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

Explanation

Lassaigne.s Test : -
`to` A small dry sodium piece is taken in a fusion tube and heated gently till the sodium melts.
`to` To this molten sodium a small amount of organic compound is added and heated until it changes red hot.
`to` This red hot tube is plunged in a china dish containing water and this content is boiled, cooled and filtered
`to` The obtained filtrate is known as Lassaigne.s extract.
`to` This test is used to detect the elements Nitrogen, Sulphur, halogens etc.,
Detection of Nitrogen :
The Lassaigne.s extract is made alkaline by adding few drops of dol. NaOH. to this freshly prepared `FeSO_(4)` solution is added and warmed then few drops of `FeCl_(3)` are added followed by acidification with Conc. HCl (or) `H_(2)SO_(4)` bluish green colouration indicates the nitrogen.
`Na + C + N to Na CN`
`2 Na CN + Fe SO _(4) to Na SO _(4) + Fe (CN) _(2)`
`Fe (CN) _(2) + 4 Na CN to Na _(4) [Fe (CN) _(6)]`
`3Na _(4) [Fe (CN) _(6) ] + 4 Fe Cl _(3) to Fe _(4) [Fe (CN) _(6) ]_(3) + 12 Na Cl`
Prussian blue colouration
(b) Detection of Halogens : The sodium fusion extract is acidified with `HNO _(3)` and is treated with `AgNO _(3)` solution
`Ag + X to Ag X`
`to ` White PPt indjcates `Br^(o+)` ion
`to` Pale yellow PPt indjcates `Br ^(o+)` ion
`to` Yellow PPt indicates `l ^(o+)` ion
(c ) Detection of Sulphure : To the sodium extract freshly prepared sodium nitroprusside solution. A deep violet colouration takes place.
`S ^(-2) + [ Fe ( CN) _(5) NO]^(2+) underset( "Violet") ( [Fe (CN) _(5) NOS]^(4-))`