biuret reagent ; Fehling's solution ; milk sugar ; distilled water. (0) Casein. Pour 25 cc. of milk into a 500 cc. beaker and add 175 cc. of distilled water. Now add, a drop at a time with constant stirring, 40 cc. of the solution of acetic acid. Allow the mixture to stand for about 20 minutes, meanwhile proceeding with part (6). Then filter the milk. Save the filtrate for use in part (c). Why does milk curdle when it enters the stomach? Put the paper and contents into a beaker of water and rinse the precipitate from the paper. The precipitate is casein. Test this for protein by the method given in Experiment 82. Result? Allow the casein to settle, then pour off the liquid and add to the casein 100 cc. of the sodium hydroxide solution. If the casein does not dissolve, add a little more of the alkali. How could casein be reprecipitated from this solution? 232 LABORATORY EXERCISES (6) Fat. Half fill a 250 cc. beaker with water. Set it on a piece of wire gauze placed on the ring of a ring-stand, and heat the water. As soon as the water commences to boil, lower the flame so it will furnish only enough heat to keep the water boiling gently. While waiting for the water to boil, wet the piece of blotting paper with milk by pouring a thoroughly mixed sample down a stirring rod so that it will drop on the paper in such a manner as to distribute the milk evenly over the surface of the paper. Put the paper wet with milk 011 the watch glass, set the glass on the beaker of boiling water, and allow it to remain until the milk has evaporated to dryness. Remove the watch glass containing the paper and allow it to cool. When the glass is cold, pour into it sufficient carbon tetrachloride to cover the paper. Work the paper in the liquid by means of a stirring rod for two or three minutes, then remove the paper arid evaporate the carbon tetrachloride over steam. What remains on the ivatch glass ? (c) Lactalbumen. Heat the nitrate obtained in part (a) to boiling and continue the boiling until a clear fluid can be obtained by filtration. Save this filtrate for use in part (cT). The residue is lactal- bumen. Determine whether it is a protein. Result? Casein does not coagulate when milk is boiled. What is the scum that appears on the surface of boiling milk? Sugar. Fill one third of a test tube with the filtrate obtained in part ), add sufficient Fehling's solution to have the tube half full CONSTITUENTS OF MILK 233 of the mixture, and heat the contents of the tube to boiling. Lactose, milk sugar, reduces Fehling's solution in a manner similar to glucose. See Experiment 83. Examine a sample of milk sugar. How does its siveetness compare with that of sugar? (e) Ash. Evaporate 5 cc. of milk to dryriess in a porcelain crucible placed on a pipe-stem triangle supported on the rim of a beaker containing boiling water. Dry the crucible, then gradually raise the temperature to the full capacity of your bunsen burner. Continue the heat until the carbon has been completely burned and only a white ash remains. Would