Question -
Answer -
In the Lassaigne’s testfor nitrogen in an organic compound, the sodium fusion extract is boiled withiron (II) sulphate and then acidified with sulphuric acid. In the process,sodium cyanide first reacts with iron (II) sulphate and forms sodiumhexacyanoferrate (II). Then, on heating with sulphuric acid, some iron (II) getsoxidised to form iron (III) hexacyanoferrate (II), which is Prussian blue incolour. The chemical equations involved in the reaction can be represented as
Hence, the Prussian bluecolour is due to the formation of Fe4[Fe(CN)6]3.