Question

Define Azeotrope. What type of Azeotrope is formed by negative deviation from Raoult's law? Give an example.

Hint:

Azeotropes form when the vapor pressure of the mixture is either higher or lower than expected, preventing the components from separating by distillation. Negative deviations occur when stronger interactions exist between the molecules of the mixture.

Answer 1

1. Definition of Azeotrope:
An azeotrope is a mixture of two or more liquids that boil at a constant temperature and have a fixed composition, such that the vapor produced has the same composition as the liquid mixture. Azeotropes behave like pure substances during boiling and cannot be separated into their individual components by simple distillation.

2. Azeotrope formed by Negative Deviation from Raoult's Law:
When a mixture exhibits a negative deviation from Raoult's law, the intermolecular forces between the molecules of the two liquids are stronger than those in the individual components. As a result, the boiling point of the mixture is lower than that predicted by Raoult's law, and the vapor has a different composition than the liquid. This leads to the formation of a minimum boiling azeotrope.

Example:
An example of an azeotrope formed by a negative deviation from Raoult's law is the mixture of hydrochloric acid (HCl) and water. This mixture forms a minimum boiling azeotrope with a boiling point of 108°C and a composition of approximately 20% HCl and 80% water.