Question

Explain how fractional distillation is used to separate mixtures.

Answer 1

Definition of fractional distillation.

• Fractional distillation is the process in which two or more miscible liquids with different boiling points are separated by the process of distillation
• .Liquids that mix each other are called miscible liquids.
• The mixtures are distilled and the various liquids separate out at their respective boiling points.
• This is useful only if the difference in boiling point is less than 25⁰C.
• Some of the mixtures that can be separated by fractional distillation are water and alcohol, mixtures of alcohol, Chloroform and water etc.
• Petroleum products are also separated by fractional distillation.

Fractional distillation of water and alcohol.

• In a mixture of water and ethanol boils at 78.4⁰C while the water boils at 100⁰C
• If the mixture is gently heated, the more volatile component, alcohol will concentrate to a greater degree in the vapour leaving the liquid, water.
• The mixture is put into the distillation flask. A fractionating column and a thermometer are fitted.
• The side tube of the distillation flask is connected to Liebig's condenser.
• The inlet tube of the condenser is connected to a water source the mixture boils, vapour rises up the column.
• The vapour of water condenses and flows back into the distillation flask while vapours of ethanol continue up.
• The vapours at the top of the column then pass into the Liebig's condenser, which cools it down until it liquefies and flows into the receiving flask as distillate. water is left behind in the flask in the distillation flask. The two miscible liquids can be effectively separated.