Question

Which among the following salt turns blue litmus red in its aqueous solution?

• A. $\text{CuSO}_{4}$
• B. $\text{Na}_{2}\text{CO}_{3}$
• C. $\text{Na}_{2}\text{SO}_{4}$
• D. $\text{NaNO}_{3}$

Hint:

Hydrolysis Cheat Sheet:
Strong Acid + Strong Base $\rightarrow$ Neutral (No color change).
Weak Acid + Strong Base $\rightarrow$ Basic (Red litmus to Blue).
Strong Acid + Weak Base $\rightarrow$ Acidic (Blue litmus to Red).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Turning blue litmus red means the solution is acidic. This happens when a salt is formed from a Strong Acid and a Weak Base.

Step 2: Formula Application:
1. $Na_2SO_4$: Strong Base ($NaOH$) + Strong Acid ($H_2SO_4$) = Neutral. 2. $Na_2CO_3$: Strong Base ($NaOH$) + Weak Acid ($H_2CO_3$) = Basic. 3. $CuSO_4$: Weak Base ($Cu(OH)_2$) + Strong Acid ($H_2SO_4$) = Acidic.

Step 3: Explanation:
In water, $CuSO_4$ undergoes salt hydrolysis. The $Cu^{2+}$ ion reacts with water to produce $H^+$ ions, making the solution acidic. $Cu^{2+} + 2H_2O \rightleftharpoons Cu(OH)_2 + 2H^+$.

Step 4: Final Answer:
$CuSO_4$ turns blue litmus red.