Question

What is Minimum Boiling Azeotropes? Give one example.

Answer 1

Azeotropes

• The solution or mixture having the same composition in liquid as well as in vapour phase and boils at a constant temperature is known as azeotropes. Due to constant composition, it can't be separated by fractional distillation.
• There are two types of azeotropes.
• (1)Minimum boiling azeotrope
• (2)Maximum boiling azeotrope

Minimum boiling Azeotropes

• Boiling of any ethanol-water mixture above 0% and below 95.6% mass will give a vapour of higher concentration of ethanol. Condensing and reboiling that mixture will finally lead to 95.6% ethanol.
• Reboiling further gives vapour and condensate of the same concentration, as graphically, this is where the liquid curve and the vapour curve meet. It is impossible to obtain pure ethanol from this mixture. It boils as a pure liquid with a constant boiling point.
• This is an azeotropic mixture or a constant boiling mixture.

Hence, minimum boiling azeotropes deviate much more positively from Raoult’s law at a specific composition. They possess a positive deviation.

Example

• The mixture of ethanol and water is one example of minimum boiling Azeotropes.
• On fractional distillation, the solution contains roughly 95% ethanol by volume.