Azeotrope

As a result of the very strong deviation from Raoult's law, we will have a situation called Azeotrope.

The word actually comes from greek and has a literal meaning of boiling remains unchanged.

In other words azeotrope is actually a mixture of two liquids or more that has a constant boiling temperature either lower or higher than the boiling point of pure components.

The composition at which this situation is observed is called azeotropic composition.

It is a bit problematic to deal with as the mixture can no longer be separated to their pure components with the help of distillation. No matter how you do or perform the distillation, you will end up having that azeotropic composition. It is also worth mentioning this is the composition at which the liquid phase and vapour phase both have the same composition.

Example:  

A mixture of Ethanol and Water is the most classical example of a mixture that has an azeotropic composition at around 95 weight percent of Ethanol and 5% water.

Boiling point of pure water 100° C

Boiling point of pure ethanol 78.5°C

At this composition the mixture has a boiling temperature of 78,2°C.

This is lower than the boiling points mentioned above.

Next entry will deal with two different types of Azeotropes in detail.