Question

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

Answer 1

Step 1 : To determine the structure of compound (B).

$Ca{C}_2+2H_{2}O\to HC\equiv CH+Ca(OH{)}_2$

Cal. carbide Acetylene (B)

Step 2 : To determine the structure of compound (A). Since compound (B), i.e., acetylene is produced by warming compound (A) with silver powder, therefore, compound (A) must be chloroform.

$CHC{l}_3+6Ag+C{l}_{3}CH\stackrel{\Delta }{\to }HC\equiv CH+6AgCl$

Chloroform (A) Acetylene (B)

The fact that compound (A) is actually chloroform is confirmed by the observation that (A) is slowly oxidized by air in presence of light to a highly poisonous gas, i.e., phosgene.

$2CHC{l}_3+O_2\stackrel{h\nu }{\to }2COC{l}_2+2HCl$

Chloroform (A) Phosgene

(poisonous gas)

Thus, $A=CHC{l}_3$ (chloroform) and $B-HC\equiv CH$ (acetylene)