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Why do we add excess of NH(4)Cl and NH(4...

Why do we add excess of `NH_(4)Cl` and `NH_(4)OH` in the precipitation of group III cations?

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The solubility product of hydroxides of cations of group III is extremely low.
`NH_(4)Cl` suppressess the ionisation of `NH_(4)OH`to a great extent due to common ion effect As a result low concentration of `OH^(ɵ)` is made available for precipitating group III cation hydroxides. other hydroxides remain in solution as they required higher concentration of `OH^(ɵ)` ions for precipitations as hydroxides.
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The role of NH_(4)Cl in the precipitation of the hydroxides of group III cations is to:

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