What is Lassaigne Test ?
Write down chemical reaction to support your answer.
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Explanation:
Nitrogenn, Sulphur, and halogens present in organic compounds are detected by Lassaigne’s test. Here, a small piece of Na metal is heated in a fusion tube with the organic compound. The principle is that, in doing so, Na converts all the elements present into ionic form.
Na + C + N → NaCN
2Na + S → Na2S
Na + X → NaX ( X= Cl, Br, or I)
Test for Nitrogen
The extract is boiled with FeSO4 and acidified with concentrated H2SO4. The appearance on Prussian blue colour indicates the presence of nitrogen.
The following reactions occur,
Fe2+ + 6CN– → [Fe(CN)6]4-
Fe2+ + H+→ Fe3+ + e–
[Fe(CN)6]4- + 4Fe3+ → Fe4[Fe(CN)6].H2O
Test for Sulphur
The extract is treated with sodium nitroprusside. The appearance of violet colour indicates the presence of sulphur.
The following reaction occurs:
S2- + [Fe(CN)5NO]2- → [Fe(CN)5NOS]4-