Chapter 3, Problem 30RQ

Summary Introduction

Interpretation:

The pH of the mixture of onemole of benzoic acid with onemole of sodium benzoate is to be calculated.

Concept introduction:

The pH of the mixture of weak acid and its conjugate base or a weak base with its conjugate acid is calculated by the use of Henderson–Hasselbalch equation. The Henderson–Hasselbalchequation for a weak acid and its conjugate base is:

$\text{pH}={\text{pK}}_{\text{a}}+\log \frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$

Here, pH is the measure of the acidity of the solution, $\text{p}{K}_a$ is the negative logarithm of the dissociation constant, $\left[\text{HA}\right]$ is the concentration of weak acid, and $\left[{\text{A}}^{-}\right]$ is the concentration of its conjugate base.