Question

If a small amount of a strong base is added to a buffer made up of a weak acid, HA, and the sodium salt of its conjugate base, NaA, the pH of the buffer solution does not change appreciably because

A.CH₃COOK or NaOH

B.CH₃COOK only

C.NaOH only

D.NH₄Cl only

E.NaCl or CH₃COOK

Answer 1

Buffer solution is a solution which resists the change in pH.

Buffer solutions are two types.

1. Acidic buffer

2. Basic buffer

Acidic buffer: It is a mixture of weak acid and salt formed by this weak acid with a strong base.

Ex: Acetic acid (CH₃COOH) + Sodium acetate (CH₃COONa).

Sodium acetate is a salt of acetic acid (weak acid) and sodium hydroxide (strong base)

Basic buffer: It is a mixture of weak base and salt formed by this weak base with a strong acid.

Ex: Ammonium hydroxide (NH₄OH) + ammonium chloride (NH₄Cl). Ammonium chloride is a salt of Ammonium hydroxide (weak base) and HCl ( strong acid)

When a strong base is added to buffer, pH does not change appreciably. It is due to

In the buffer the following reactions exists.

When NaOH is added to the buffer, hydroxide ions(OH^​​​- ) from base, reacts with Hydronium ions from acetic acid. Hence the equilibrium exists in acetic acid shifts towards right ie dissociation of acetic acid increases. The hydroxide ions are removed from the system. The effect hydroxide ions is suppressed. Hence pH does not change appreciably.

pH is not changed much due to formation of acetate or potassium acetate only.

Option B is correct.