When a mixture of three miscible liquids is subjected to fractional distillation, liquid B is obtained in the receiver flask. The remaining mixture on further fractional distillation flask, A, is left behind in the distillation flask. On the basis of the results, comment on the critical temperatures of A, B and C when they are gaseous state.

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Solution

Critical temperature: It is defined as the temperature above which a gas can not liquefy whatever pressure may apply.
Fractional distillation: It is the method used for the separation of a mixture of liquid on the basis of their boiling point.
Liquid B,
Liquid B is first obtained in the receiver flask.
This means liquid B has a low boiling point.
Therefore it will vaporize first and condensed to convert into liquid again.
The first vaporization of liquid B concludes that it has low intermolecular forces of attraction between its molecules.
Low intermolecular forces of attraction between molecules mean low critical temperature of the substance.
Liquid B has a low critical temperature in comparison to all.
Liquid A,
Liquid A is left behind in the distillation flask.
This means liquid A has a high boiling point.
It can not vaporize easily.
Intermolecular forces of interaction between liquid A molecules are high.
High intermolecular forces of attraction between molecules mean a high critical temperature of the substance.
Liquid B has a high critical temperature in comparison to all.
Liquid C,
So, Liquid C would be having boiling point in between Liquid A and Liquid B.
The critical temperature of liquid C is in between liquid A and Liquid B.

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