Question

Assertion: The pH of an aqueous solution of $C{H}_{3}COOH$ remains unchanged on the addition of $C{H}_{3}COONa$.
Reason: The ionisation of $C{H}_{3}COOH$ is supressed by the addition of $C{H}_{3}COONa$.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct
• E. Both Assertion and Reason are incorrect

Answer 1

The correct option is D Assertion is incorrect but Reason is correct

Adding a common ion prevents the weak acid or weak base from ionizing as much as it would without the added common ion. The common ion effect suppresses the ionization of a weak acid by adding more of an ion that is a product of this equilibrium.

So addition of $C{H}_{3}COONa$ to $C{H}_{3}COOH$ increases the pH of solution but addition of $N{H}_{4}Cl$ to $N{H}_{4}OH$ decreases the pH of solution.