Among Fe3+, Pb2+, Cu2+ and Mn2+, identify the one that gets precipitated out while passing H2S in presence of NH4OH as group reagent. The highest possible oxidation state of the corresponding metal is
- +3
- +4
- +2
- +7
Answer
(4) +7
Solution
Group reagents: Pb2+, Cu2+ – group II (H2S in dil. HCl); Fe3+ – group III (NH4OH in presence of NH4Cl, as Fe(OH)3); Mn2+ – group IV (H2S in presence of NH4OH).
In ammoniacal medium H2S ionises more, [ S2-] becomes high and the ionic product exceeds Ksp of MnS ⇒ Mn2+ + S2- MnS (buff coloured precipitate).
Mn (3d5 4s2) shows a highest oxidation state of +7 (e.g. KMnO4, Mn2O7).
Answer: (4)