Question

Various methods for the purification of organic compounds are based on the nature of

the compound and the impurity present in it. Explain the principle involved in the

following methods of purification:

a) Distillation b) Steam distillation​

Answer 1

Answer:

Distillation

The underlying principle behind distillation is that the mixture of liquids can be separated by the difference in their boiling points. The boiling point is defined as that temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure. This method separates volatile liquids from non-volatile liquids

The mixture is taken in the RB flask and boiled. The more volatile or the component with lower boiling point evaporates faster and is collected in a separate container. A condenser is used to hasten the process of condensation.

For example, a mixture of chloroform and aniline can be separated by distillation. The boiling point of chloroform is 60°C and that of aniline is 189°C. Therefore distillation can be used to separate a mixture of chloroform and aniline.

Steam Distillation

In this variant, steam is passed into the flask containing the liquids to be separated. The principle here is that the liquids will boil faster because of aqueous tension (vapor pressure of water) helps in equalizing the atmospheric pressure.

Total pressure = Aqueous tension + vapor pressure of liquid components

In the absence of aqueous tension, the process of boiling would have been continued until it equalizes the atmospheric pressure. Now with the addition of steam, that process is expedited.