Fractional Distillation: Principle, Procedure & Applications

Fractional distillation is a type of distillation process that is used to separate two or more miscible liquids from the mixture. Fractional distillation involves the repetition of condensation and distillation processes.

• By fractional distillation process, the mixture of liquids is separated into component parts.
• The liquids in the mixture start separating when the mixture is heated at a temperature where liquids start vaporizing. 
• The basic principle of fractional distillation is that liquids of the mixture boil and evaporate at different temperatures. 
• The fractional distillation method is used in the chemical and petroleum industry to purify chemicals and separate mixtures to get their components.
• Two or more miscible liquids can be separated through fractional distillation if the difference between their boiling point is less than 25 K (-248 ^oC).

Read More: NCERT Solutions for Class 9 Science Chapter 2: Is Matter Around Us Pure

Key Terms: Fractional Distillation, Miscible Liquids, Vapours, Temperature, Evaporation, Condensation, Boiling Point

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Principle of Fractional Distillation

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When the mixture of liquid is heated, then liquid having a lower boiling point boils first and converts into vapours. The vapour composition of a mixture does not remain equivalent to the liquid composition. On heating the mixture, liquids start boiling and change to vapour form.

• In a vapour state, more volatile components stay longer than the liquid component.
• Distillation and condensation are used and the liquid mixture is separated into components.
• After heating, the more volatile components increase in a vapour state. Also when this vapour is liquefied, the volatile component increases in the liquid state.
• Distillation is the process of vaporization then followed by liquefaction (condensation).
• On repetition of the distillation process, the more volatile fractions of the mixture stay in the pure state in the liquid state. 
• Fractional distillation separates the mixture into a pure substance.

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Fractional Distillation: Procedure

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The procedure is as follows:

1. Fractional distillation apparatus such as a distillation flask, fractionating column, receiver, condenser, thermometer, water condenser, and heat source.
2. The fractionating column is a tube packed with glass beads. It is placed in between the water condenser and the distillation flask (as shown below). These beads of fractionating column act as a surface for vapours to cool and liquefy repeatedly. 

Fractional distillation

3. As the apparatus is set, a mixture containing two miscible liquids A and B is taken. Liquid A is more volatile than B.
4. After that, the mixture is added to the distillation flask, and the fractionating column is attached to the tip of the flask.
5. The applied heat increases the temperature of a mixture. As the mixture starts boiling, the vapour starts rising in the flask. These vapours are obtained from the volatile fractions of liquid A.
6. Then, vapours move through the fractionating column into the condenser. In a condenser, the vapour cools to form a liquid which is then stored in the receiver.
7. Until the complete separation of two liquids vaporization and condensation takes place continuously throughout the distillation process. 

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Applications of Fractional Distillation 

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The applications of fractional distillation are:

• Fractional distillation is used in the separation of miscible liquids. For example separating benzene and chloroform, water and acetone.
• Fractional distillation is used in the process of water purification. 
• It is used for the production of high-quality and pure silicon from dichlorosilane. This extracted silicon is used in semiconductors. 
• Fractional distillation is used in the separation of liquefied air. Components like concentrated oxygen and argon and liquid nitrogen are obtained. 
• Used in the preparation of alcohol which is used as a pharmaceutical substance.
• It is used in various industries such as chemical plants and oil refineries for the separation and purification of many chemical compounds. 

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Things to Remember

• The basic principle of fractional distillation is that various liquids boil at different temperatures.
• Fractional distillation is used to separate two or more liquids whose boiling point difference is less than 25 K. 
• In fractional distillation, the liquid in the mixture with a lower boiling point starts boiling first and evaporates.
• In fractional distillation, evaporation, condensation, and collection of vapour are repeated to separate liquids.
• In refineries, fractional distillation is used to purify chemicals and separate impurities to get their components.
• Fractional distillation is used in the process of water purification. 

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Previous Year Questions

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