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Detection of Nitrogen:
Procedure:
Step 1:
Take 2ml of lassaigne’s filtrate in a test tube and add a few drops of sodium hydroxide (NaOH) solution to it.

Step 2:
Now add a few ml of freshly prepared ferrous sulphate (FeSO4) solution to the test tube.

Step 3:
Boil the solution.

The sodium cyanide formed during the preparation of lassaigne’s solution is converted to sodium Ferrocyanide.

Step 4:
Add a few drops of FeCl3 solution to a test tube.
Finally, acidify it with concentrated HCl.


The appearance of blue or greenish-blue ( Prussian blue ) colour or ppt of ferric ferrocyanide proves the presence of nitrogen in the organic compound.

If a blood-red colour appeared instead of Prussian blue colour then it proves that both nitrogen and sulphur are present in an organic compound.
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