The Foundations of Chemistry

DISSOLUTION OF GASES IN LIQUIDS

Based on Section 13-2 and the foregoing discussion, we expect that polar gases are most
soluble in polar solvents and nonpolar gases are most soluble in nonpolar liquids. Although
carbon dioxide and oxygen are nonpolar gases, they do dissolve slightly in water. CO 2 is
somewhat more soluble because it reacts with water to some extent to form carbonic acid,
H 2 CO 3. This in turn ionizes slightly in two steps to give hydrogen ions, bicarbonate ions,
and carbonate ions.

CO 2 (g)
H 2 O(
) 34 H 2 CO 3 (aq) carbonic acid (exists only in solution)

H 2 CO 3 (aq) 34 H
(aq)
HCO 3 (aq)

HCO 3 (aq) 34 H
(aq)
CO 32 (aq)

Approximately 1.45 grams of CO 2 (0.0329 mole) dissolves in a liter of water at 25°C and
one atmosphere pressure.
Oxygen, O 2 , is less soluble in water than CO 2 , but it does dissolve to a noticeable extent
due to dispersion forces (induced dipoles, Section 13-2). Only about 0.041 gram of O 2
(1.3 10 ^3 mole) dissolves in a liter of water at 25°C and 1 atm pressure. This is suffi-
cient to support aquatic life.
The hydrogen halides, HF, HCl, HBr, and HI, are all polar covalent gases. In the gas
phase the interactions among the widely separated molecules are not very strong, so solute–
solute attractions are minimal, and the dissolution processes in water are exothermic. The

14-4

Figure 14-4 The heat released by

pouring 50 mL of sulfuric acid,

H 2 SO 4 , into 50 mL of water

increases the temperature by 100°C

(from 21°C to 121°C)!

14-4 Dissolution of Gases in Liquids 549

Carbon dioxide is called an acid

anhydride, that is, an “acid without

water.” As noted in Section 6-8, part 2,

many other oxides of nonmetals, such

as N 2 O 5 , SO 3 , and P 4 O 10 , are also acid

anhydrides.

Aqueous HCl, HBr, and HI are strong

acids (Sections 4-2, part 2, and Section

10-7). Aqueous HF is a weak acid.