Question

In the Lassaigne's test for the detection of nitrogen in the organic compound, the blue coloured compound formed is:

• A. ferric ferricyanide
• B. ferrous ferricyanide
• C. ferric ferrocyanide
• D. ferrous ferrocyanide

Answer 1

The correct option is C ferric ferrocyanide

Carbon and nitrogen present in the organic compound on fusion with sodium metal gives sodium cyanide $\left(NaCN\right)$ soluble in water.

This is converted into sodium ferrocyanide by the addition of sufficient quantity of ferrous sulphate.

Ferric ions generated during the process react with ferrocyanide to form prussian blue precipitate of ferric ferrocyanide.

$Na+C+N⟶NaCN$

$6NaCN+FeSO4⟶\underset{sodiumferrocyanide}{\underset{}{Na4\left[Fe\right(CN\left)6\right]}}+N{a}_{2}S{O}_4$

$N{a}_4\left[Fe\right(CN{)}_6]+F{e}_3^{+}⟶\underset{Fericferrocyanide}{\underset{}{F{e}_4\left[Fe\right(CN{)}_6{]}_3}}$