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. Azeotrope Definition:
An azeotrope is a liquid mixture of two or more components that boils at a constant temperature with a fixed composition. The vapor produced has the same composition as the liquid. Azeotropes act like pure substances during boiling and resist separation by simple distillation.

2. Azeotropes and Negative Deviation from Raoult's Law:
Negative deviations from Raoult's law occur when intermolecular forces within the mixture are stronger than those of the pure components. This results in a boiling point lower than predicted by Raoult's law, and a vapor composition different from the liquid, leading to a minimum boiling azeotrope.

Example:
A minimum boiling azeotrope formed by negative deviation from Raoult's law is the mixture of hydrochloric acid (HCl) and water. This mixture boils at 108°C and consists of approximately 20% HCl and 80% water.