Question

When \[N{{H}_{4}}Cl~\]is added to \[N{{H}_{4}}OH~\] solution, the dissociation of ammonium hydroxide is reduced. It is due to:
(A) Common ion effect
(B) Hydrolysis
(C) Oxidation
(D) Reduction

Answer 1

Hint: Given solvent is ammonium hydroxide, \[N{{H}_{4}}OH~\]. Ammonium hydroxide is the base because ammonium hydroxide is aqueous ammonia, which means the ammonia solution contains two ions \[N{{H}_{4}}^{+}\] and \[O{{H}^{-}}\]. As it contains hydroxyl ion so as per Arrhenius’s concept regarding base (a substance which can easily release hydroxyl ion is base), ammonium hydroxide is base.

Complete Step by Step Solution:
When \[N{{H}_{4}}Cl~\] is added to aqueous ammonia, then ammonium chloride dissociates to give ions\[(N{{H}_{4}}^{+}and\text{ }C{{l}^{-}})\] because it is a salt and also a strong electrolyte (dissociates into ions after dissolving in water) such as
\[N{{H}_{4}}Cl\rightleftarrows N{{H}_{4}}^{+}+\text{ }C{{l}^{-}}\]

Solvent (ammonium hydroxide) which itself contains ammonia \[\left( N{{H}_{3}} \right)\], ammonium caution \[\left( N{{H}_{4}}^{+} \right)\], hydroxyl anion \[\left( O{{H}^{-}} \right)\]and \[N{{H}_{4}}Cl~\] will also give ammonium caution \[\left( N{{H}_{4}}^{+} \right)\]when added to ammonium hydroxide. Due to this concentration of ammonium anion increases in the solution and thus equilibrium shifts towards the left.

In other words, ammonium hydroxide which is a weak electrolyte so dissociates into ion difficulty but adding further ammonium chloride which is a strong electrolyte (dissociates into ions easily) reduces the dissociation of ammonium hydroxide due to the common ion effect of ammonium caution \[\left( N{{H}_{4}}^{+} \right)\].
Thus, the correct option is A.

Note: It is important to note that the solution of ammonium chloride (strong electrolyte) and ammonium hydroxide (weak electrolyte) form a buffer solution. Buffer solution does not allow the change in the pH of the solution if adding acid or base even in a small amount or if the concentration of acid or base increases or decreases anyhow.