Calculate the pH of a buffer containing 0.182 M HNO2 and 0.170 M NaNO2 at 25°C. The pKa value for HNO2 is 3.40.

Question

An acid–base buffer is a solution that resists changes in pH when a small amount of strong acid or base is added. Acid–base buffers typically contain a weak acid and its conjugate base.

Answer 1

The equation we generally use to calculate the pH of an acidic buffer is the Henderson Hasselbalch equation:

pH = pKa + log [conj.base] / [acid]

Plug the given information into this equation and solve for pH...

pH = 3.40 + log [0.170] / [0.183]

pH = 3.40 + log 0.929

pH = 3.40 - 0.032

pH = 3.37