JEE Main Chemistry Class 12 Analytical Chemistry Questions

(A) Lassaigne test is used to detect N,S,P,X elements.
The elements present in the compound are converted from covalent form into the ionic form by fusing the compound with sodium metal. Following reactions take place.
Na+C+N

∆

⟶

NaCN
2Na+S

∆

⟶

Na2S
Na+X

∆

⟶

NaX‌‌(X=Cl,Br or l)
(B) Carbon and hydrogen are detected by heating the compound with copper (II) oxide.
C+2CuO⟶2Cu+CO2
2H+CuO⟶Cu+H2O
(C) Halides are detected by silver nitrate.
They form precipitate of AgX except fluorine.
Ag+(aq)+X−(aq)⟶AgX(s)
(D) Sodium fusion extract gives black precipitate of PbS with acetic acid and lead acetate to confirm the presence of sulphur.