The use of `NH_4Cl` in the detection of third group radicals is to

Options

A. decrease the solubility of the hydroxides of the group III cations
B. counter the activity of any interfering anions
C. prevent the precipitation of group IV cations as hydroxides
D. ensure complete precipitation of the third group cations.

Answer

C

Explanation

The group reagent for group III is `NH_4Cl` followed by `NH_4OH`.The purpose of adding `NH_4Cl` is to suppress the ionization of `NH_4OH(NH_4 undersetlarr to NH^(4+) + OH^(-))` by common ion effect so as to decrease the `OH^-` ion concentration. At the reduced `OH^-` concentration, the ion products of the group IV metal hydroxides do not exceed their solubility products and , so their precipitation is prevented.