Analytical ChemistryHard

Question

Co2+ + KCN (not in excess) → precipitate.
Select the correct statement(s) with respect to the precipitate.

Options

A.It is yellow in colour.
B.It is reddish-brown in colour.
C.It dissolves in excess of the reagent forming a brown solution.
D.It is obtained when brown solution (option (C)) is acidified with dilute HCl in the cold.

Solution

Co2+ + 2CN-  → Co(CN)2↓ (reddish - brown)
Co(CN)2 ↓ + 4CN- (excess) → [Co(CN)6]4- (brown solution)
[Co(CN)6]4- + 4H+ →  Co(CN)2 ↓ + 4HCN.

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