Question

Which of the following pairs will show common ion effect?

• A. Barium chloride + barium sulphate
• B. Silver cyanide + potassium nitrite
• C. Ammonium hydroxide + ammonium chloride
• D. Sodium chloride + hydrogen chloride

Answer 1

The correct option is C Ammonium hydroxide + ammonium chloride

The suppression of the dissociation of weak acid/base on the addition of its own ion is called the common ion effect.

Ammonium hydroxide is a weak base and it can be dissociated as,

$N{H}_{4}OH+HCl\rightleftarrows N{H_4}^{+}+O{H}^{-}$

Ammonium chloride is a salt and it is obtained from a neutralization of weak base and strong acid
($N{H}_{4}OH+HCl$) . Ammonium chloride can be dissociated as,

$N{H}_{4}Cl\rightleftarrows N{H_4}^{+}+C{l}^{-}$

On $N{H}_{4}OH$ and $N{H}_{4}Cl$ , $N{H_4}^{+}$ $N{H_4}^{+}$ (Ammonium ion) is common and thus, it suppresses the dissociation of ammonium hydroxide as per Le Chatelier's principle.

Thus, ammonium hydroxide and ammonium chloride show a common ion effect.