Question

Which of the following set of elements can be detected by Lassaigne’s test

(1) N, S only 

(2) N, P, S only 

(3) Halogens P only 

(4) N, P, S, halogens

Answer 1

(4) N, P, S, halogens

Nitrogen, sulphur, halogens and phosphorus present in an organic compound are detected by Lassaigne’s test.

Answer 2

Nitrogen, 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)

The formed ionic salts are extracted from the fused mass by boiling it with distilled water. This is called sodium fusion extract.