`FeSO_4` solution mixed with `(NH_4)_2SO_4` solution is `1:1` molar ratio gives the test of `Fe^(2+)` ion but `CuSO_4` solution mixed with aqueous ammonia in `1:4` molar ratio does not give the test of `Cu^(2+)` ion. Explain why?

Explanation

`FeSO_(4)` solution mixed with `(NH_(4)), S04` solution in `1:1` molar ratio forms a double salt, `FeSO4(NH_(4))_(2)SO_(4)-6H_(2)O` (Mohr's salt) which ionizes in the solution to give `Fe^(2+)` ions Hence it gives the tests of `Fe^(2+)` ions `CuSO_(4)` solution mixed with aqueous ammonia in `1:4` molar ratio forms a complex salt, with the formula `[CU(NH_(3))_(4)]SO_(4)` The complex ion `[Cu(NH_(3))_(4)]^(2+)` does not ionize to give `Cu^(2+)` ions Hence, it does not give the tests of `Cu^(2+)` ion.