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Chapter V


85. Formation of Formic Acid by the Oxidation of Methyl Alcohol (Section 80). - Place in a 100 cc. distilling flask, 5 grams of powdered potassium bichromate, 20 cc. of water, and 5 cc. of concentrated sulphuric acid. Cool the flask, and add slowly with shaking 2 cc. of methyl alcohol drop by drop, keeping the flask under water. Place the flask for about 10 minutes in a beaker containing boiling water. Distil off, using a condenser, about 10 cc. of liquid. Apply to the distillate tests described in experiment 87b and c below. Write equations for all reactions involved.

86. Preparation of Formic Acid from Oxalic Acid (Section 80). - Into a 250 cc. distilling flask, provided with a condenser and receiver, put 20 grams of anhydrous glycerol and 20 grams of oxalic acid. Close the flask by a cork carrying a thermometer which is so placed that the bulb is below the surface of the glycerol. Heat cautiously with a small flame. Carbon dioxide is given off at about 80°. Maintain the temperature at 105°-110° until the evolution of gas has slackened. Cool the contents of the flask to about 60°, add 20 grams more of oxalic acid, and heat as before. Repeat the addition of oxalic acid until 80 grams in all of the acid have been used. After the last portion of the acid has been added, allow the temperature to rise to 115°. A dilute aqueous solution of formic acid is obtained. (Eq.)

87. Properties of Formic Acid (Section 80). - (a) Odor of formic acid. - Note the odor of the solution obtained in experiment 86 above, and test the solution with blue litmus paper.

(b) Reduction of silver formate. - Neutralize 2 cc. of the dilute solution of formic acid with ammonia. Add a few drops of a solution of silver nitrate, and warm carefully. (Eq.)

(c) Reduction of mercuric formate. - Shake for about 1 minute 2 cc. of the distillate with 0.2 gram of mercuric oxide. Filter the solution and heat it to boiling. The mercuric formate first formed is reduced to mercurous formate, and finally to mercury. (Eq.) This is a valuable test for formic acid.

(d) Reduction of mercuric chloride by formic acid. - To 5 cc. of the distillate add 2 cc. of a solution of mercuric chloride and heat. The mercuric chloride is reduced to mercurous chloride. (Eq.)

(e) Decomposition of formic acid by sulphuric acid. - To 2 cc. of the distillate add 2 cc. of concentrated sulphuric acid slowly and heat gently. (Eq.) Apply a flame to the liberated gas. If an inflammable gas is not obtained, repeat using 0.5 gram of sodium formate.

(f) Oxidation of a formate. - Neutralize 1 cc. of the distillate with a dilute solution of sodium hydroxide. Add, drop by drop, a dilute (rose-colored) solution of potassium permanganate. (Eq.) What is the significance of the result when compared with the action of unsaturated hydrocarbons with potassium permanganate? (See experiment 72d, page 50.)

(g) Salts of formic acid. - Dilute what is left of the distillate with an equal volume of water and divide it in two portions; boil one for about 5 minutes with an excess of lead oxide, and the other with copper oxide. Filter the solutions while still hot and set aside to crystallize.

88. Formation of Acetic Acid from Ethyl Alcohol (Section 85), - To 15 grams of coarsely powdered potassium bichromate contained in a 200 cc. round-bottomed flask, add a mixture of 15 grams of concentrated sulphuric acid and 10 cc. of water. Set the flask on a sand-bath and connect it with a reflux condenser through which a rapid stream of water is passing. Add through the condenser slowly, in portions of 0.5 cc., 3 cc. of alcohol. Shake after each addition and wait until the vigorous reaction which takes place subsides before another addition of alcohol is made. When all the alcohol has been added, heat to boiling for 15 minutes. Change the condenser and distil off about 10 cc. (Eq.) Observe the odor of the solution (see note) and test it for acetic acid by experiment 91a and b below.

