Question

A buffer solution is prepared by mixing 10 ml of 1.0 M acetic acid and 20 ml of 0.5 M sodium acetate and then diluted to 100 ml with distilled water. If the $p{K}_a$ of $C{H}_{3}COOH$ is 4.76, what is the pH of the buffer solution prepared?

• A. 5.21
• B. 4.76
• C. 4.34
• D. 2.52

Answer 1

The correct option is B 4.76

Given, $\left[C{H}_{3}COOH\right]=1.0M,\left[C{H}_{3}COONa\right]=0.5M$
volume of acetic acid = 10 ml
volume of sodium acetate = 20 ml
volume of distilled water = 100 ml
Apply Henderson equation :
$pH=p{K}_a+log\frac{\left[Salt\right]}{\left[Acid\right]}$
$pH=p{K}_a+log\frac{\left[C{H}_{3}COONa\right]}{\left[C{H}_{3}COOH\right]}$
$pH=4.76+log\left(\frac{20\times 0.5}{10}\right)$
$pH=4.76$