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Fractional distillation
Fractional distillation is used for the separation of a mixture of two or more miscible liquids
for which the difference in boiling points is less than 25 Kelvin. The apparatus for
fractional distillation is similar to that of simple distillation, except that a fractionating
column is fitted in between the distilling head and the RB flask.
Materials Required:
Mixture of ethanol and water, 250ml and 100 ml RB flasks, Stand with clamp, Fractionating
column, Distilling head, Porcelain chips, Thermometer adapter, Water condenser, Vacuum
adapter and heating mantle.
Procedure:
Take a mixture of ethanol and water and pour it into a 250 ml RB flask.
Take some porcelain chips and put it into the mixture.
Now connect a fractionating column to the RB flask and clamp it.
Connect a distilling head to the fractionating column and a thermometer adapter containing
thermometer to the distilling head. Connect a water condenser to the outlet of
the distilling head and clamp it. Now connect a vacuum adapter to the water
condenser and a 100 ml RB flask to the vacuum adapter.
Clamp the RB flask and place it in a beaker containing water.
Now connect a rubber tube between the inlet of the condenser and the tap to allow the
cold water to enter. Connect another rubber tube to the outlet
of the condenser to pour the hot water from the condenser to the sink.
Open the tap so that water flows through the tube and fills the condenser and then comes
out through the outlet. Set the temperature of the heating mantle
and heat the contents of the RB flask. At 78°Celsius, ethanol vaporises and the
vapours rise through the fractionating column and pass through the condenser and condensation
takes place and ethanol gets collected in the receiver flask in the liquid form and
water is left behind in the distillation flask. Therefore the separation of two or more miscible
liquids for which the difference in boiling points is less than 25 Kelvin can be done
only by Fractional distillation. Since ethanol & water forms an azeotrope,
the distillation has to be repeated to obtain the pure components.