Distillation

Distillation Distillation can be defined as a process in which a liquid or vapor mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat. Distillation is based on the fact that the vapor of a boiling mixture will be richer in the components that have lower boiling points. Therefore, when this vapor is cooled and condensed, the condensate will contain more volatile components. At the same time, the original mixture will contain more of the less volatile material. Mixtures of liquids whose boiling points are similar (separated by less than 70°C) cannot be separated by a single simple distillation. In these situations, a fractional distillation is used. Vacuum distillation is distillation at a reduced pressure. Since the boiling point of a compound is lower at a lower external pressure, the compound will not have to be heated to as high a temperature in order for it to boil. Vacuum distillation is used to distill compounds that have a high boiling point or any compound which might undergo decomposition on heating at atmospheric pressure. The vacuum is provided either by a water aspirator or by a mechanical pump. Azeotropes Azeotrope is a mixture of two liquids which show positive of Raults law and mixture solution will boil at lower temperature than either of the two components. Such mixtures are called azeotropes. Azeotropes cannot be separated by distillation; e.g. a mixture of 5% water and 95% ethanol make an azeotrope. Azeotropes can also be formed when the mixture boils at higher temperature than either of the components.