Qualitative Analysis of Manganese (II) Ion
Take the original solution and add NH4OH to make it alkaline. Pass hydrogen sulphide gas (H2S) through the solution, a precipitate is obtained. Formation of buff (flesh coloured) precipitate indicates the presence of Mn2+.
Mn2+ + S2- → MnS
Confirmatory Test
Buff coloured precipitate of MnS dissolves in dilute HCl.
MnS + 2HCl → MnCl2 + H2S
Boil off hydrogen sulphide gas. To the solution obtained, on adding NaOH, a white precipitate of Mn(OH)2 is obtained. The precipitate rapidly oxidises on exposure to air turning brown.
Mn2+ + 2OH- → Mn(OH)2 (Manganese hydroxide, white precipitate)
Mn(OH)2 + O2 → MnO2 + H2O