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. 5.21

Answer 1

The correct option is B 4.76

$\text{mole of sodium acetate}=20\times 0.5=10$
$\text{mole of acetic acid}=10\times 1=10$
total volume after dilution = 100+20+10=130 ml
$\left[\text{sodium acetate}\right]=\frac{10}{130}$
$\left[\text{acetic acid}\right]=\frac{10}{130}$
using Henderson Equation.
$pH=p{K}_a+\log \frac{\left[salt\right]}{\left[acid\right]}$
$pH=4.76+\log \left(\frac{\frac{10}{130}}{\frac{10}{130}}\right)$
$pH=4.76+\log \left(\frac{10}{10}\right)$
$pH=4.76$