Common Ion Effect and Its application

CH₃COOH is a weak electrolyte that partially ionizes as

CH₃COOH ⇌ CH₃COO ^– + H⁺ ( weak electrolyte )

but, CH₃COONa is a strong electrolyte that almost completely ionizes as

CH₃COONa ⇌ CH₃COO^– + Na⁺

The addition of CH₃COONa to CH₃COOH solution introduces the large concentration of CH₃COO^– and the equilibrium of the former reaction gets disturbed by applying Le – Chatelier’s principle.

The ionization process of CH₃COOH gets suppressed by CH₃COO^–. This effect is called a common ion effect. Hence it is defined as the suppression of the ionization process of weak electrolytes by adding strong electrolytes having a common ion.

It is widely used in the qualitative inorganic salt analysis.