Write the equations involved in the detection of Nitrogen, Halogens and Sulphur in or-ganic compounds.

Explanation

Lassaigne's Test: In Lassaigne's test, the organic compound is mixed with sodium metal and fused strongly. The fused mass is extracted with water by plunging the red hot ignition tube in distilled water and the contents are boiled for 5 minutes and filtered. The filtrate is called Sodium extract or Lassaigne's extract.
If nitrogen is present in the organic compound, it reacts with sodium and carbon forming sodium cyanide.
`underset("form organic compound")(Na ubrace(C+N)toNaCN`
If sulphur is present in the organic compound, it reacts.with sodium forming sodium sulphide.
`2Na+StoNa_(2)S`
If halogens are present in the organic compound, they form sodium halides.
`2Na+Xto2NaX(X=Xl,Br` or `I)`
Test for Nitrogen: A little of the Lassaigne's extract is made alkaline with NaOH solution and then freshly prepared `FeSO_(4)` solution is added. To it 2-3 drops of `FeCl_(3)` solution is added, cooled and acidified with conc. HCI.
A prussian blue or green ppt. or colouration Is observed.
`FeSO_(4)+2NaOHtoFe(OH)_(2)+NA_(2)SO_(4)`
`6NaCN+Fe(OH)_(2)tounderset("Sodium ferrocyanide")(Na_(4)[Fe(CN)_(6)]+2NaOH)`
`3Na_(4)[Fe(CN)_(6)]+4FeCl_(3)tounderset("Ferric ferrocyanide")(Fe_(4)[Fe_(CN)_(6)]+12NaCl)`
Test for Halogens: A little of the Lassaigne's extract is acidified with nitric acid and treated with `AgNO_(3)` solution.
If white ppt. soluble in `NH_(4)OH` is formed, the halide is `Cl^(-)`. Hence, chlorine is present.
If pale yellow ppt. partially soluble in `NH_(4)OH` is formed, the halide is `Br^(-)`. Hence, bromine is present.
If yellow ppt. insoluble in `NH_(4)OH` is frmed, the halide is `I^(-)`. Hence, iodine is present.
Test for Sulphur: To a little of the Lassaigne's extract freshly prepared sodium nitroprusside solution is added. Deep purple colouration is observed.
`underset("sodium nitroprusside")(Na_(2)S+Na_(2)[Fe(CN)_(5)NO])tounderset("purple coloured complex")(Na_(4)[Fe(CN)_(5)NOS])`