Note. - There is usually present in the distillate ethyl acetate and aidehyde, both of which have a characteristic odor. A mixture of potassium bichromate and sulphuric acid (chromic acid) is an excellent oxidizing agent to use in the preparation of acetic acid by oxidation, since acetic acid is not readily oxidized by chromic acid.

89. Preparation of Glacial Acetic Acid (Section 83). - Melt cautiously in an iron dish about 50 grams of anhydrous sodium acetate[1]. Grind the salt to a coarse powder in a mortar; weigh 40 grams of the salt and place it in a 200 cc. distilling flask. Add cautiously through a funnel, keeping the flask cold by immersion in water, 25 cc. of concentrated sulphuric acid. Place a thermometer in the flask in order to determine the temperature of the vapor. Connect with a condenser and receiver, and distil off the acetic acid. Weigh the acid obtained. Calculate the theoretical amount which can be obtained from 40 grams of sodium acetate, and the percentage yield of the experiment. Caution. - Glacial acetic acid causes painful blisters when left in contact with the skin.

90. Properties of Acetic Acid (Section 87). - (a) Solubility of acetic acid. - Test the solubility of acetic acid in water, alcohol, ether, and benzene. Place about 10 cc. of the acid obtained in a test-tube surrounded by chipped ice and water. Insert a thermometer into the acid. If crystals do not form, scrape the side of the tube with a glass rod. If the acid freezes, remove the tube, stir with the thermometer, and note the temperature when the acid is about one-fourth melted[2]. Pure acetic acid melts at 16.7° and boils at 119°. One per cent of water lowers the melting-point about 2.1°.

(b) Acetic acid and oxidizing agents. - Determine whether acetic acid reduces solutions of potassium permanganate, silver nitrate, and mercuric chloride. Compare the results with those obtained with formic acid. (Experiment 87, page 61.)

(c) Add a few crystals of chromic acid to a mixture of 5 cc. of glacial acetic acid and 2 cc. of water. Heat to boiling. Is the chromic acid reduced?

(d) Formation of verdigris. - Stand a piece of copper foil in a small beaker containing acetic acid; a part of the foil should be under the liquid and a part exposed to the air. Examine the foil at the next exercise. What is formed?

91. Tests for Acetic Acid (Section 89). - (a) Formation of basic ferric acetate. - Add a few drops of a solution of ferric chloride to a solution of sodium acetate. Note the color. Heat the solution to boiling. The neutral ferric acetate is converted into a basic acetate. (Eq.) In using this test for the free acid it must first be neutralized with sodium hydroxide.

(b) Formation of ethyl acetate. - Repeat the test involving the formation of ethyl acetate given in experiment 81a, page 57.

(c) Conversion of acetic acid into acetanilide. - Place in a dry test-tube 0.6 gram of anhydrous sodium acetate, 0.25 cc. of concentrated sulphuric acid, 1 cc. of aniline. The substances used should be measured accurately. Close the mouth of the tube with a cork bearing a piece of glass tubing about 2 feet long. Support the tube in a vertical position and heat it so the contents boil gently for about 1 hour. Cool, dissolve the product in 25 cc. of boiling water, filter hot, and set aside to crystallize. Determine the melting-point of the crystals. Acetanilide melts at 116°.

Note. - (c) The identification of a substance is best accomplished by converting it into a solid which has a definite melting-point and can be readily purified. In the case of acetic acid and its homologues the anilides serve this purpose well (Section 416). They are formed as the result of the elimination of water from the acid and aniline:


If the acid to be identified is dissolved in water it is neutralized with sodium hydroxide and the solution evaporated to dryness. The salt is cautiously heated over a free flame to drive out the water of crystallization; it is then heated with aniline and enough concentrated sulphuric acid to set free the organic acid. When salts are used the reaction is as follows:


92. Preparation and Properties of Soap: Saponification of Fat (Section 96). - (a) Melt 35 grams of lard in a casserole and add slowly, with constant stirring, 10 cc. of a strong solution of sodium hydroxide made by dissolving 1 part of sodium hydroxide in 1 part water. When an emulsion has formed, heat the mixture cautiously over a low flame, stirring it until it begins to boil. Continue the heating until the mixture becomes homogeneous. If spattering can not be avoided, heat the casserole on a steambath. Pour the soap into a beaker, and allow it to stand for several days. The chief constituents of lard are the glyceryl esters of palmitic, stearic, and oleic acids. Write equations for the reactions which take place when these three substances are heated with sodium hydroxide.

