Question

Which among the following salts is NOT hydrolysed in water?

• A. \(\text{Na}_2\text{CO}_3\)
• B. \(\text{NH}_4\text{CN}\)
• C. \(\text{KNO}_3\)
• D. \(\text{KCN}\)

Hint:

Strong acid + strong base salt → neutral solution → no hydrolysis.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Salt hydrolysis occurs when ions of a salt react with water to form acidic or basic solutions. Salts of strong acids and strong bases do not undergo hydrolysis because their constituent ions (\(\text{Na}^+, \text{K}^+, \text{Cl}^-, \text{NO}_3^-\), etc.) are very weak conjugate species and do not interact significantly with water.
Step 2: Key Formula or Approach:
Identify the parent acid and base for each salt:
- \(\text{Na}_2\text{CO}_3\): \(\text{NaOH}\) (SB) + \(\text{H}_2\text{CO}_3\) (WA) \(\rightarrow\) Hydrolysed (anionic).
- \(\text{NH}_4\text{CN}\): \(\text{NH}_4\text{OH}\) (WB) + \(\text{HCN}\) (WA) \(\rightarrow\) Hydrolysed (both).
- \(\text{KNO}_3\): \(\text{KOH}\) (SB) + \(\text{HNO}_3\) (SA) \(\rightarrow\) No hydrolysis.
- \(\text{KCN}\): \(\text{KOH}\) (SB) + \(\text{HCN}\) (WA) \(\rightarrow\) Hydrolysed (anionic).
Step 3: Detailed Explanation:
\(\text{KNO}_3\) is derived from Potassium Hydroxide (a strong base) and Nitric Acid (a strong acid). In aqueous solution, it dissociates completely into \(\text{K}^+\) and \(\text{NO}_3^-\). Neither ion reacts with water to produce excess \(\text{H}^+\) or \(\text{OH}^-\) ions. The solution remains neutral.
Step 4: Final Answer:
\(\text{KNO}_3\) is not hydrolysed.