Explain the solubility of a solution formed by a gaseous solute and a liquid solvent.

(N/A) The solubility of a gas is the maximum amount of gaseous solute that can be dissolved in a specified amount of solvent at a specified temperature and pressure.
Oxygen dissolves only to a small extent in water. It is this dissolved oxygen which sustains all aquatic life. On the other hand,hydrogen chloride gas $(HCl)$ is highly soluble in water.
The solubility of gases in liquids is greatly affected by pressure and temperature.
$(i)$ Effect of pressure: The solubility of gases increases with an increase in pressure. For a solution of gases in a solvent,consider a system as shown in Fig. $(a)$. The lower part is the solution and the upper part is the gaseous system at pressure $P$ and temperature $T$. Assume this system to be in a state of dynamic equilibrium,i.e.,under these conditions,the rate of gaseous particles entering and leaving the solution phase is the same.
Now,increase the pressure over the solution phase by compressing the gas to a smaller volume [Fig. $(b)$]. This will increase the number of gaseous particles per unit volume over the solution and also the rate at which the gaseous particles are striking the surface of the solution to enter it. The solubility of the gas will increase until a new equilibrium is reached,resulting in an increase in the pressure of the gas above the solution and thus its solubility increases.
$(ii)$ Effect of temperature: The solubility of gases in liquids decreases with an increase in temperature. When gases dissolve,they enter the liquid phase,and the phenomenon of dissolution is called condensation. This process is exothermic in nature. Therefore,on increasing the temperature,the solubility decreases.