Common ion effect
Le Chatelier's Principle helps to explain common ion effect. According to LeChatelier's Principle, if an equilibrium gets out of balance it will shift to restore the balance. When a common ion is added to a weak acid or weak base equilibrium, then the equilibrium will shift towards the reactants, the weak acid or base. When a common ion is added to that solution, ionization of an acid or base is decreased. Common ion effect is the shift in equilibrium caused by the addition of an ion that takes part in the equilibrium.
The suppression of the solubility of a weak electrolyte in the presence of strong electrolyte, which contains common ion is called common ion effect.
1. The solubility of NaCl decreases in the presense of HCl. Cl- ion is common in both the substances.
2. The degree of ionization of acetic acid decreases in the presense of HCl. H3O+ ion is common ion.
Applications of common ion effect:
- Common ion effect is used in the controlling the H+ concentration in buffer solutions.
- It is used in qualitative analysis of cations.
- Common ion effect is used in the purification of common salt by passing dry HCl gas.