Which of the following solutions is slightly acidic due to hydrolysis?

Question

Question

This question was previously asked in

RRB NTPC Graduate Level CBT-I Official Paper (Held On: 05 Jun, 2025 Shift 1)

Answer 1

The correct answer is NH₄Cl.

Key Points

NH₄Cl (Ammonium chloride) is a salt of a weak base (NH₃) and a strong acid (HCl), making its aqueous solution slightly acidic due to hydrolysis.
In water, NH₄Cl dissociates into NH₄⁺ and Cl⁻ ions. The NH₄⁺ ion undergoes hydrolysis to form NH₃ and H⁺ ions, increasing the acidity.
The Cl⁻ ion does not hydrolyze because it is the conjugate base of a strong acid (HCl) and remains inert in the solution.
The pH of an NH₄Cl solution is typically less than 7, confirming its acidic nature.
Other options like Na₂CO₃ and CH₃COONa are basic, while NH₄CH₃COO is nearly neutral due to the balance between its acidic and basic components.

Additional Information

Hydrolysis: It is the reaction of a salt with water to form an acidic or basic solution depending on the strength of the parent acid and base.
Ammonium Ion (NH₄⁺): It is a weak acid that hydrolyzes in water, releasing H⁺ ions and contributing to the solution's acidity.
Conjugate Acid-Base Pair: NH₄⁺ is the conjugate acid of the weak base NH₃, while Cl⁻ is the conjugate base of the strong acid HCl.
pH of Salts: The pH of a salt solution depends on the hydrolysis of its ions. Salts of strong acids and weak bases are acidic, while salts of strong bases and weak acids are basic.
Non-Hydrolyzing Ions: Ions like Cl⁻, derived from strong acids, do not hydrolyze and do not affect the solution's pH.