Question

A mixture containing four miscible liquids P, Q, R and S are subjected to fractional distillation. Liquid P is distilled off first, into the receiver flask. Then S, followed by R and Q is left behind in the distillation flask. Based on the above observations arrange the liquids in ascending order of their vapor pressures.

Answer 1

Fractional distillation is based on the process of the difference in the boiling points of the substances present in the mixture. The substances having the lower boiling point will be distilled first and thus, the substances having lower point, will be distilled out in the last.

Complete answer:
- By fractional distillation we mean the chemical process of separating the mixture( consisting of a large number of substances, compounds and elements all together) into its constituents’ substances .
- In the fractional distillation ,process boiling point plays a very important role. Boiling point of any substance is the temperature at which any substance changes into its vapor phase. The one having the lower boiling point will distill out first . so, from the given gases, the gas having the lower boiling point will distill out first.
Now considering the statement as;
- From the given statement, we can see that the P distills out first i.e. it has the lowest boiling point of all; followed by S, then R and at the last Q will be distilled out.
Thus, the ascending order of the gases in which they will get distilled out is: $P>S>R>Q$ .

Note: Fractional distillation is mostly used for only those mixtures of substances in which the substances have not much difference in their boiling points and cannot be separated through any other means.