Synthetic Inorganic Chemistry

EXPERIMENTS 289

According to the equation, Na 2 CO 3 + H 2 CO 3 —• 2NaHCO 3 ,
56 cc. of carbon dioxide should be dissolved in this experiment.

(e) Repeat (c) using 10 cc. of lime water (saturated

Ca(OH) 2 solution) instead'of 5 cc. of 12V NaOH. Note

the appearance of the solution during and after the absorption.

Write equation to account for this appearance. What volume
of CO 2 should 10 cc. of saturated Ca(OH) 2 be able to absorb (the
Ca(0H) 2 is 0.02 molal) if (1) CaCO 3 is formed, (2) Ca(HCO 3 ) 2 is
formed?

(/) Bubble carbon dioxide slowly into a test tube of lime

water. A white precipitate forms at once but very soon

redissolves and the solution then remains clear.

As long as the base is in excess both stages of the ionization
of carbonic acid can proceed to completion because of the re-
moval of H+ ions (see Ionization of Polybasic Acids, Chapter III,
page 116),
Ca++ 2OH"
H 2 CO 3 ^H+ + HCO 3 -^CO 3 -- 2H+
1 1
CaCO 3 I 2H 2 O

but, as soon as the carbon dioxide is in excess, the concentration
of H+ ions from the first hydrogen of the carbonic acid is greater
than can exist in equilibrium with the CO 3 ~~ ions in a saturated
solution of calcium carbonate; hence the carbonate ions are re-
moved progressively and the solid continues to dissolve until the
solution is again clear.

CaCO 3 -»

H 2 CO 3 ^

Ca++

HCO,"

CO,"

H+

1

HCO 3 "

The components boxed in by the dotted lines represent the ionized

salt calcium bicarbonate present in the final solution.

2. Combustibility of Carbon Compounds. Place succes-
   sively a few drops of gasoline, carbon disulphide (CS 2 ), carbon
   tetrachloride (CCI4), and chloroform in a porcelain dish and
   apply a lighted match.