Why NH4Cl is added before adding NH4OH in group 3??
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♣️In salt analysis NH4Cl is added in sufficient amount before adding NH4OH because otherwise the cations of higher group may get precipitated in group III.
Reason: NH4Cl is strong electrolyte, it decomposes completely. While the NH4OH is weak base it does not ionises completely. Thus due to presence of common ion NH4 + in NH4Cl, it supresses the ionisation of weak base NH4OH in order to decrease the OH- concentration so that higher group cations will not get precipitated.
Common ion effect:
NH4Cl → NH4 + + Cl-
NH4OH ↔ NH4 + + OH-
Reason: NH4Cl is strong electrolyte, it decomposes completely. While the NH4OH is weak base it does not ionises completely. Thus due to presence of common ion NH4 + in NH4Cl, it supresses the ionisation of weak base NH4OH in order to decrease the OH- concentration so that higher group cations will not get precipitated.
Common ion effect:
NH4Cl → NH4 + + Cl-
NH4OH ↔ NH4 + + OH-
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