Q.You have a mixture of three liquids A, B and C. There is a large difference in the boiling points of A and rest of the two liquids i.e., B and C. Boiling point of liquids B and C are quite close. Liquid A boils at a higher temperature than B and C and boiling point of B is lower than C. How will you separate the components of the mixture. Draw a diagram showing set up of the apparatus for the process.

The key idea is Separation Techniques — using differences in boiling points to separate a mixture of miscible liquids.

Reasoning:

1. Since A has a much higher boiling point than B and C, it can be separated first by simple distillation — heat the mixture; B and C distil over, leaving A behind.
2. B and C have close boiling points, so they cannot be separated by simple distillation. Use fractional distillation with a fractionating column to separate them, as B has the lower boiling point and distils first.

Diagram: …

The problem gives you three liquids with a clear hierarchy in boiling points: A boils much higher than B and C, while B and C have boiling points very close together, with B lower than C. This tells you exactly which separation technique to apply at each stage.

Why distillation works here: Distillation exploits differences in boiling points. When you heat a mixture, the component with the lowest boiling point vaporises first. By condensing that vapor, you collect it as a pure liquid. The larger the boiling-point gap, the easier the separation.

1. First step — Separate A from the mixture using simple distillation

   Since A boils at a temperature much higher than both B and C, heating the mixture gently will cause B and C to vaporise together, leaving A behind in the distillation flask. The vapor of B and C passes through the condenser, where it cools and turns back into liquid — collected as a mixture of B and C in the receiver.

   What remains in the flask is pure liquid A. This is simple distillation: one evaporation-condensation cycle is enough because the boiling-point difference is large (typically > 25–30°C).

2. Second step — Separate B and C using fractional distillation

   Now you have a mixture of B and C, whose boiling points are quite close. Simple distillation won't work well here — you'd get impure fractions. Instead, use fractional distillation.

   The apparatus includes a fractionating column (a long tube packed with glass beads or inert material) placed between the distillation flask and the condenser. As the vapor rises through the column, it repeatedly condenses and re-evaporates. Each cycle enriches the vapor in the more volatile component (B, which has the lower boiling point).

   Eventually, pure B vapor reaches the top of the column first and is condensed and collected. After B is fully collected, the temperature rises, and then pure C vapor reaches the top and is collected separately.

3. Draw the apparatus Below is a description of the setup for the entire process. You would draw two separate setups, but the key diagram is for the fractional distillation step (the more interesting one). …