Give a method for the qualitative detection of nitrogen.

1.	Give a method for the qualitative detection of nitrogen.
Answer» The sodium fusion extract is boiled with iron(II) sulphate and then acidified with concentrated sulphuric acid. The formation of Prussian blue colour confirms the presence of nitrogen. Sodium cyanide first reacts with iron(II) sulphate and forms sodium hexacyanoferrate(II). On heating with concentrated sulphuric acid some iron(II) ions are oxidised to iron(III) ions which react with sodium hexacyanoferrate(II) to produce iron(III) hexacyanoferrate(II) (ferriferrocyanide) which is Prussian blue in colour. 6CN^– + Fe²⁺ → [Fe(CN)6]^4– 3[Fe(CN)6]₄– + 4Fe3⁺ Fe4[Fe(CN)₆]3.xH₂O Prussian blue

Answer»

The sodium fusion extract is boiled with iron(II) sulphate and then acidified with concentrated sulphuric acid. The formation of Prussian blue colour confirms the presence of nitrogen. Sodium cyanide first reacts with iron(II) sulphate and forms sodium hexacyanoferrate(II). On heating with concentrated sulphuric acid some iron(II) ions are oxidised to iron(III) ions which react with sodium hexacyanoferrate(II) to produce iron(III) hexacyanoferrate(II) (ferriferrocyanide) which is Prussian blue in colour.

6CN^– + Fe²⁺ → [Fe(CN)6]^4–

3[Fe(CN)6]₄– + 4Fe3⁺ Fe4[Fe(CN)₆]3.xH₂O

Prussian blue

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