Question

In the third group of qualitative analysis, the precipitating reagent is $N{H}_{4}Cl+N{H}_{4}OH$. The function of $N{H}_{4}Cl$ is to_______

• A. increase the ionization of $N{H}_{4}OH$
• B. suppress the ionization of $N{H}_{4}OH$
• C. stabilise the hydroxides of group cations
• D. convert the ions of group third into their respective chlorides

Answer 1

Answer: (B)

suppress the ionization of $N{H}_{4}OH$

Common ion effect is observed when a solution of weak electrolyte is mixed with a solution of a strong electrolyte, which provides an ion common to that provided by a weak electrolyte.

The $N{H}_{4}OH$ is weak base it does not ionises completely. Thus due to presence of common ion $N{H}_4^{+}$ in $N{H}_{4}Cl$, it suppresses the ionisation of weak base $N{H}_{4}OH$ in order to decrease the $O{H}^{-}$ concentration so that higher group cations will not get precipitated.

Thus the pair $N{H}_{4}OH+N{H}_{4}Cl$ shows common ion effect.

Ammonium chloride suppresses the ionization of ammonium hydroxide.

Option B is correct.