Analytical ChemistryHard
Question
A coloured solution of an inorganic salt reacts with potassium thiocyanate to give first a black precipitate, which slowly turns white. The salt solution also gives black precipitate with H2S gas in slightly acidic medium. The black precipitate dissolves in potassium cyanide forming a colourless solution. The basic radical present in the inorganic salt is :
Options
A.Bi3+
B.Cu2+
C.Hg2+
D.None
Solution
Cu2+ + 2SCN- → Cu(SCN)2↓ (black)
2Cu(SCN)2 → 2CuSCN↓ (white) + (SCN)2
Cu2+ + H2S
CuS↓ (black) + 2H+
2CuS↓ + 8CN- → 2[Cu(CN)4]3- + S22-
2Cu(SCN)2 → 2CuSCN↓ (white) + (SCN)2
Cu2+ + H2S
CuS↓ (black) + 2H+2CuS↓ + 8CN- → 2[Cu(CN)4]3- + S22-
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