Question

Assertion : The $pH$ of an aqueous solution of acetic acid remains unchanged on addition of sodium acetate.
Reason : The ionization of acetic acid is increased by addition of sodium acetate.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (D)

Addition of a small amount of $CH_3COONa$ to acetic acid increases the pH value because $CH_3COONa$ is a strong electrolyte and thus ionizes to give $CH_3COO^-$ and $Na^+$ ions. Due to common ion effect, it suppresses the ionization of $CH_3COOH$ which decreases $[H^+]$ and hence $pH$ value increases.