Question

How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25° C) which are miscible with each other?

Answer 1

The components of a mixture containing two miscible liquids i.e.; kerosene and petrol can be separated by distillation as it is given that the difference in their boiling points is $25°\mathrm{C}$.

• Boiling point of kerosene is approximately $150–180°\mathrm{C}$
• Boiling point of petrol is $95°\mathrm{C}$.

Miscible liquids: A mixture of two or more liquids which intermix with each other to form a homogeneous solution. Example: mixture of ethanol and water

Distillation: It is a technique for separation of a mixture of two miscible liquids which boil without decomposing (as that will change the substance to be separated) and have sufficient difference in the boiling points (i.e.; more than 25 K)

Principle involved in the separation of mixture:

• The component with lower boiling point evaporates first and leaves the mixture due to the sufficient difference in their boiling points.

Set-up for the distillation:

• Mixture of kerosene and petrol is poured into a round bottom flask held by a clamp and placed on the water bath on a burner.
• The mouth of the round bottom flask is fitted with a thermometer and a water condenser called Liebig's condenser.
• The inner of the condenser is connected to the flask for the liquid to pass through and cool water is circulated through its outer tube to condense the vapours coming from the round bottom flask.
• An empty measuring cylinder is placed at the other end of the condenser to collect the liquid.

Process of distillation:

• The mixture is heated gradually.
• Petrol begins to form vapours as the boiling point of petrol is attained first.
• The vapours of petrol condense when passed through the condenser and are collected in the measuring flask.
• Kerosene remains behind in the round bottom flask as it has a higher boiling point.