Distillation and Fractional Distillation
These methods are used to separate mixture of miscible liquids
What is Distillation?
It is the process of heating and cooling a mixture
It is used to separate 2 substances having different boiling points
It is used to separate mixture of acetone (nail paint remover) and water
Steps to Separate a Mixture of Acetone and Water by Distillation
Mixture of Acetone and Water
Thermometer to Monitor Temperature
- Take a mixture of Acetone and Water in a flask
- Heat it
- Monitor the temperature with help of Thermometer
- When boiling point of acetone is reached, it converts into vapour
However, water is left in flask as it has higher boiling point
(Boiling Point of Acetone is 56 degree celsius but Water is 100 degree celsius)
- These vapours of acetone flow into the condenser where it gets cooled and converts into liquid again
- This liquid acetone is stored in the beaker while water continues to remain in the flask
Hence, we are able to separate mixture of acetone and water
When is Distillation Used?
It is used when:
- Liquids do not decompose on heating
(Water and Acetone do not decompose on heating)
- Sufficient Difference in Boiling Points of both liquids
(It is used to separate mixture of acetone and water as Boiling Point of Acetone is 56 degree celsius but Water is 100 degree celsius)
This method cannot be used when there is less difference in boiling point of different components.
Difference in boiling point should be atleast 25 O C(or K) to use this method.
If the difference in boiling point is less that 25OC then,Fractional Distillation is used
What is Fractional Distillation?
It is a process used to separate 2 miscible liquids having closer boiling points
Difference between the boiling points of liquids is less than 25 K
The process is similar to distillation in which liquids are first heated and cooled
However in this case, fractionating column is also used
What is a fractionating column?
It is a tube packed with glass beads
These beads provide
surface for the vapours to cool and condense repeatedly.
Mixture is heated in a flask
(Different components of mixture have different boiling points)
- When the component of mixture with lower boiling point reaches its boiling point, it converts from liquid to vapour phase.
- This vapour is cooled and collected in the receiver to obtain liquid in pure form separate from mixture.
- The second component also starts to convert to vapours but is condensed by the fractionating column and it trickles down back into the flask.
- However once all of the first component is collected in the receiver, the temperature starts rising.
- At this point the receiver is changed and the second liquid is collected.
Hence the two liquids can be separated using fractional distillation
It is used to separate different gases in air, petroleum products etc.