Sodium extract solution is prepared and 1ml of that Na extract
solution is taken in a clean test-tube and added few drops of sodium hydroxide
solution if sodium extract solution is not Alkaline. To this solution 1ml of
freshly prepared ferrous sulphate is added. Whole solution is then heated to
boiling for few minutes. The solution is then cooled under tap . To this cooled
solution 8-10 drops of concentrated hydrochloric acid is added and 1 drop of
ferric chlorite solution is added. After this, apperance of Prussian blue
or green precipitation of ferric ferrocynate conforms the presence of Nitrogen
in given organic compound.
Reaction
involved :
1.
Organic
compound containing Nitrogen during sodium fusion give NaCN which is water
soluble ionic salt so sodium extract solution contain NaCN.
Na + C + N
----------------> NaCN
2. Excess
of sodium if remained reacts with water to give NaOH.
Na + H2O ------------------>
NaOH + H2
3. This sodium
hydroxide solution and added NaOH reacts with ferrous sulphate to give ferrous
hydroxide which has dirty green colour.
FeSo4 + 2NaOH
----------------> Fe(OH)2 + Na2So4 (dirty green ppt)
4. Ferrous
hydroxide then reacts with NaCN to give sodium ferrocyanide.
Fe(OH)2 + 6NaCN
----------------> Na4[Fe(CN)6] + NaOH (sodium ferrocyanide)
5. Sodium
ferrocyanide then reacts with ferric chloride solution to give ferric
ferrocyanide which has prussion blue or green colour which comforms the
presence of Nitrogen.
3Na4[Fe(CN)6] +
4FeCl3 ---------------> Fe4[Fe(CN)6]3 (ferric cyanide) + 12NaCl
(if the product
formed upon reacting with conc HCl gives Prussian blue or green colour
then we
can comform the presence of Nitrogen in given organic compound)
Sometimes during
Nitrogen test there is the formation of blood red colour which shows the
presence of both Nitrogen and sulphur in given organic compound. If the organic
compound contains N as well as S during sodium fusion there will be the
formation of NaCN instead NaCN which directly reacts with feric chloride
solution to give ferric thio cynite which has blood red colour.
Na + S + C + N
---------------> NaCN (Sodium thio cyanide)
NaCN + FeCl3
----------------> Fe(CNS)3 (ferric sulphocyanide, blood red)
0 comments: