Question

A sweet smelling organic compound (A) is slowly oxidised by air in the presence of light to a highly poisonous gas. On warming with silver powder, it forms a gaseous substance (B) which is also formed by the action of calcium carbide on water. Identify (A) and (B), and write the chemical equations of the reactions involved.

Answer 1

Compound (A) is chloroform, (CHCl₃), a sweet-smelling organic compound, and compound (B) is acetylene (C₂H₂). Chloroform slowly oxidizes in the presence of air and light to form phosgene(COCl₂) a highly poisonous gas. When chloroform is heated with silver powder, it undergoes dehalogenation to produce acetylene, which is also formed from the reaction of calcium carbide (CaC₂) with water.

1. Oxidation of chloroform (A): When chloroform is exposed to air and light, it slowly oxidizes to form phosgene, a highly poisonous gas.
   \[\ce{2CHCl3 + O2 ->[hv][]2COCl2 + HCl}\]
   This reaction forms phosgene, a highly toxic gas, and is why chloroform is stored in dark bottles.
2. Reaction of Chloroform (A) with Silver Powder: When chloroform is heated with silver powder, it undergoes dehalogenation to produce acetylene.
   \[\ce{2CHCl3 + 6Ag ->[Δ][]C2H2 + 6AgCl}\]
   This dehalogenation reaction produces acetylene.
3. Formation of Acetylene (B) from Calcium Carbide: This reaction demonstrates that substance (B), acetylene, is formed by the action of calcium carbide on water.
   \[\ce{CaC2 + 2H2O ->[][]C2H2 + Ca(OH)2}\]