Question

Explain Mechanism or working of acid buffer.

Answer 1

Consider acidic buffer mixture,

CH₃COOH ⇌ CH₃COO^– + H⁺;

CH₃COONa → CH₃COO^– + Na⁺

Here, acetic acid is a weak electrolyte, in it’s solution there exists equilibrium between it’s ions and molecules. Where as sodium acetate completely dissociates into it’s ions.

Therefore, the buffer mixture contains large number of CH₃COO^– ions followed by Na⁺ , H⁺ , CH₃COOH.

Case i) When an acid added to this solution:

H⁺ ion of the acid combines with CH₃COO^– ion in buffer solution and makes equilibrium with acetic acid.

CH₃COO^– + H⁺ ⇌ CH₃COOH

As a result pH remains constant.

Case ii) When a base is added to this solution:

OH^– ion of the base combines with H⁺ ion in buffer solution forms water molecule.

H⁺ + OH^– → H₂O

As a result pH remains constant.