Question

Assertion :For the analysis of $II{I}^{rd}$ group basic radicals, $N{H}_{4}Cl$ is added to suppress the ionisation of $N{H}_{4}OH$. Reason: With high concentration of $O{H}^{-}$ ions, basic radicals of other groups also get precipitated with $II{I}^{rd}$ group basic radicals.

• 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 incorrect but Reason is correct
• D. Assertion is correct but Reason is incorrect

Answer 1

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

During salt analysis of third group radicals, $N{H}_{4}Cl$ is added to suppress the ionisation of $N{H}_{4}OH$ because $N{H}_{4}Cl$ is a strong electrolyte and it decomposes completely. While the $N{H}_{4}OH$ is a weak base which does not ionises completely. Thus, due to presence of $N{H}_4^{+}$ in $N{H}_{4}Cl$ suppresses the ionisation of weak base $N{H}_{4}OH$. In order to decrease the $O{H}^{-}$ concentration, it is sufficient to precipitate the cations of third group as their hydroxide (having low $Ksp$ values) prevents the precipitation of basic radicals of other groups.
$N{H}_{4}Cl\to N{H}_4^{+}+C{l}^{-}$
$N{H}_{4}OH\leftrightarrow N{H}_4^{+}+O{H}^{-}$