c. Hydrogen iodide is still less stable than hydrogen bromide. What reaction would you expect to take place when concentrated sulfuric acid is added to a crystal of potassium iodide? (Compare c, Exercise 46.) Try the reaction and note any evidences in favor of your opinion.

d. The salts of hydriodic acid; the iodides. While hydriodic acid is unstable, its salts are stable. Study the properties of potassium iodide. Prepare a solution of the salt and study the action upon it of silver nitrate, as in the case of chlorides and bromides.

EXERCISE 48

HOW TO DISTINGUISH BETWEEN CHLORIDES,
BROMIDES, AND IODIDES

Apparatus. 3 test tubes.

Materials. 0.2 g. each of the chloride, the bromide, and the iodide of either potassium or sodium, dissolved separately in 5 cc. water; 5 cc. carbon tetrachloride; chlorine water (R. S.).

a. Recall the action of silver nitrate solution upon solutions of chlorides, bromides, and iodides (?).

b. Pour the solutions of the chloride, of the bromide, and of the iodide of potassium (or sodium) into separate test tubes and set the tubes in a rack in the order given.

Add to each solution 1 cc. of carbon tetrachloride (carbon disulfide will do as well but is inflammable). Shake the contents of the tubes and set them aside for two or three minutes (?). Add to each tube 2 or 3 cc. of chlorine water and shake again the contents of the tubes vigorously and set aside for a few minutes (?). Explain the action of the chlorine water.

The silver nitrate test will enable you to tell whether or not a given compound belongs to the group of chlorides, bromides, and iodides. The test with chlorine water and carbon tetrachloride will enable you to distinguish the three members of the group from one another.

EXERCISE 49

THE PREPARATION AND PROPERTIES OF CARBON MONOXIDE

Apparatus. The apparatus shown in Fig. 44: A is a funnel, connected by a rubber tube with a piece of glass tubing which passes through a stopper into the 250-cc. flask B; C is a small clamp; pneumatic trough; 3 wide-mouthed bottles; 3 glass plates 10 cm. square; burner; ring stand. Apparatus shown in Fig. 45: A and B are glass tubes connected by rubber tubing; C is a wide-mouthed bottle. Materials. Concentrated sulfuric acid; 25 cc. formic acid (50%); limewater (R.S.); 1 g. black copper oxide powder.

PRECAUTIONS. Carbon monoxide is a nearly odorless and very poisonous gas. All of the experiments must be performed in the hood. After the gas is generated, pour the contents of the generator flask into a sink or jar in the hood.

a. Remove the stopper from the flask B (Fig. 44), pour in 15 cc. of sulfuric acid and connect the apparatus as shown in the figure. Close the

clamp C and partially fill the funnel A with the formic acid. Now open the clamp carefully so that the formic

acid will enter the flask, a drop at a time. Allow 8 or 10 drops to flow in; then close the clamp. If the reaction does not begin (as indicated by

absence of efferves

D

B

FIG. 44

cence of the liquid in the flask and escape of gas through the exit tube), heat the flask very gently until the reaction starts; then open the clamp again and admit the formic

acid, a drop at a time, so as to secure a regular flow of gas from the flask. If necessary, add more formic acid to the funnel so as to keep it partially filled (?). Collect three bottles of the gas as shown in the figure. Close the clamp so as to stop further generation of gas. Slip the glass plates over the mouths of the bottles and remove the bottles from the trough. In the first bottle filled, is the gas pure carbon monoxide? Remove the glass cover and test it with a flame (?). Repeat with the second bottle filled (?). Slip the glass plate from the third bottle just far enough to pour into the bottle 5 cc. of clear limewater; then quickly replace

the glass plate and, holding it firmly against the mouth of the bottle, shake the contents of the bottle. Note any change in the appearance of the limewater. Now tip the bottle as far as pos

A

FIG. 45

B

C

sible without spilling the limewater; remove the glass plate and quickly ignite the gas, holding the bottle in this position so that at least a portion of the combustion product may be retained in the bottle. When the flame dies out, at once cover the mouth of the bottle with the glass plate and shake the contents. Note the results.

b. Introduce into the tube A, Fig. 45, a small amount of copper oxide and arrange the apparatus as shown in the figure. Now connect the exit tube D (Fig. 44) with the tube A (Fig. 45). Heat the copper oxide gently; at the same time pass a slow current of carbon monoxide through the tube, generating the gas as under a. Continue until the limewater and copper oxide both have visibly changed. Describe the results and write the equations for all the reactions involved.

