Question

Which of the following aqueous mixture is a buffer solution?

• A. Acetic acid + Ammonium chloride
• B. Hydrochloric acid + Potassium acetate
• C. Acetic acid + Sodium chloride
• D. Acetic acid + Sodium acetate
• E. Sodium hydroxide + Potassium acetate

Hint:

Buffer solutions are created by mixing a weak acid with its conjugate base (or a weak base with its conjugate acid). In this case, acetic acid and sodium acetate form a buffer system.

Answer 1

The Correct Option is D

A buffer solution consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in equilibrium. The purpose of the buffer is to maintain a relatively constant pH even when small amounts of an acid or base are added to the solution.
In this case, acetic acid is a weak acid and sodium acetate is the salt of the conjugate base of acetic acid (\( {CH}_3{COO}^- \)).
The mixture of acetic acid and sodium acetate forms a buffer solution because the acetic acid dissociates to produce \( {H}^+ \) and \( {CH}_3{COO}^- \), and the sodium acetate dissociates to produce \( {CH}_3{COO}^- \) and \( {Na}^+ \), thus maintaining the pH of the solution.
Therefore, the correct answer is (D) Acetic acid + Sodium acetate.