Gasses are soluble in liquid to different extents e.g., solubility of hydrochloric acid gas in water is much more than the solubility of oxygen in water.
Solubility of gas in a liquid depends on the following factors:1) Nature of the gas and the liquid
2) Temperature3) Pressure.
Nature of the gas and the liquid
Solubility of nonpolar bromine is much more in nonpolar solvents like carbondisulphide or carbontetrachloride than in water.
Temperature
Solubility of a gas in a liquid generally decreases with increase in temperature.
Pressure
Solubility of a gas in a liquid increases with the increase in partial pressure of the gas above the solution. Quantitatively, this is governed by Henrys law, which states that at constant temperature.
The mass of a gas dissolved in a given volume of the liquid is directly proportional to the pressure of the gas present in equilibrium with the liquid.
where 'm' is the mass of the gas dissolved in a unit volume of the solvent.
p is the pressure of the gas in equilibrium with the solvent.
k is the proportionality constant called Henry's law constant characteristic of the nature of the solvent and the natures of the gas, also the temperature.
Dalton also concluded independently that, solubility of a gas in liquid solution is a function of the partial pressure of the gas.
If mole fraction is used to represent the solubility of the gas in the solution, then
where, p is the partial pressure of the gas in solution, x is the mole fraction of the gas in solution and KH is Henry's law constant.
Here are the values of Henry's Law Constant (KH) for some selected gases in water
| Gas | Temp/K | KH/K bar |
|---|---|---|
| He | 293 | 144.97 |
| H2 | 293 | 69.16 |
| N2 | 293 | 76.48 |
| N2 | 303 | 88.84 |
| O2 | 293 | 34.86 |
| O2 | 393 | 46.82 |
It is obvious from the above table that the value of KH increases with temperature, indicating that solubility of gases decreases with increase in temperature.
Henry's Law explains many biological phenomena and also has several applications in industries, like:
1) To increase the solubility of CO2 in soft drinks and soda water, the bottle is sealed under high pressure.
2) In lungs the partial pressure of oxygen is high so haemoglobin combines with. oxygen to form oxohaemoglobin. But in the tissues the partial pressure of oxygen is low therefore oxohaemoglobin releases oxygen for utilization in cellular activities.
3) The breathing gas for deep sea divers consists of oxygen diluted with less soluble helium gas. This is to minimize the painful effects of deep sea divers due to decompression.
For e.g., concentration of CO2 which is dissolved in a carbonated beverage.
Example: Soda water is dependant directly on the partial pressure of CO2 in the gas phase.
4) Hydrogen bonding or dipole-dipole interaction between molecules of gas and molecules of the liquid. For e.g., dissolution of acetylene in acetone and dissolution of HCl in ether are due to hydrogen bonding.
