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


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.

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