Analytical ChemistryHard
Question
A white crystalline substance dissolves in water. On passing H2S in this solution, a black precipitate is obtained. The black precipitate dissolves completely in hot HNO3. On adding a few drops of concentrated H2SO4, a white precipitate is obtained which is soluble in ammonium acetate. The white precipitate is that of:
Options
A.BaSO4
B.SrSO4
C.PbSO4
D.Ag2SO4
Solution
The white precipitate obtained with H2SO4 is that of PbSO4. The white crystalline substance may be that of Pb(NO3)2.
Pb2+ + S2- → PbS ↓ (black) ; 3PbS ↓ + 8HNO3 → 3Pb2+ + 6NO3- + 3S ↓ + 2NO + 4H2O
Pb2+ + SO42- → PbSO4 ↓ (white)
PbSO4 + 2CH3COONH4 → (CH3COO)2Pb + (NH4)2SO4
BaS and SrS precipitates are not black in colour. Ag2SO4 is white precipitate but does not dissolve in ammonium acetate.
Pb2+ + S2- → PbS ↓ (black) ; 3PbS ↓ + 8HNO3 → 3Pb2+ + 6NO3- + 3S ↓ + 2NO + 4H2O
Pb2+ + SO42- → PbSO4 ↓ (white)
PbSO4 + 2CH3COONH4 → (CH3COO)2Pb + (NH4)2SO4
BaS and SrS precipitates are not black in colour. Ag2SO4 is white precipitate but does not dissolve in ammonium acetate.
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