Question

The $K_a$ of propionic add is $1.34\times 10-5$. What is the $pH$ of a solution containing $0.5$ M propionic acid and $0.5$ M sodium propionate?

Answer 1

As we know that,

$p_{K_a}=-\log K_a$

$\because K_a=1.34\times {10}^{-5}\left(\text{Given}\right)$

$\therefore p{K}_a=-\log (1.34\times {10}^{-5})$

$\Rightarrow p{K}_a=5-0.127=4.873$

Now,

$pH=p{K}_a+\log \left(\frac{\left[\text{salt}\right]}{\left[\text{acid}\right]}\right)$

Given:-

$\left[\text{salt}\right]=\left[\text{acid}\right]=0.5M$

$\therefore pH=4.87+\log \frac{0.5}{0.5}=4.873$

Hence the pH of the solution is $4.873$.