Question

Which among the following salts undergoes hydrolysis?

• A. $\text{Na}_2\text{SO}_4$
• B. KCl
• C. $\text{NH}_4\text{Cl}$
• D. $\text{KNO}_3$

Hint:

To spot a hydrolyzable salt instantly, look for the presence of a "weak" partner component in the formula. If you see ions like $\text{NH}_4^+$, $\text{CH}_3\text{COO}^-$, or $\text{CN}^-$, it will definitely undergo hydrolysis!

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The problem asks us to determine which of the listed chemical salts will undergo salt hydrolysis when dissolved in water.

Step 2: Key Formula or Approach:
Salt hydrolysis is a process in which the constituent cations or anions of a salt react with water to alter the pH.
Salts derived from a strong acid and a strong base do not undergo hydrolysis; their ions are spectator ions and the solution remains neutral.
Salts containing a conjugate ion from a weak acid or a weak base will actively undergo hydrolysis.

Step 3: Detailed Explanation:
Let's break down the acid-base parentage of each option:
(A) $\text{Na}_2\text{SO}_4$: Formed from a strong base (NaOH) and a strong acid ($\text{H}_2\text{SO}_4$). Its ions do not react with water.
(B) KCl: Formed from a strong base (KOH) and a strong acid (HCl). It does not undergo hydrolysis.
(C) $\text{NH}_4\text{Cl}$: Formed from a weak base ($\text{NH}_4\text{OH}$) and a strong acid (HCl). The ammonium ion ($\text{NH}_4^+$) is a relatively strong conjugate acid and will react with water molecules:
$$\text{NH}_4^+ + \text{H}_2\text{O} \rightleftharpoons \text{NH}_4\text{OH} + \text{H}^+$$ Because it reacts with water, it undergoes cationic hydrolysis, making the solution acidic.
(D) $\text{KNO}_3$: Formed from a strong base (KOH) and a strong acid ($\text{HNO}_3$). It does not undergo hydrolysis.

Step 4: Final Answer:
The salt that undergoes hydrolysis is $\text{NH}_4\text{Cl}$, matching option (C).