Question

Which of the following cannot be hydrolyzed?
A. A salt of a weak acid and strong base.
B. A salt of strong acid and weak base.
C. A salt of a weak acid and weak base.
D. A salt of strong acid and a strong base.

Answer 1

Hint: Salt hydrolysis is a reaction that one of the ions of a salt reacts with ${{H}_{2}}O$, producing either a basic or acidic solution that will affect ${{p}^{H}}$ the solution. All the salts undergo hydrolysis reaction in an aqueous solution except neutral salt like NaCl.

Complete step by step solution:
Salts can be classified based on hydrolysis into three main categories: neutral salts, acidic salts, and basic salts respectively.
a. Neutral salts: Neutral salts are formed by the neutralisation of strong acids and strong bases. Neutral salts do not undergo hydrolysis reaction because cations and anions form a strong electrostatic bond, and can not be broken easily. Instead of hydrolysis, they can only get hydrated. For example, NaCl is a neutral salt, formed by strong acid, HCl, and a strong base, NaOH can not be hydrolyzed.

b. Acidic salts: Acidic salts are formed by the neutralisation of strong acids and weak bases. This type of salt undergoes hydrolysis. For example: $N{{H}_{4}}Cl$, is formed by strong acid HCl and a weak base $N{{H}_{4}}OH$.
$N{{H}_{4}}Cl(aq.)\rightleftharpoons NH_{4}^{+}(aq.)+C{{l}^{-}}(aq.)$
$NH_{4}^{+}(aq.)+{{H}_{2}}O(aq.)\rightleftharpoons N{{H}_{4}}OH(aq.)$

c. Basic salts: Basic salts are formed by the neutralisation of weak acids and strong bases. Basic salts like $C{{H}_{3}}COONa$are formed by weak acid $C{{H}_{3}}COOH$and a strong base $NaOH$undergoes hydrolysis.
$C{{H}_{3}}COONa(aq.)\rightleftharpoons C{{H}_{3}}CO{{O}^{\_}}(aq.)+N{{a}^{+}}(aq.)$
$C{{H}_{3}}CO{{O}^{-}}(aq.)+{{H}_{2}}O(aq.)\rightleftharpoons C{{H}_{3}}COOH(aq.)$

There is also another type of salts of weak acids and weak bases whose nature can either be acidic or basic depending upon the acids and bases involved. For example $C{{H}_{3}}COON{{H}_{4}}$, is formed by weak acid $C{{H}_{3}}COOH$and weak base $N{{H}_{4}}OH$.
$C{{H}_{3}}COON{{H}_{4}}(aq.)\rightleftharpoons C{{H}_{3}}CO{{O}^{-}}(aq.)+NH_{4}^{+}(aq.)$
$C{{H}_{3}}CO{{O}^{-}}(aq.)+NH_{4}^{+}(aq.)+{{H}_{2}}O(aq.)\rightleftharpoons C{{H}_{3}}COOH(aq.)+N{{H}_{4}}OH(aq.)$
Therefore, salts of strong acid and strong base can not be hydrolyzed.
Thus, Option (D) is correct.

Note: The ${{p}^{H}}$ of any salt solution depends on whether and to what extent their ions, which are conjugate bases or acids, react with the aqueous solution and hydrolyze it, releasing ${{H}^{+}}$ or $O{{H}^{-}}$ ions. The stronger the acid or base, the weaker the conjugates and , vice versa.