Question

The ratio of volumes of $C{H}_{3}COOH$ $\left(0.1N\right)$ to $C{H}_{3}COONa$ $\left(0.1N\right)$ required to prepare a buffer solution of $pH$ 5.74 is:

(Given $p{K}_a$ of $C{H}_{3}COOH$ is 4.74)

• A. 10 : 1
• B. 5 : 1
• C. 1 : 5
• D. 1 : 10

Answer 1

Answer: (D)

1 : 10

Let the volumes of acetic acid and sodium acetate be V L and V' L respectively.

$pH=pKa+log\frac{\left[C{H}_{3}COONa\right]}{\left[C{H}_{3}COOH\right]}$

$5.74=4.74+log\frac{0.1\times V^{\prime }}{0.1\times V}$

$1=log\frac{V^{\prime }}{V}$

$\frac{V^{\prime }}{V}=10$

$\frac{V}{V^{\prime }}=1:10$