EXERCISE 16

STATES OF MATTER

Apparatus. Watch crystal; 500-cc. beaker; thermometer graduated to at least 110°; ring stand and burner.

Materials. 1 cc. ether or chloroform; 10 cc. benzene; pieces of ice.

a. Place about 1 cc. of ether or of chloroform on a watch crystal and blow upon the surface of the liquid. Account for the rapid evaporation. Do you notice any change in the temperature of the watch glass? Explain.

b. Pour about 250 cc. of distilled water into a suitable flask or beaker, and place a thermometer in the liquid so that the temperature may be noted. Now heat the water at such a rate that the temperature rises slowly but steadily. At what temperature do you observe the formation of bubbles? Where do they appear to form? Of what are they composed? At about what temperature do larger bubbles begin to form at the bottom of the vessel? What becomes of them? Explain. At what temperature do they move freely up through the liquid to the surface? Do they get larger or smaller as they rise? Why? When the water is gently boiling, try increasing the heat. Is the boiling any more energetic? Does the temperature rise any? How do you define the boiling point?

c. Pour about 10 cc. of benzene into a clean, dry hardglass test tube. This liquid is inflammable and must be kept away from all flames. Pour into a beaker some ice water in which some pieces of ice are floating. Now immerse in this ice water that part of the test tube which is filled with benzene. Stir the benzene constantly with a thermometer, noting the temperature from time to time. Carefully note the temperature when the benzene begins to freeze and continue the reading until the entire liquid, or nearly all of it, is frozen. Now remove the tube from the ice water and hold the lower

part of it in the hand until the benzene is melted, noting the temperature during this change. Note the results and discuss.

d. Experiment c may be repeated, using water in the test tube and immersing it in a freezing-mixture made by mixing 3 parts of powdered ice with 1 part of common salt.

EXERCISE 17

THE FORMATION OF CHARCOAL AND COKE

Apparatus. Hard-glass test tube A connected as shown in Fig. 29; B is a test tube fitted with a glass tube C drawn to a jet; large beaker; porcelain dish; burner.

Materials. Small pieces of hard wood (sawdust will do) sufficient to half fill the hard-glass test tube; pieces of soft coal sufficient to half fill the test tube; blue and red litmus paper.

a. Half fill the tube A (Fig. 29) with hard-wood splints or sawdust and connect it as shown in the figure. The tube B is kept cool by ice water in the beaker. Heat the wood in A, gradually increasing the heat until no further change takes place. During the heating, test the gas escaping from the jet C to determine whether it will burn (?).

When the tube A is cool, remove the residue (?). Note its properties. Is it combustible?

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Note the odor and appear

ance of the liquid condensed

FIG. 29

in B. Name two important compounds prepared commercially from the liquid obtained by heating hard wood in the

absence of air (p. 121 of text). What name is applied to the process undergone by the wood?

b. Repeat experiment a, substituting small pieces of soft coal for the wood. Describe the results. What is left in the tube A? The liquid condensed in B is known as coal tar (p. 306 of text). Note its appearance and odor.

EXERCISE 18

A FURTHER STUDY OF CARBON

Apparatus. Hard-glass test tube; porcelain dish; burner; funnel. Materials. 3 g. sugar; test tube one-fourth full of bone black; 1 cc. litmus solution; filter paper; common acids; 3 g. copper oxide and an equal bulk of powdered charcoal; 5 cc. limewater (R.S.).

a. Heat 2 or 3 g. of sugar in a test tube until no further change takes place. Note the results. What is the residue? b. Bring a cold porcelain dish into a small luminous Bunsen flame. Note the deposit. What is this form of carbon called? In what other forms does carbon exist?

c. Put into a small flask enough bone black to fill a test tube one-fourth full and pour over it about 50 cc. of water, to which has been added a few drops of a solution of litmus or indigo. Thoroughly mix the contents of the flask; then heat gently for a few minutes, and filter. If the filtrate is not decolorized, repeat the process, using more bone black. What is the composition of bone black? By what other name is it known? What use does this experiment suggest for it?

d. Is carbon an active element at ordinary temperatures? Test it with the common acids. How does the charring of wood preserve it?

e. Mix together in a mortar 2 or 3 g. of black copper oxide and an equal bulk of powdered charcoal. Transfer to a hardglass test tube and heat gently. The copper oxide is reduced to copper, the oxygen combining with the hot carbon to form carbon dioxide.

EXERCISE 19

A STUDY OF CARBON DIOXIDE

Apparatus. Hydrogen generator with connections, as shown in Fig. 30; three 250-cc. bottles; small beaker or test tube; hard-glass test tube.

Materials. 5 pieces of marble (size of walnuts); hydrochloric acid; splints; limewater (R. S.); 3 g. of copper oxide and an equal bulk of powdered charcoal.

a. Usual laboratory method for preparing carbon dioxide. Place some pieces of marble in your hydrogen generator and connect as shown in Fig. 30. Add water through the funnel tube until the marble is covered with the liquid; then add hydrochloric acid, a few drops at a time. Collect three bottles of the gas by displacement of air. To test when filled, hold a burning splint at the mouth of the bottle; the gas will extinguish the flame. Why not collect the gas over water as in the case of oxygen and hydrogen?

FIG. 30

B

b. Thrust a burning splint into one of the bottles of the gas (?). The results suggest what use for the gas?

c. Devise an experiment to show whether the gas is heavier or lighter than air. Attempt to pour it from one bottle to another, as you would a liquid, and test with a burning splint for its presence in the second bottle (?).

d. Pass a few bubbles of the gas through 10 cc. of limewater (?). This serves as a good test for carbon dioxide.

e. Prove that the air exhaled from the lungs contains carbon dioxide; also prove that it is formed when ordinary fuels burn.

*f. Repeat experiment e, Exercise 18, and prove that carbon dioxide is evolved.

EXERCISE 20

PREPARATION AND PROPERTIES OF NITROGEN

Apparatus. 250-cc. flask, with cork and glass delivery tube, like that used in preparing oxygen (B, C, Fig. 20); ring stand; burner; pneumatic trough; 3 wide-mouthed bottles.

Materials. 3 g. ammonium chloride; 6 g. sodium nitrite.

a. Recall experiment b, Exercise 4. What is the gas left in the beaker after the combustion of the phosphorus ?

b. In a 250-cc. flask introduce a mixture of 3 g. of ammonium chloride and 6 g. of sodium nitrite, and add 20 cc. of water. Provide the flask with a one-hole cork and delivery tube so that the evolved gas may be collected over water, as in the case of oxygen and hydrogen. Have at hand a vessel of cold water so that the flask may be cooled by lowering it into the water in case the action becomes too violent.

Clamp the flask and apply a very gentle heat, moving the burner about with the hand. As soon as the action begins, withdraw the heat. After the air has been expelled from the apparatus, fill three bottles (250-cc.) with the gas. If the action becomes too violent, immerse the flask in cold water. Write the equations for the reactions involved (p. 130 of text).

Note the physical properties of the gas. Can it be poured from one bottle to another as in the case of carbon dioxide ? Is the gas combustible (test with burning splint)? Is it a supporter of combustion ?