Question

If ammonium chloride is added to a solution of ammonium hydroxide in water, then:

• A. ammonium hydroxide is neutralized
• B. ammonium is liberated
• C. dissociation of ammonium hydroxide increases
• D. dissociation of ammonium hydroxide is reduced

Answer 1

The correct option is D dissociation of ammonium hydroxide is reduced

Due to the addition of $N{H}_{4}Cl$ which is strongly ionised in solution the concentration of $N{H}_4{}^{+}$ ions increases in the solution, therefore, according to Le-Chatelier's principle, equilibrium equation (1) shifts in the backwards direction in favour of unionised $N{H}_{4}OH$.

In this way, an addition of $N{H}_{4}Cl$ suppresses the degree of ionisation of $N{H}_{4}OH$. Thus, concentration ions $O{H}^{-}$ in the solution is considerably reduced and the weak base $N{H}_{4}OH$ becomes a weaker base.

The suppression of the degree of ionisation of a weak electrolyte (weak acid or base) by an addition of some strong electrolyte having a common ion is called common ion effect.

Option D is correct.