Chapter 19, Problem 19.39P

Interpretation Introduction

Interpretation:

The buffer component concentration ratio $\left[{\text{HPO}}_{\text{4}}^{\text{2-}}\right]\text{/}\left[{\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{\text{-}}\right]$ has to be calculated for the oxoanions of phosphorus.

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.

Buffer-component concentration ratio:

Buffer-component concentration ratio is given by,

$\text{Buffer-component concentration ratio}\text{=}\frac{\text{concentration}\text{of}\text{base}\text{in}\text{buffer}}{\text{concentration}\text{of}\text{acid}\text{in}\text{buffer}}$

When the buffer-component concentration ratio is equal to 1, the buffer resists changes in $\text{pH}$ with added acid to the same extent that it resists changes in $\text{pH}$ with added base.