Question

explain common ion effect?

Answer 1

When in an ionic equilibrium a salt containing common ion is added then equilibrium shift in backward direction.
eg CH3COONA IS ADDED TO CH3COOH

Answer 2

$\textbf{\large{Answer -}}$

To the solution of weak electrolyte a salt solution having common ion is added then the dissociation of weak electrolyte is suppressed. This effect is known as $\textbf{commom ion effect.}$

For Example :

In presence of $CH_{3}COONa$ , dissociation of $CH_{3}COOH$ is suppressed.

Explanation :

$CH_{3}COOH$ is weak electrolyte and are dissociated as follow -

$CH_{3}COOH (aq) ==> CH_{3}{COO}^{-} + {H}^{+}$

$CH_{3}COONa$ is a strong electrolyte and are dissociated as follow -

$CH_{3}COONa ==> CH_{3}{COO}^{-}+ {Na}^{+}$

Due to presence of common ion i.e., $CH_{3}{COO}^{-}$ ion, the concentration of $CH_{3}{COO}^{-}$in solution is increased and according to Le-Chatelier Principle, the equilibrium will shift in backward direction i.e., dissociation of acetic acid is suppressed.