Question

The system that forms maximum boiling azeotrope is: -
(a)- acetone - chloroform
(b)- ethanol - acetone
(c)- n-hexane – n-heptane
(d)- carbon disulfide – acetone.

Answer 1

Hint: First we have to check that the mixture is ideal or non-ideal. Maximum boiling azeotropes show a negative deviation. They have delta volume and evolution of heat negative.

Complete answer:
Let us understand azeotropes:
In the case of a solution showing a positive deviation from Raoult’s law, at one of the intermediate compositions, the total vapor pressure is the highest and the boiling point is the lowest. In the case of solutions showing negative deviations from Raoult’s law, for one intermediate composition, the vapor pressure is the lowest, and the boiling point is the highest.

For liquid pairs of such intermediate compositions, the composition of the liquid and vapor phase is the same. So, when a liquid mixture of such a composition vaporizes without a change in composition, the liquid obtained by the condensation of the vapor also has the same composition i.e. the mixture distills over as if it were a pure liquid. The composition of the mixture is fixed.
This type of liquid mixture, having a definite composition, and boiling like a pure liquid, is called a constant boiling mixture or it is called azeotrope.
In the case of positive deviation, we get minimum boiling azeotropes and in case of negative deviation, we get maximum boiling azeotropes.
In minimum boiling azeotropes, the boiling point of the azeotrope is less than the boiling point of either pure components. In maximum boiling azeotropes, the boiling point of the azeotrope is more than the boiling point of either pure component.

Let us see all the options one by one:
(a)- acetone – chloroform: It is a non-ideal solution and has a negative deviation. It is a maximum boiling azeotrope.
(b)- ethanol – acetone: It is a non-ideal solution and has a positive deviation. It is a minimum boiling azeotrope.
(c)- n-hexane – n-heptane: It is an ideal solution and doesn't show any deviation.
(d)- carbon disulfide – acetone: It is a non-ideal solution and has a positive deviation. It is a minimum boiling azeotrope.

So, the correct answer is “Option A”.

Note: There is no such process for knowing whether the compound is ideal or non-ideal, we have to learn the examples of each. Solutions showing positive deviations the interaction between the components are less than in the pure state and in negative deviation, the interaction between the components is greater than the pure components.