Question

A salt of strong acid and a weak base is dissolved in water. Its hydrolysis in solution is?
(A) Unaffected on heating
(B) Increased by adding a strong acid
(C) suppressed by diluting
(D) suppressed by adding a strong acid

Answer 1

Hint: the hydrolysis of salt causes the solution to become either acidic or basic depending on the cation and anion of the salt which gives either ${{H}^{+}}$ or $O{{H}^{-}}$ in water, thus degerming its acidity and basicity.

Complete step by step solution:
A salt is formed by the reaction of an acid and base. This is called the neutralisation reaction which produces salt and water. Taking an example of a strong acid such as hydrochloric acid, $HCl$ and a weak base like ammonium hydroxide, $N{{H}_{4}}OH$. On reacting it produces ammonium salt, $N{{H}_{4}}Cl$ and water. The reaction is as follows:
\[HCl+N{{H}_{4}}OH\to N{{H}_{4}}Cl+{{H}_{2}}O\]
This salt on dissolving in the water breaks down completely into its constituent ions with water. Thus, acting as an electrolyte and making the solution either acidic or basic depending on the reactivity of the ions which now act as acid or base as they produce either ${{H}^{+}}\,or\, O{{H}^{-}}$ ions with water.
In the case of, the strong acid and weak base salt reacting with water, which is the reverse process of the neutralisation reaction is known as hydrolysis. The cation $N{{H}_{4}}^{+}$of the salt is the conjugate acid or a weak base (ammonium hydroxide) and is capable of giving an electron in water, thus acting as an acid.
Whereas, $C{{l}^{-}}$ acts as a spectator and is a conjugate base of a strong acid (hydrochloric acid).
Thus, the hydrolysis of salt is as follows: $NH_{4}^{+}(aq)+{{H}_{2}}O(aq)\rightleftarrows {{H}_{3}}{{O}^{+}}(aq)+N{{H}_{3}}(aq)$
Therefore, the salt solution is acidic, with a pH of less than 7. But by making the acid stronger, it will cause the reaction to shift on the right side (that is, neutralisation reaction)

Thus, option (D)- suppress the hydrolysis process on adding strong acid.

Note: The water being a weak electrolyte is neutral with pH equal to 7, having equal concentration $\left[ {{H}^{+}} \right]=\left[ O{{H}^{-}} \right]$. The hydrolysis of salt causes the pH of the solution to deter from 7 as it shows acidic or basic nature accordingly.