Chapter 19, Problem 19.20P

Interpretation Introduction

Interpretation:

The $\text{pH}$ of the given buffer solution prepared by mixing 0.25 M ${\text{NH}}_{\text{3}}$ and 0.15 M ${\text{NH}}_{\text{4}}\text{Cl}$ has to be calculated.

Concept Introduction:

Henderson-Hasselbalch equation:

The $\text{pH}$ at an intermediate stage of the titration is calculated by using the following equation,

$\begin{array}{l}\text{pH}\text{=}{\text{pK}}_{\text{a}}\text{+}\text{log}\frac{\left[\text{base}\right]}{\left[\text{acid}\right]}\\ \text{where,}\\ \text{pH}\text{=}\text{-}\text{log}\left[{\text{H}}^{\text{+}}\right]\\ {\text{pK}}_{\text{a}}\text{=}\text{-}\text{log}{\text{K}}_{\text{a}}\left({\text{K}}_{\text{a}}\text{-}\text{acid}\text{dissociation}\text{constant}\right)\end{array}$

This equation is known as Henderson-Hasselbalch equation.