EXERCISE 50

CARBONIC ACID AND ITS SALTS (CARBONATES)

Apparatus. Hydrogen generator, as used for preparing carbon dioxide in Exercise 19; small beaker; 5 test tubes.

Materials. Pieces of marble for generating carbon dioxide; hydrochloric acid; blue litmus paper; 5 cc. sodium hydroxide solution diluted with 10 cc. water; 1 g. of the common carbonates, such as sodium carbonate, magnesium carbonate, calcium carbonate; 25 cc. limewater (R.S.).

a. Generate carbon dioxide and pass the gas through 25 cc. of water. The gas combines with the water to form carbonic acid (R). Taste the liquid. Is the acid formed strong enough to affect blue litmus paper?

b. Pass carbon dioxide through a solution of sodium hydroxide until the gas is no longer absorbed; then evaporate the solution to dryness. Explain. Could a solution of sodium hydroxide be used in place of a solution of calcium hydroxide (limewater) in testing for carbon dioxide ?

c. Examine the physical properties of such carbonates as are available. What ones are soluble in water (p. 395 of text)? Test the action of hydrochloric acid or sulfuric acid on each by adding 1 or 2 drops of the acid to 0.1 g. of the carbonate on a watch glass. What evidences have you that a gas is evolved? Arrange a simple apparatus to determine whether or not the gas evolved is carbon dioxide, then test one or more of the carbonates.

All carbonates when treated with hydrochloric acid or sulfuric acid evolve carbon dioxide. This reaction serves as a good test for carbonates.

Can you suggest any reason why carbon dioxide is so readily liberated from carbonates?

EXERCISE 51

A STUDY OF SOME OF THE HYDROCARBONS

Apparatus. Evaporating-dish; burner; hard-glass tube fitted with a cork and a delivery tube, as shown in Fig. 20; two 250-cc. bottles; pneumatic trough; watch glass; beaker; stirring-rod; test tubes.

Materials. 15 g. soda lime (mixture of sodium hydroxide and calcium hydroxide); 10 g. fused sodium acetate; iron wire; bit of calcium carbide (size of a bean); sulfuric acid; sodium hydroxide; wooden splints; 10 cc. each of low-boiling gasoline and of kerosene ; 1 g. paraffin; 1 cc. of cottonseed oil.

*a. Methane. Intimately mix, by grinding together in a mortar, 15 g. of soda lime and 10 g. of fused sodium acetate. Transfer the mixture to the hard-glass tube used in preparing oxygen and proceed just as in the preparation of oxygen, « except that the tube should be clamped in a horizontal position while being heated. Collect over water one or two bottles of the evolved gas. Note the color and odor of the gas. Is it inflammable?

2

Sodium acetate has the formula NaC2H ̧O2 When heated with the sodium hydroxide, methane is generated according to the following reaction:

NaC H2O2+ NaOH - Na,CO,+CH

8 2

b. Acetylene. Nearly fill a test tube with water and drop into it a small piece of calcium carbide. Note the gas evolved (R). Ascertain by holding a lighted splint at the mouth of the tube whether the gas is inflammable.

c. Obtain from the instructor a few drops each of gasoline and of kerosene. Test the inflammability of each by dipping the end of a glass rod in the liquid and then touching it to the tip of a flame. Place ten drops of gasoline (PRECAUTION: keep away from all flames) on a watch glass (hood) and set the glass on a beaker half filled with boiling water.