Question

The compound formed in the positive test for nitrogen with the Lassaigne's solution of an organic compound is:

• A. $F{e}_4\left[Fe\right(CN{)}_6{]}_3$
• B. $N{a}_3\left[Fe\right(CN{)}_6]$
• C. $Fe(CN{)}_3$
• D. $N{a}_3\left[Fe\right(CN{)}_{5}NOS]$

Answer 1

The correct option is A $F{e}_4\left[Fe\right(CN{)}_6{]}_3$

The 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.

$Na+C+N\to NaCN$

$6NaCN+FeS{O}_4\to \underset{\text{Sodium ferrocyanide}}{N{a}_4\left[Fe\right(CN{)}_6]}+N{a}_{2}S{O}_4$

$N{a}_4\left[Fe\right(CN{)}_6]+F{e}^{3+}\to \underset{\text{Ferric ferrocyanide}}{F{e}_4\left[Fe\right(CN{)}_6{]}_3}$

Option A is correct.