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Due to common ion effect (NH 4 + ions), NH 4 Cl reduces the ionisation of NH 4 OH. Then hydroxides of III group only (but not of those of IV group) are precipitated.

Equilibrium

Question

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During qualitative analysis, why NH₄Cl and NH₄OH are added in the III group?

Answer

Due to common ion effect (NH₄⁺ ions), NH₄Cl reduces the ionisation of NH₄OH. Then hydroxides of III group only (but not of those of IV group) are precipitated.