Question

Colour of solution when bromide ion nd lead acetate are mixed

Answer 1

Actually, this is a characteristic test for the presence of ferric ions and for thiocyanate ions. Cyanide ions are nowhere directly involved in the formation of ferric(III) thiocyanate. If we review the test procedure for the detection of cyanide ions, we find that we add, according to our choice, either thiosulphate ions or S22- ions. These ions disproportionate in the presence of cyanide ions, forming thiocyanate ions. It is these thiocyanate ions that eventually react with the added ferric ions to give the blood red complex formation

CN- + S2O32- -> SCN- + SO32-

CN- + S22- -> SCN- + S2-

Fe3+ + SCN- -> Fe(SCN)2+