Question 12.28:
Explain, why an organic liquid vaporises at a temperature below its boiling point in its
steam distillation?


In steam distillation, the organic liquid starts to boil when the sum of vapour pressure due
to the organic liquid (p1) and the vapour pressure due to water (p2) becomes equal to
atmospheric pressure (p), that is, p = p1 + p2
Since p1 < p2, organic liquid will vapourise at a lower temperature than its boiling point.