Chapter 19, Problem 19.13P

Interpretation Introduction

Interpretation:

The $\left[{\text{H}}_3{\text{O}}^{+}\right]$ and the $\text{pH}$ of a benzoic acid-benzoate buffer is to be determined which consist of $0.33M{\text{ C}}_{\text{6}}{\text{H}}_{\text{5}}\text{COOH}$ and $0.28M{\text{C}}_{\text{6}}{\text{H}}_{\text{5}}\text{COONa}$.

Concept introduction:

Buffer solutions are the solutions that resist any change in $\text{pH}$ whenever any small amount of acid or alkali are added to it. There are two types of buffer solutions which are as follows:

1. Acidic Buffer- The buffer solutions which are consist of weak acid andits conjugate base with $\text{pH}$ less than 7 are known as acidic buffer.

For example: ${\text{CH}}_{\text{3}}\text{COOH}-{\text{CH}}_{\text{3}}\text{COONa}$ buffer.

2. Basic Buffer- The buffer solutions which are consist of weak base andits conjugate acid with $\text{pH}$ greater than 7 are known as basic buffer. For example: ${\text{NH}}_{\text{4}}\text{OH}-{\text{NH}}_{\text{4}}\text{Cl}$ buffer.

The $\text{pH}$ of a buffer solution is given by Henderson- Hasselbalch equation which relates the $\text{pH}$ with concentration of acid $\left[\text{HA}\right]$ and concentration of conjugate base $\left[{\text{A}}^{-}\right]$ as follows,

$\text{pH}=\text{p}{K}_{\text{a}}+\log \frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$ (1)

The relation between $\text{p}{K}_{\text{a}}$ and $K_{\text{a}}$ is as follows,

$\text{p}{K}_{\text{a}}=-\log K_{\text{a}}$ (2)

The relation between $\text{pH}$ and $\left[{\text{H}}_3{\text{O}}^{+}\right]$ is as follows,

$\text{pH}=-\log \left[{\text{H}}_{\text{3}}{\text{O}}^{+}\right]$ (3)