Question

Name a method to check the purity of liquid.

Answer 1

1. A pure liquid has a fixed melting point or boiling point at constant pressure.
2. The purity of a liquid can be tested by checking its melting point or boiling point.
3. If a substance is impure i.e. it contains traces of another substance, the melting and boiling point of that substance will get changed.

Distillation:

1. Distillation is defined as the selective boiling and subsequent condensation of a component in a liquid mixture.
2. It is a separation technique that can be used to either increase the concentration of a particular component in the mixture or to obtain (almost) pure components from the mixture.
3. In this process, the liquid is heated to its boiling point so that it is converted into vapors.
4. On cooling the vapors, the pure liquid is obtained and collected separately.
5. The whole component having a low boiling point is collected in the receiver and the other component having a high boiling point remains in the flask.
6. Example - a mixture of acetone (boiling point $56°\mathrm{C}$) and water (boiling point $100°\mathrm{C}$), purification of alcohol, and crude oil refining.

Hence, simple distillation is the method that can be used to check the purity of liquid.