Question

An azeotropic solution of two liquids has boiling point lower than either of them when it

• A. Shows negative deviation from Raoult’s law
• B. Shows no deviation from Raoult’s law.
• C. Shows positive deviation from Raoult’s law.
• D. Is saturated

Answer 1

The correct option is C Shows positive deviation from Raoult’s law.

Azeotropic mixtures are also known as constant boiling mixtures. They are liquid mixtures which boil over without any change in the composition. Such mixtures cannot be separated into components by fractional distillation. They are of two types: maximum boiling azeotropes and minimum boiling azeotropes.
Maximum boiling azeotropes are formed by solutions having negative deviations. Boiling point is maximum.
For example,
• Water and HCl
• Water and nitric acid
• Chloride form and acetone
• Acetic acid and pyridine
Minimum boiling azeotropes are formed by solutions having positive deviations. Boiling point is minimum. For example,
• Acetic acid and toluene
• Pyridine and water
• Ethanol and benzene
• Water and ethanol