(b) Test for free alkali in soap. - Determine whether the soap prepared in (a) above contains free alkali, as follows: Dissolve a small piece of the soap in cold water and test the solution with a solution of phenolphthalein.

(c) Hydrolysis of soap. - Shake vigorously a piece of Ivory soap about the size of a large pea with 10 cc. of cold water. Filter and test one-half of the solution with a solution of phenolphthalein. How do you explain the difference between the result of this experiment and that obtained with the soap you prepared? Heat to boiling the other half of the solution of Ivory soap and add phenolphthalein. Explain and write equations for the reaction.

(d) Soft soap. - Cut the soap you prepared into thin shavings and heat it with 400 cc of water until it dissolves. Divide the product into four parts. Put aside one of these and allow it to cool. Describe the properties of the soft soap.

(e) Salting out of soap. - Precipitate one portion of the solution by adding slowly, with stirring, an equal volume of a saturated salt solution. Filter off the precipitate and save the filtrate for another experiment. Wash the precipitate with 50 cc. of saturated salt solution, let it drain thoroughly, and finally spread it on a watch-glass to dry. Test the soap for free alkali as in (b) above. From what organic compound has the soap been separated by this treatment?

(f) Solubility of soap. - Test the solubility of the purified soap in water, in alcohol, and ether. This can be done most readily by shaking pieces of the soap with about 15 cc. of each of the solvents, filtering, and evaporating the solvents on a water-bath. If there is any residue from the ether, test it to determine whether it is soap, or fat which has not saponified.

(g) Action of hard water and soap. - To determine the action of hard water on a solution of soap, add to small portions of the solution prepared in (d) above, solutions of calcium chloride and magnesium sulphate. (Eq.) Test the solubility of the precipitates in water. Explain the difference between the action of sodium chloride and calcium chloride on a soap solution. Did you note any difference in the action of the two salts on a dilute solution of soap? What chemical compounds may be present in natural hard water?

(h) Isolation of fatty acids from soap. - To the remainder of the solution prepared in (d) above, add dilute hydrochloric acid as long as a precipitate is formed. Of what does this precipitate consist? (Eqs.) Filter and wash with cold water; drain thoroughly and spread the precipitate on a watch-glass to dry. Test the solubility of the precipitate in water, sodium hydroxide (Eq.), ether, and alcohol. Place a small piece of the precipitate in a test-tube one-half full of water; heat to boiling and shake. Describe the appearance. Cool and shake. What is the effect of hot water on the acids? On the basis of their solubility, state how you could separate into its constituents a mixture which contained fat, fatty acids, and soap.

(i) Test for unsaturated acids in soap. - Dissolve about 1 gram of the acids obtained in experiment (h) above in 5 cc. of carbon tetrachloride and add, drop by drop, a solution of bromine in carbon tetrachloride. Explain. (Eq.)

(j) Identification of glycerol in the product of the hydrolysis of fat. - The presence of glycerol can be shown as follows: Neutralize with dilute hydrochloric acid about 100 cc. of the solution reserved in experiment (e) above; filter, evaporate the filtrate to dryness, and stir the residue of salt and glycerol with about 20 cc. of alcohol. Decant off the liquid through a filter and evaporate on the steam-bath. A sample of impure glycerol will be left. Prove the presence of glycerol by applying two of the tests given in experiment 84, page 59.

