Boil it, cool it, collect it

The idea

Distillation separates two miscible liquids, or a liquid from dissolved solids, by heating until the lower-boiling liquid vaporises, then cooling the vapour in a condenser so it is collected separately as a pure liquid.

A mix-up in the lab

A student accidentally mixes acetone and water. They mix completely. Letting the mixture evaporate would lose both liquids into the air.

How could you get both liquids back, separately?

• Heat until one boils off, then cool its vapour back to liquid
• Filter it through paper
• Wait for the water to turn into acetone

Run a distillation

Heat the flask to a temperature between the two boiling points. Then keep heating.

Distillation

Distillation separates a homogeneous mixture of two miscible liquids by heating until the liquid with the lower boiling point vaporises. The vapour is cooled in a condenser and condenses back into a pure liquid collected in a separate vessel. The other liquid, or any dissolved solid, remains in the flask.

Acetone boils at about 56 °C and water at 100 °C, so they can be separated. Distillation also recovers the solvent or separates a liquid from a solution containing dissolved solids.

Kannauj. The earthy smell after the first rain is captured as *mitti ka ittar* by the traditional Deg-Bhapka distillation method. Distillation is also used to extract fragrances from flowers.

Notes

Distillation: heat until the lower-boiling liquid vaporises, condense the vapour, and collect it as a pure liquid. The rest stays in the flask.

Check yourself

In distillation, the vapour of the lower-boiling liquid is…

Acetone boils at about 56 °C and water at 100 °C. Which stays in the flask when you heat to 70 °C?

What does the condenser do?

Which job can distillation do?

• let out into the air. Then it would be lost.
• cooled in a condenser and collected as a pure liquid — correct. Yes.
• heated until it turns into a solid. It is cooled back into a liquid.
• Water — correct. Yes. Acetone vaporises first.
• Acetone. Acetone boils at the lower temperature, so it leaves first.
• Both. Only acetone has reached its boiling point.
• Heats the mixture. The heater does that.
• Cools the vapour so it turns back into a liquid — correct. Yes.
• Filters out solids. Filtration is a different method.
• Make a solid dissolve faster. Not what distillation does.
• Turn a colloid into a suspension. Not what distillation does.
• Get a liquid out of a solution containing dissolved solids — correct. Yes.