Question

What happens to the pH of a buffer system if one halves the concentration of both the acid and the salt?

• A. Nothing happens
• B. pH goes up because there is less total acid in the solution.
• C. pH goes down because there is less conjugate base to mask the presence of the
• D. It depends upon the original concentration of acid and salt.
• E. It is impossible to predict.

Answer 1

The correct option is A Nothing happens

For an acid buffer,

$pH=p{k}_a+\log \frac{\left[salt\right]}{\left[acid\right]}$

When concentrations of both the salt and acid are halved, the ratio $\frac{\left[salt\right]}{\left[acid\right]}$ still remains the same and hence $pH$ does not change and it remains the same.