Write two difference between double salt and complex compound.

Explanation

(a) `FeSO_4` solution mixed with `(NH_4)_2SO_4` solution in 1 : 1 molar ratio forms a double salt, `FeSO_4(NH_4)_2SO_4.6H_2O` (Mohr salt) which ionizes in water to give `Fe^(2+)` ions alongwith `NH_4^(+)` and `SO_4^(2-)` ions. Hence, it gives the tests of `Fe^(2+)` ions.
(b) `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`. This will ionise to give `SO_4^(2-)` and the complex ion `[Cu(NH_3)_4]^(2+)`. 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+)` ions.