Question

`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?

Answer 1

`FeSO_(4)` does not form any complex with `(NH_(4))_(2)SO_(4)` instead , they form a double salt `FeSO_(4)(NH_(4))_(2)sO_(4)6H_(2)O` which dissociates completely into ions but `CuSO_(4)` combines with NH to form the complex `[Cu(NH_(3))_(4)]SO_(4)` in which complex ion , `[Cu(NH_(3))_(4)]^(2+)` does not dissociate to give `Cu^(2+)` ions.