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

Example

It is used to separate mixture of acetone (nail paint remover) and water

Steps to Separate a Mixture of Acetone and Water by Distillation

Equipments Required:

• Mixture of Acetone and Water
• Distillation Flask
• Thermometer to Monitor Temperature
• Condenser
• Beaker

Steps:

1. Take a mixture of Acetone and Water in a flask
2. Heat it
3. Monitor the temperature with help of Thermometer
4. 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)
5. These vapours of acetone flow into the condenser where it gets cooled and converts into liquid again
6. 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

Note

This method cannot be used when there is less difference in boiling point of different components. 

Difference in boiling point should be atleast 25° C to use this method.

If the difference in boiling point is less that 25° C 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.

Process

• 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

Uses of Fractional Distillation

It is used to separate different gases in air, petroleum products etc.