FeSO4 solution mixed with '(NH4)2 SO4' solution in 1 : 1 molar ratio gives the test of 'Fe^2+' ion but 'CuSO4' solution mixed with aqueous ammonia in'1 : 4 molar ratio does not give the test of 'Cu^2+' ion. Explain why?

Explanation

Because .FeSO_4. forms .only a double salt .FeSO_4^*(NH_4^prime)_2 SO_4^* 6 H_2 O .. with ..(NH_3)_4^8)_2 SO_4^*.. The
double salt dissociates completely. into ions. But .CuSO_4. forms a complex.When treated with .NH_3,[Cu(NH_3)_4] SO_4. in which
.Cu^2 *. is a part of the coordination sphere. Hence the cómplex will not give test of .Cu^2 *.