How does non-ideal solution affect the process of distillation?Watch
Can you also explain the overall application of Raoult's law in distillation?
This leads to a straight line on a graph for total vapour pressure against % composion of the two components.
Non-ideality is caused by interaction between the particles of each component which creates deviation from Raoult's law and the vapour pressure/composition straight line becomes curved, either up or down, depending on the type of interparticular interactions.
This may create a maximum in the vapour pressure curve, which prevents separation of the two components by fractional distillation, as the % composition at this point will have a boiling point minimum and produce a constant boiling mixture called an azeotrope.
One example of this occurs in mixtures of ethanol and water, where the azeotrope has 95.63% ethanol and 4.37% water. This mixture boils at 78.2ºC under atmospheric pressure and produces a vapour with exactly the same compostion, meaning that fractional distillation cannot separate it.