milk sugar leave an ash ? APPENDIX APPENDIX I. PHYSICAL CONSTANTS OF THE IMPORTANT ELEMENTS Approximate Weights Should Be Used in All Calculations, Except Those of Equivalents ELEMENT SYMBOL ATOMIC WEIGHTS VALENCE SPECIFIC GRAVITY MELTING POINT BOIUNO POINT Approx- imate Exact O=16 Water =1 Air = 1 C. C. Aluminum Al 27 27.1 III 2.7 657 2200 Antimony Sb 120 120.2 III V 6.6 630 1600 Argon A 40 39.88 1.38 - 188 -186 Arsenic As 75 74.96 III V 5.7 . . . <449 sublimes Barium Ba 137 137.37 II 3.8 850 950 Bismuth Bi 208 208.0 III V 9.7 269 1435 Boron B 11 11.0 III 2.4 infusible 3500 sublimes Bromine Br 80 79.92 I 3.1 -7.3 59 Cadmium Cd 112 112.4 II 8.6 321 778 about Calcium Ca 40 40.07 II 1.5 805 . . . amorphous Carbon C 12 12.005 IV 1.7-2.1 infusible 3500 Chlorine Cl 35.5 35.46 I 2.49 - 102 -33.6 Chromium Cr 52 52.0 II III VI 6.9 1505 2200 Cobalt Co 59 58.97 II 8.7 1490 . Copper Cu 63.6 63.57 III 8.9 1083 2310 Fluorine F 19 19.0 I 1.31 -223 - 187 Gold An 197 197.2 I III 19.3 1062 2630 Helium, He 4 4 00 14 960 9fifi ^ Hydrogen H 1 3.008 I U. IT: 0.07 -^ \ju -259 ^Oo. O -252 Iodine I 127 126 92 I 4.9 114 184 Iron Fe 56 55.84 II III 7.9 1530 2450 Lead Pb 207 207.2 II IV 11.3 327 1525 234 PHYSICAL CONSTANTS 235 Kl.EMF.NT SYMBOL ATOMIC WEIGHTS VALENCE SPECIFIC GRAVITY MELTING POINT BOILING POINT Approx- imate Exact O 16 Water ~1 Air = 1 <\ 0. Lithium Li 7 6.94 I 0.03 186 <1400 Magnesium M.u 24 24.32 II 1.7 650 1120 Manganese 1 Mn 55 54.93 II IV 7.4 1225 1900 Mercury Hg 200 200.6 I II 13 6 -38.8 357 > Nickel Ni 58.7 58.68 II 8.7 1450 ( Nitrogen N 14 14.01 IIIV 0.97 -213 -195 Oxygen O 16 16.00 II 1.10 <-227 -183 white wh ite Phosphorus P 31 31.04 IIIV 1.8 44.1 290 Platinum Pt 195 195.2 IV 21.2 1753 . . . Potassium K 39 39.10 I 0.87 62.5 757 Silicon Si 28 28.3 IV 2.4 1450 3500 Silver Ag 108 107.88 I , 10.6 961 1955 Sodium Na 23 23.0 I 0.97 97.6 877 Strontium Sr 87 87.63 II 2.5 900 . . . rhombic Sulphur S 32 32.06 II IV VI 2.0 114.5 444.6 14*10 Tin Sn 119 118.7 IIIV 7.3 232 J.^Ov/ 1600 Zinc Zn 65 65.38 II 7.1 419 918 236 APPENDIX 11 QUIZ CO CO I-H CO CO | (-' CO CO HH HH CO HH PH IOAUS CO ^ HH CO ^ i * 1 ^ CC HH HH PH ^ CO rampog CO CO CO CO CO CO CO CO CO CO CO CO CO CO uraiannoj CO CO CO CO CO CO CO CO CO CO CO CO CO CO pnpMi CO CO HH | CO | HH CO CO HH HH CO HH HH ( ++ H ) ouno,8 M CO CO HH CO CO PH HH HH CO HH HH CO ^ | f Q \ v+ s HJ snojnojaj\[ ereutfinw CO CO HH | CO | HH CO CO HH PH CO HH | mmsauSfeH CO CO HH CO CO CO H-I CO CO HH HH CO CO PH 03 c3 p^ai (+++9^1) okudk! ! CO | | CO | HH CO HH HH CO | | (4-1.0 jj) snojjaj CO CO HH | CO | HH CO CO HH HH CO PH PH joddoj CO CO HH CO CO HH HH CO HH HH CO ^ CO ^qo D CO CO HH CO CO HH HH CO CO HH HH CO HH HH ranp^3 co co HH co co HH PH CO CO PH HH PH PH PH nmjmpB3 CC'CO HH CO CO | HH CO CO HH HH CO ^ CO i^Tinisig uinii'Bg; CO CO HH CO CO HH CO PH CO CO HH 3 CO HH snoiugsjy CO | | CO | CO PH | M 15 iuomnuy PH | | PH | PH PH 1 - 1 1 5 nmraoraray CO i/} CO CO CO CO CO CO CO | CO CO CO CO ranuicun^y CO /} | CO CO | HH O) CO M HH CO | | ^ \ \r