Question

Sodium fusion extract, obtained from aniline, on treatment with iron (II) sulphate and $H_{2}S{O}_4$ in presence of air gives a Prussian blue precipitate. The blue colour is due to the formation of:

• A. $F{e}_4\left[Fe\right(CN{)}_6{]}_3$
• B. $F{e}_3\left[Fe\right(CN{)}_6{]}_2$
• C. $F{e}_4\left[Fe\right(CN{)}_6{]}_2$
• D. $F{e}_3\left[Fe\right(CN{)}_6{]}_3$

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 give 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 the prussian blue precipitate of ferric ferrocyanide.

The Prussian blue colour is due to formation of ferric ferrocyanide, $F{e}_4\left[Fe\right(CN{)}_6{]}_3$.