Question

What is meant by positive deviation from Raoult's law? Give an example. What type of azeotrope is formed by positive deviation?

Hint:

Positive deviation from Raoult's law results in a mixture with higher vapor pressure, and such mixtures often form azeotropes that cannot be separated by distillation.

Answer 1

Positive deviation from Raoult's law occurs when the vapor pressure of the solution is higher than predicted by Raoult's law. This happens when the intermolecular forces between the different components of the solution are weaker than the forces in the pure components. An example of this is the mixture of ethanol and water, where ethanol has weaker interactions with water molecules, leading to a higher vapor pressure. Azeotropes formed by positive deviation show a constant boiling point that is lower than the boiling point of each pure component.