Notes. - (e) If one precipitation does not free the soap from alkali, redissolve it and precipitate again.

(f) Ether dissolves fat but does not dissolve soap; this solvent can be used, therefore, to determine the presence of unsaponified fat in a sample of soap.

93. Preparation and Properties of Oxalic Acid (Sections 106, 108). - (a) Heat on the steam-bath in an open 500 cc. flask 120 grams of concentrated nitric acid (sp. gr. 1.42) and 20 grams of cane-sugar. As soon as brown fumes begin to be evolved, place the flask in a hood, and let it stand until the rapid evolution of oxides of nitrogen ceases. Evaporate on the steam-bath until the volume of the liquid is reduced to about 30 cc. Set aside to crystallize. Filter off the acid through a funnel provided with a perforated plate, using no filter-paper. Dissolve the crystals in the smallest amount of boiling water possible, and set the solution aside to crystallize. Oxalic acid dissolves in 10.46 parts of water at 14.5°. Weigh the product obtained.

(b) Action of heat on oxalic acid. - Heat about 1 gram of oxalic acid in a dry test-tube; continue the heating after the water of crystallization has been driven off. Describe the result. Oxalic acid, (COOH)2.2H2O, melts at 99°; the anhydrous acid sublimes at 150°-180°.

(c) Change of a formate to an oxalate. - Heat in a dry test-tube about 1 gram of sodium formate. (Eq.) Apply a flame to the gas evolved. Test the residue for an oxalate according to experiment 94c below.

(d) Potassium tetroxalate. - Dissolve 5 grams of oxalic acid in 30 cc. of hot water. Neutralize exactly one-fourth of this solution carefully with a solution of potassium hydroxide (1:4); combine the solutions and set aside to crystallize. (Eq.) When cold, filter off the salt. Dissolve a little of the salt in water, and try its effect on an iron-rust stain, also on a spot made with an iron ink and an ink made from an aniline dye.

(e) Potassium ferric oxalate. - Add to a solution of ferric chloride a solution of potassium oxalate until a clear green solution is formed. (Eq.) Moisten a piece of paper with the solution. Test the paper for a ferrous salt by putting on it a drop of potassium ferricyanide. Expose a piece of the paper to direct sunlight for 1 minute and test again for a ferrous salt.

94. Tests for Oxalic Acid and Oxalates (Sections 106, 108). - (a) Oxalic acid and sulphuric acid. - Heat about 2 grams of oxalic acid with about 5 cc, of concentrated sulphuric acid. (Eq.) Pour some of the gas formed into a test-tube containing a solution of barium hydroxide, and shake. Ignite the gas which is produced in the reaction. How could you prepare carbon monoxide free from carbon dioxide by making use of this decomposition? What other acid yields carbon monoxide when heated with sulphuric acid?

(b) Silver oxalate. - In a test-tube neutralize a solution of oxalic acid with ammonia; if a slight excess of ammonia is added, boil the solution until it is neutral to litmus. Cool and add a solution of silver nitrate. A precipitate of silver oxalate is formed. (Eq.) Heat to boiling. Compare the results with those obtained with formic acid (experiment 87b, page 61).

(c) Precipitation of calcium oxalate. - To a solution of oxalic acid add ammonia in slight excess, and then a solution of calcium chloride. (Eq.) Test the solubility of the precipitate in a solution of acetic acid and in dilute hydrochloric acid. How would calcium carbonate act when treated with acetic acid?

(d) Reducing action of oxalic acid - To a solution of oxalic acid or an oxalate add dilute sulphuric acid and a solution of potassium permanganate. (Eqs.)

(e) Repeat (d), using a solution of potassium bichromate in place of one of potassium permanganate. (Eqs.)

[1] If the anhydrous salt is not available, dehydrate the crystalline salt for this experiment according to the directions given in experiment 66a, page 43.

[2] If the acid prepared does not freeze, determine the melting-point, as described above, of a sample of glacial acetic acid.

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