Qualitative Organic: Nitrogen

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In Lassaigne's test, presence of nitrogen is confirmed by formation of a Prussian blue complex due to:

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1. **Sodium Fusion**: The organic compound is fused with metallic $Na$. If Nitrogen is present, it forms Sodium Cyanide ($NaCN$).
2. **Extract preparation**: The fusion mass is extracted with water, filtered, and treated.
3. **Step 1**: Freshly prepared $FeSO_4$ is added. Cyanide reacts with $Fe^{2+}$ to form hexacyanoferrate(II).
4. **Step 2**: The solution is acidified with concentrated $H_2SO_4$. During this, some $Fe^{2+}$ is oxidized to $Fe^{3+}$.
5. **Color Formation**: The $Fe^{3+}$ reacts with the ferrocyanide to form **Ferri-ferrocyanide ($Fe_4[Fe(CN)_6]_3$)**, which manifests as an intense **Prussian blue** color.
6. **Result**: This confirms the presence of Nitrogen.

Qualitative Organic: Nitrogen

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