Solubility of gases in liquids: All gases are less or more soluble in water or soluble in certain limit and form a true solution. The volume (in mL) of a gas which dissolved in 1 mL of water is called absorption coefficient.The solubility of gases in liquids is affected by the following factors:
1. Nature of gas: The gases which react with solvent or ionized in solution are soluble in water. e.g. NH3, HCl(g) and SO2 are more soluble in water and form NH4OH, HCl(l) and H2SO4 compounds respectively.
2. Nature of solvent: The polar gases are soluble in polar solvent while non-polar gases are soluble in non-polar solvents. It is like dissolves like rule e.g. HCl gas is more soluble in water than liquid benzene.
3. Effect of Temperature: Temperature has a marked effect on the solubility of a solid in liquid. The solubility may increase or decrease with the rise in temperature depending upon the value of ∆sol H < 0. Let us recall, that saturated solution represents equilibrium between undissolved solute and dissolved solute.
Solute + Solvent ⇌ Solution; ∆sol H = ± x
(i) If the value of ∆sol H < 0 i.e. the solution process is exothermic, then according to Le-chatelier’s principle, the increase of temperature will push the solution equilibrium in the backward direction. In other words, the solubility of solutes decreases with rise in temperature. Some examples are Li2SO4, Na2SO4 etc.
(ii) If ∆sol H > 0, i.e. solution process is endothermic, then increase of temperature will push solution equilibrium in the forward direction. In other words, the solubility of such solutes increases with the rise in temperature. Some examples of such solutes are KCI, KNO3, NaNO3 etc.
4. Effect of pressure: The solubility of gases is much affected by change in pressure. Henry proposed a relationship between pressure (P) and the composition of solution which is called Henry’s law. According to this law.
“At constant temperature, the amount of gas soluble in unit volume of solvent is directly proportional to pressure created by gas at equilibrium on the surface of solvent”.
If the mass of gas is m which is dissolved in unit volume 3 of solvent at pressure (P) then according to Henry’s law,
m ∝ P
m = kP
k = Henry constant
