Organic Chemistry Some Basic Principles and Techniques - Result Question 57
####63. In steam distillation of toluene, the pressure for toluene in vapour is
[2001]
(a) Equal to pressure of barometer
(b) Less than pressure of barometer
(c) Equal to vapour pressure of toluene in simple distillation
(d) More than vapour pressure of toluene in simple distillation
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Solution:
- (b) The principle of steam distillation is based on Dalton’s law of partial pressures. Suppose $p_1$ and $p_2$ be the vapour pressures of water vapour and the toluene at the distillation temperature. Toluene boils when total pressure is equal to atmospheric pressure $p$ i.e $p=p_1+p_2$
or $p_2=p-p_1$
As a result, when toluene boil in the presence of steam its partial pressure $p_2$ is less than atmospheric pressure.
