Chapter 3, Problem 27RQ

Summary Introduction

Interpretation:

The pH of a solution prepared by mixing $300\text{ mL}$ of $0.25\text{ M}$ sodium hydrogen ascorbateand $\text{150 mL}$ of $0.2\text{ M}$ HCl is to be calculated.

Concept introduction:

The pH is the precise measure of the acidity or basicity of a particular solution. It can be calculated as the negative logarithm of H⁺ (hydrogen ion) concentration.

The Henderson–Hasselbalch expression for a weak acid and its conjugate base is as follows:

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

Here, pH is the measure of the acidity of the solution, $\text{p}{K}_{\text{a}}$ 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.

The buffer is the combination of weak acid with its conjugate base or a weak base with its conjugate acid. The pH of the buffer solution does not change very much when the strong acid or base added to the buffer solution.