Question

In a buffer solution consisting of a weak acid and its salt, the ratio of concentration of salt to acid is increased tenfold, then the $pH$ of the solution will:

• A. Increase by one
• B. Increase tenfold
• C. Decrease by one
• D. Decrease tenfold

Answer 1

The correct option is A Increase by one

Using Henderson's equation,
$pH=p{K}_a+\log \frac{\left[\text{Salt}\right]}{\left[\text{Acid}\right]}$
According to the question, ratio of the concentration of salt to acid is increased tenfold.
Hence,
$pH=p{K}_a+\log \frac{10\left[\text{Salt}\right]}{\left[\text{Acid}\right]}$
$pH=\log 10+\log \frac{\left[\text{Salt}\right]}{\left[\text{Acid}\right]}+p{K}_a$
$pH=1+\log \frac{\left[\text{Salt}\right]}{\left[\text{Acid}\right]}+p{K}_a$
The $pH$ of the solution will increase by $1$.