Question

The pH of resultant solution of 20 mL of 0.1 M $\text{CH}_{\text{3}} \text{COOH}$ and 20 mL of 0.1 M $\text{CH}_{\text{3}} \text{COONa}$ is

• A. $pK_{a_{1}}$
• B. $pK_{a_{2}}$
• C. $\frac{p K_{a_{1}} + p K_{a_{2}}}{2}$
• D. 2

Answer 1

Answer: (B)

$\left[\text{CH}_{\text{3}} \text{COOH}\right] \text{=} \left[\text{CH}_{\text{3}} \text{COONa}\right]$
The resultant solution will be a buffer solution.
So $pH=pK_{a_{2}}+log\left[\frac{CH_{3} - COOH}{CH_{3} - COONa}\right]$ …(ii)
From (i) and (ii)
$pH=pK_{a_{2}}$ .