Question

Which of the following azeotropic solutions has the boiling point less than the boiling point of the constituent compounds?
(A) ${\text{CHC}}{{\text{l}}_{\text{3}}}$ and ${\text{C}}{{\text{H}}_{\text{3}}}{\text{COC}}{{\text{H}}_{\text{3}}}$
(B) Phenol and aniline
(C) ${\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{OH}}$ and ${\text{C}}{{\text{H}}_{\text{3}}}{\text{COC}}{{\text{H}}_{\text{3}}}$
(D) ${\text{CHC}}{{\text{l}}_{\text{3}}}$ and Benzene

Answer 1

To answer this question, you must recall Raoult's Law and the concept of azeotropic solutions. An azeotropic solution is that solution which is composed of two liquids and has constant composition in the liquid and vapour phase. In other words, azeotropic solutions vaporize and condense together. Thus, they cannot be separated using the process of distillation. Azeotropic solutions generally show deviation from the Raoult’s law which can be either positive deviation or negative deviation.

Complete step by step solution
We know that Raoult's law states that the vapour pressure of a solution containing a volatile solvent and a non- volatile solute is directly proportional to the mole fraction of the volatile solvent. An ideal solution follows the Raoult’s law while a real solution shows deviation from the Raoult’s law. The deviations can be of two types namely positive deviation and negative deviation.
The boiling point of an azeotropic solution is less than that of its constituent compounds when the interactions between the solvent and solute are weaker than the solvent- solvent and solute- solute interactions. As a result, the bonds in the solution are broken easily and hence vaporization is easier. Such a solution is said to show positive deviation.
Of the given solutions, the solution of ethanol and acetone shows positive deviation.
The correct answer is (C).

Note
When the interactions between the solvent and solute are greater than the individual solvent- solvent and solute- solute interactions, the solution is said to show negative deviation from Raoult’s law.