Question

When the following is added to 20 ml of 0.1 M $C{H}_{3}COOH$ +20 ml of $C{H}_{3}COONa$. The pH of the solution does not change:

• A. 10 ml of 0.1 M $C{H}_{3}COOH$.
• B. 10 ml of 0.1 M $C{H}_{3}COONa$.
• C. 10ml of water
• D. 20 ml of 0.2 M $C{H}_{3}COOH$

Answer 1

The correct option is C 10ml of water

A mixture of acetic acid and sodium acetate is a acidic buffer. Its aqueous solution is acidic in nature.
The expression for the pH of the acidic buffer solution is as given below.
$pH=p{K}_a+log\frac{\left[salt\right]}{\left[acid\right]}$
When 10 ml of water is added to the mixture containing 20 ml of 0.1 M $C{H}_{3}COOH$ +20 ml of $C{H}_{3}COONa$, the $p{K}_a$ of acetic acid is unaffected. Also the ratio $\frac{\left[salt\right]}{\left[acid\right]}$ is unaffected. Hence the pH of solution remains unchanged.