CHAPTER XIV

CARBON AND ITS COMPOUNDS

111. Carbon. a. Arrange an apparatus as shown in Fig. 41. Partly fill the hard-glass test tube A with small pieces of wood — preferably with hardwood sawdust. Heat the wood, gently at first and then more strongly. After some liquid has collected in B, apply a light to the jet C. Are combustible gases evolved on distilling wood? Continue the heating as long as gas is evolved, then examine the liquid collecting in B. Is it soluble in water? What is its reaction toward litmus ? How would you describe its odor? What is the residue left in 4? Will it burn? Does it leave any ash?

b. Bring a cold porcelain dish into a small, luminous Bunsen flame. Note the de

FIG. 41

B

posit. What is this form of

carbon called? In what other forms does carbon exist? What properties have all these forms in common?

c. Put one fourth of a test tube full of bone black into a small flask and pour over it about 50 cc. of water, to which has been added a few drops of a solution of litmus or of indigo. Thoroughly mix the contents of the flask, then heat it gently for a few minutes and filter. If the filtrate is not

decolorized, repeat, 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 at ordinary temperatures an active element? Test it with the common acids. How does the charring of wood preserve it?

e. Prepare an apparatus according to Fig. 42. The bottle A contains a solution of sodium hydroxide, while B and C contain a solution of calcium hydroxide (limewater). The hardglass tube D contains one or two small pieces of charcoal. Charge your oxygen generator as in § 15 and connect the rubber delivery tube with E. Now pass a slow current of oxygen through the apparatus, at the same time heating the charcoal in D until it just begins to glow. Describe the results. What do they

prove? Why pass the oxygen through the solutions in A and B? What reactions take place in D and C (R)?

f. In a hard-glass test tube heat an intimate mix

E

D

ture of 2 or 3 g. of black copper oxide and an equal bulk of powdered charcoal. Pass the evolved gases through a little limewater in a test tube. Write all the equations involved in the reactions. What remains in the test tube? How can you prove it? What use does this suggest for charcoal?

112. Carbon dioxide. a. Put some pieces of marble in your hydrogen generator, cover them with water, and add a little concentrated hydrochloric acid through the funnel tube. Fill two or three bottles with the gas evolved by downward displacement. (To test whether the bottles are filled or not, hold a burning splint in the mouth of the bottle.)

b. 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.

c. Half fill a small beaker with limewater and pass carbon dioxide through the liquid (R). Continue until the precipitate which at first forms is dissolved (R), and then divide the solution into two parts. To the one add a little clear limewater (R); to the other apply heat until it boils rapidly (R). The formation of a white precipitate in limewater is a test for carbon dioxide.

d. Prove the presence of carbon dioxide in the air exhaled from the lungs by blowing through limewater (R). Hold a wide-mouthed bottle above a small flame so that the hot gaseous products of combustion will collect in it; then quickly add a few cubic centimeters of limewater, cover the mouth of the bottle with the hand, and shake up the contents. What do the results prove? What are the sources of carbon dioxide in the air? Does the percentage in the air increase? Why?

e. Wash the gas by bubbling it through water, and then pass it through pure water in a beaker until the gas is no longer absorbed. Test the solution with litmus. How does the taste of the solution compare with that of water?

113. Weight of 1 liter of carbon dioxide. The weight of 1 liter of carbon dioxide may be determined by a suitable modification of the method employed for ammonia (§ 75). Should the gas be dried? How may this be done? Should the gas be absorbed in water or in a solution of an acid or of an alkali? Submit your plan to the instructor and then proceed with the determination.

114. Carbonates. a. Give the formula and properties of the acid of which the carbonates are salts. Try the action of hydrochloric acid on a small amount (about 1 g.) of each of the following carbonates: sodium carbonate, potassium carbonate, magnesium carbonate (R). How can you detect the presence of carbonates? Is limestone a carbonate? Is the action of sulfuric and nitric acids on carbonates similar to that of hydrochloric acid (R)? Why is carbonic acid so readily liberated from carbonates?

b. Pass a current of carbon dioxide through 10 cc. of the laboratory solution of sodium hydroxide (1 part of sodium