Question

Fractional distillation is suitable for the separation of miscible liquids with a boiling point difference of about 25 K or less. What part of the fractional distillation apparatus makes it efficient and possesses an advantage over a simple distillation process. Explain using a diagram.

Answer 1

Simple distillation;

1. Simple distillation is a method of separating mixtures in a boiling liquid mixture based on differences in their volatilities.
2. By the application of heat, the components in a sample mixture are vaporized and then immediately cooled by the action of cold water in a condenser.
3. For example, water can be separated from the salt solution by the process of simple distillation, since the water has a very much lower boiling point than salt.
4. When the salt solution is heated, the water evaporates, then cooled and condensed into a separate container.
5. The salt does not get evaporated and so it stays behind.
6. This method is only effective for mixtures that are having a minimum difference of $25°C$ in the boiling point.

Fractional distillation;

1. Fractional distillation is a type of distillation in which the miscible liquids get separated.
2. The mixture of liquids that have a small difference in the boiling point undergoes fractional distillation for the separation process.
3. The mixture can be separated into component parts by repeated distillations and condensations and the purity of the distillate improves with every cycle.
4. The fractional column, provided with glass beads in it is the most important part of the fractional distillation apparatus.
5. The fractional column helps to prevent the upward movement of the vapours of the two liquids.
6. When the liquid is heated in the round bottom flask, the vapours of the liquid mixture rise into the fractionating column.
7. The vapours then enter into the condensation chamber also known as a condenser and then are cooled and condensed on the wall of the condenser.
8. Now the hot vapours that are emerging from the distillation flux heat the condensed vapours creating new vapours.

Advantages of fractional distillation over a simple distillation process are;

• A fractionating column makes the process of fractional distillation more efficient than the process of simple distillation because the glass beads in the fractionating column by providing increased possibilities for condensation of the liquid.
• Simple distillation will only have one vaporization-condensation cycle in the whole process, while the fractional cycle will have at least two cycles, and the purity of the distillate is also gets improved with every cycle.
• Simple distillation separates liquids with boiling point gaps of at least $25°C$ whereas fractional distillation separates liquids with closer boiling points

Therefore, the fractional column provided with glass beads makes the process of fractional distillation more efficient than the process of simple distillation.