AP EAMCET Engineering 21 Apr 2019 Shift 2 Paper

Lassaigne's test is used to detect the presence of N,S,Cl,Br,I in organic compounds using sodium fusion extract. In the case of nitrogen, Prussian blue colour is obtained due to the formation of Fe4[Fe(CN)6]3. Reactions involved in this are as follows
Na+

C+N

C&N from organic compund

→NaCN

FeSO4+NaOH→Fe(OH)2+Na2SO4

Fe(OH)2+

2NaCN

Obtained from sodium extract

→Fe(CN)2+2NaOH

Fe(CN)2+4NaCN→Na4[Fe(CN)6]

3Na4[Fe(CN)6]+4FeCl3→

Fe4[Fe(CN)6]3

Ferric ferrocyanide (Prussian blue coloured compound)

+12NaCl