Chapter 9, Problem 9.32P

Interpretation Introduction

Interpretation:

The explanation has to be given why the buffer capacity reaches a maximum limit when ${\text{pH=pK}}_{\text{a}}$ .

Concept Introduction:

The measure of capability of a solution to resist the $\text{pH}$ changes either by absorbing ${\text{H}}^{\text{+}}\text{and}{\text{OH}}^{\text{-}}$ ions or by desorbing the ${\text{H}}^{\text{+}}\text{and}{\text{OH}}^{\text{-}}$ ions. The effect of $\text{pH}$ in buffer can be seen upon the addition of base or acid to the buffer system. The effect of $\text{pH}$ in buffer depends on both the initial $\text{pH}$ and the capability of the buffer to resist the $\text{pH}$ change

The number of moles of acid or base that is necessary to change the $\text{pH}$ by 1 and then divided by the change in $\text{pH}$ along with volume of buffer is called as buffer capacity.

It is given by the formula,

$\text{β=}\frac{{\text{dC}}_{\text{b}}}{\text{dpH}}\text{=}\frac{{\text{dC}}_{\text{a}}}{\text{dpH}}$

Here, ${\text{C}}_{\text{a}}\text{and}{\text{C}}_{\text{b}}$ = moles of strong acid and base per litre that is required to produce a change in $\text{pH}$ by one.

To explain why the buffer capacity reaches a maximum limit when ${\text{pH=pK}}_{\text{a}}$