SOLUBILITY OF GASES IN WATERthiosulfate ion and found to be 1.0 10 ^3 mol dm^3 , then the concentration of
iodine in the tetrachloromethane layer must be 85 times as great:
concentration of I 2 in CCl 4 layer 85 1.0 10 ^3 8.5 10 ^2 mol dm^3Solvent extraction
Frequently in organic chemistry, it is necessary to separate an organic compound
from a watery mixture. This is done by adding an organic solvent (such as dichloro-
methane or ethoxyethane) and shaking – a process called solvent extraction. The
organic solvent contains most of the desired organic compound (the solute) and the
compound is obtained by evaporation of the organic layer. The arithmetic of solvent
extraction is discussed in Chapter 19.
Chromatography
One of the most important ways of separating mixtures, known as chromatography,
is really a series of solvent extractions. More details are given in Chapter 19.
Solubility of gases in water
The solubilities of common gases are given in Table 11.5. Some gases (e.g. H 2 , O 2 ,
N 2 , CH 4 ) are only slightly soluble in water. The dissolution of these gases may be
represented by the equation
water
gas molecules \===\dissolved moleculesThe dissolved gas may be driven out of solution by heating.
Other gases (e.g. NH 3 , HCl, NO 2 )chemically reactwith water. These gases are
generally more soluble than H 2 , O 2 , etc. The dissolution of such gases may be
thought of as occurring in two stages:
water water
gas molecules \===\dissolved molecules \===\products11.5
183Table 11.5Solubilities of common gases at 0 °C. The
pressure of the gases in contact with the water is 1 atmGas Solubility of gas/m^3 of
gas per m^3 of water
Helium He 0.0094
Hydrogen H 2 0.021
Nitrogen N 2 0.024
Carbon monoxide CO 0.035
Oxygen O 2 0.049
Methane CH 4 0.054
Argon Ar 0.056
Carbon dioxide CO 2 1.7
Chlorine Cl 2 4.6
Hydrogen sulfide H 2 S4.7
Sulfur dioxide SO 2 80
Hydrogen chloride HCl 506
Ammonia NH 3 1300
The bioconcentration
of pesticides
requires a knowledge
of distribution ratio.
See Appendix 19 on
the website.