Question

The compound formed in the positive test for nitrogen with the lassaigne solution of an organic compound is

Answer 1

initially during the preparation of sodium fusion extract Nitrogen present in compound is converted to cyanide.
1)Na + C + N ---> NaCN

on adding ferrous sulphate to extract and boiling NaCN is converted to sodium Ferro cyanide.
2) 6NaCN + FeSO4 ----> Na4 [Fe (CN)6] +Na2SO4

then on acidification with dil.H2SO4 gives
iron (III) hexacyanoferrate (II) which is prussian blue in Color and confirms presence of nitrogen.
3) 3Na [Fe (CN)6] +2Fe (SO4)3---->
Fe4 [Fe (CN)6]3 +6Na2SO4