Q19.2P - Chemistry: Molecular Nature Of Matter And Change

Question

How do the acid and base components of a buffer function? Why are they often a conjugate acid-base pair of a weak acid?

Step-by-Step Solution

Answer

The acidic component of the buffer reacts with ions of added base, while the basic component reacts with ions of added acid, reducing the effect of added bases or acids to a slight ph shift.

Because its components cannot neutralise each other, buffers are frequently a conjugate acid-base pair of a weak acid.

Step 1: Acidic buffer solution

An acidic buffer solution is formed by mixing a weak acid with the salt having its conjugate base.

Step 2: Basic buffer solution

A basic buffer solution is the one which is formed by combining a weak base with a salt solution of its conjugate acid.

Step 3: Function of a buffer

For example, consider an acidic buffer:

${\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{CH}}_3\mathrm{COONa}$

When a strong acid HCl is added, then the salt ${\mathrm{CH}}_3\mathrm{COONa}$ reacts with it and nullifies the change in pH as shown:

${\mathrm{CH}}_3\mathrm{COONa}+\mathrm{HCl}\to {\mathrm{CH}}_3\mathrm{COOH}+\mathrm{NaCl}$

So, the weak ${\mathrm{CH}}_3\mathrm{COOH}$ acid is formed.

When a strong base NaOH is added, then the weak acid ${\mathrm{CH}}_3\mathrm{COOH}$ reacts with it and nullifies the change in pH as shown:

${\mathrm{CH}}_3\mathrm{COOH}+\mathrm{NaOH}\to {\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{H}}_2\mathrm{O}$

So, the weak acid ${\mathrm{CH}}_3\mathrm{COOH}$ is formed again. Like this the pH of the entire solutions remains unchanged on adding either strong acid or a strong base.