Question

Assertion :On addition of ${NH}_{4}Cl$ to ${NH}_{4}OH$ solution, $pH$ decreases but remains greater than $7$. Reason: Addition of ${NH}_4^{+}$ ion decreases ionisation of ${NH}_{4}OH$ thus $\left[{OH}^{-}\right]$ is decreased hence, $pH$ decreases.

• 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. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

The solubility of a sparingly soluble salt is reduced in a solution that contains an ion in common with that salt. $N{H}_{4}OH$ is a weak base and $N{H}_4^{+}$ is the common ion in $N{H}_{4}OH$ and $N{H}_{4}Cl$. Due to this common ion, the dissociation of $N{H}_{4}OH$ decreases.

Due to common ion effect ionisation of ${NH}_{4}OH$ decreases so $pH$ decreases.