Why is ammonium chloride added before addition of ammoniun hydroxide in preciptn of grp 3 cations?
Asked by | 26th Jan, 2009, 03:27: PM
This is to prevent the precipitation of hydroxides of higher groups.
Ammonium chloride is a strong electrolyte. SO, it dissociates completely.
NH4Cl NH4+ + Cl-
Now when NH4OH is added, due to common ion effect its dissociation is supressed.
NH4OH NH4+ + OH-
The concentration of hydroxide ion is less. Hence, the ionic product of hydroxide ion and cation only exceeds the solubility product of hydroxides of group 3 cations and they are precipitaed. The solubility product of higher group cations is higher than their ionic product and hence they are not precipitated.
Answered by | 6th Feb, 2009, 04:47: PM
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