Question

Aqueous solution sof $H{NO}_3,KOH,{CH}_{3}COOH,{CH}_{3}COONa$ of identical concentrations are provided. The pairs of solution swhich forms a buffer upon mixing is (are):

• A. $H{NO}_3$ and ${CH}_{3}COOH$
• B. $KOH+{CH}_{3}COONa$
• C. $H{NO}_3$ and ${CH}_{3}COONa$
• D. ${CH}_{3}COOH+{CH}_{3}COONa$

Answer 1

Answer: (C), (D)

The correct options are
C $H{NO}_3$ and ${CH}_{3}COONa$
D ${CH}_{3}COOH+{CH}_{3}COONa$

Following are the types of Buffer Solutions:
1. Acidic Buffer: Weak Acid + its Salt of Strong Base
2. Basic Buffer: Weak Base + its Salt of Strong Acid
3. Neutral Buffer: Salt of Weak Acid and Weak Base (rarely used)
Option A has a mixture of $HN{O}_3$ (Strong Acid) and $C{H}_{3}COOH$ (Weak Acid). Hence, it is not a Buffer solution.
Option B has a mixture of $KOH$ (Strong Base) and $C{H}_{3}COONa$ (Salt of Weak Acid and Strong Base). Hence, it is not a Buffer solution.
Option D has a mixture of $C{H}_{3}COOH$ (Weak Acid) and $C{H}_{3}COONa$ (its Salt with a Strong Base). Hence, it is a Buffer solution.
Option C has a mixture of $HN{O}_3$ (Strong Acid) and $C{H}_{3}COONa$ (its Salt with a Strong Base). Hence, it can act as a Buffer solution in the following case:
When Moles of $C{H}_{3}COONa$ initially present is greater than the moles of $HN{O}_3$ present in the mixture. This is because, following reaction would take place in the mixture:
$HN{O}_3+C{H}_{3}COONa\to C{H}_{3}COOH+NaN{O}_3$
We know that a mixture of $C{H}_{3}COOH$ and $C{H}_{3}COONa$ is a Buffer Solution which can only be formed when some of the $C{H}_{3}COONa$ remains unreacted i.e. when $C{H}_{3}COONa$ is taken in an excess.

Hence,option C and D are correct.