Indentify the following ions by a simple test forming complex compound :
(i) ` Cu^(2+) ` (ii) ` Ni^(2+) ` (iii) ` Fe^(3+)` (iv) ` Co^(2+) `

Explanation

(i) ` Cu^(2+) ` solution with excesses of ammonia solution, `NH_(4)OH` froms a deep blue coloured complex.
` underset(ap)(Cu^(2+)) + 4NH_(4)OH_(aq) to [Cu(NH_(3))_(4)]^(2+) + 4H_(2)O`
(b) ` Cu^(2+) ` with potassium hexacyanoferrate (II) forms red - brown precipitate which is a complex, ` Cu_(2) [Fe(CN)_(6)]`
` 2Cu^(2+) + K_(4)[Fe(CN)_(6)] to Cu_(2)[Fe(CN)_(6)]`
red brown
(ii) `Ni^(2+)` with dimethylgloxine (DMG) in ammonical alcoholic solution forms rosy-red precipitate of a complex.
` (##NVT_21_CHE_XII_C18_E01_001_S01.png" width="80%">
(iii) (a) ` Fe^(3+) ` with `K_(4)[Fe (CN)_(6)]` forms prussian blue compound of deep blue colour .
` Fe^(3+) + K_(4)[Fe(CN)_(6)] to overset(III" "II )(K[Fe(CN)_(6))] + 3K^(+)`
prussian blue
(b) ` Fe^(3+) ` with ammonium thiocyanate `NH_(4)SCN` forms deep red compound .
` Fe^(3+) + 3NH_(4)SCN to underset("deep red")(Fe(SCN)_(3)) + 3NH_(4)^(+)`