explain chemistry of lassigne test
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Objective:
Our objective is to detect the presence of nitrogen, sulphur, chlorine, bromine and iodine in organic compounds by Lassaigne's test.
The Theory:
Carbon is the main constituent element of all organic compounds. Hydrogen is also present in most of the organic compounds, but there are few exceptions, such as: CCl4, CS2 , etc. Elements other than these elements such as nitrogen, sulphur and halogens (chlorine, bromine and iodine) may also be present in organic compounds. These extra elements are usually detected by Lassaigne's Test that was developed by the French Chemist J.L Lassaigne. In this test, the organic compound is fused with metallic sodium to convert these elements into water soluble sodium salt. Usual qualitative tests are performed on this extract for the detection of respective elements.
Detection of Nitrogen
If nitrogen is present in the compound, the Lassaigne's extract would contain sodium cyanide formed during fusion. Sodium cyanide is converted to sodium ferrocyanide on treating with ferrous sulphate. On further treating it with ferric chloride, a prussian blue complex, ferricferrocyanide is formed.





Our objective is to detect the presence of nitrogen, sulphur, chlorine, bromine and iodine in organic compounds by Lassaigne's test.
The Theory:
Carbon is the main constituent element of all organic compounds. Hydrogen is also present in most of the organic compounds, but there are few exceptions, such as: CCl4, CS2 , etc. Elements other than these elements such as nitrogen, sulphur and halogens (chlorine, bromine and iodine) may also be present in organic compounds. These extra elements are usually detected by Lassaigne's Test that was developed by the French Chemist J.L Lassaigne. In this test, the organic compound is fused with metallic sodium to convert these elements into water soluble sodium salt. Usual qualitative tests are performed on this extract for the detection of respective elements.
Detection of Nitrogen
If nitrogen is present in the compound, the Lassaigne's extract would contain sodium cyanide formed during fusion. Sodium cyanide is converted to sodium ferrocyanide on treating with ferrous sulphate. On further treating it with ferric chloride, a prussian blue complex, ferricferrocyanide is formed.





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Hey !!
In this test, a fleshly cut pea-size sodium metal is placed in a fusion tube and strongly heated till it forms a shining globule. The fusion tube is withdrawn from the flame and a pinch of organic halide added. The fusion tube is again heated in the flame to red-heat and then plunged into distilled water and filtered. The filtrate thus obtained is called ''Lassaigne's extract''
The Lassaigne's extract is then boiled with the dil. HNO₃ to expel gases, if evolved. The solution is then cooled and AgNO₃ solution added to it.
(a) A white precipitate soluble in NH₄OH indicates the presence of chlorine.
(b) A pale yellow precipitate partially soluble in NH₄OH indicates the presence of bromine.
(c) A bright yellow precipitate insoluble in NH₄OH indicates the presence of halogens.
Good luck !!
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