Upper secondary · 15 min

Simple distillation: separating ethanol and water

Heat a coloured ethanol–water mixture and collect condensed vapour. Relate vapour enrichment to volatility and learn why simple distillation cannot remove the ethanol–water azeotrope.

Goal

Use boiling-point differences to separate volatile components and interpret temperature changes during distillation.

Apparatus and reagents

Ethanol–water mixture, distillation flask and thermometer, condenser with water tubing, receiving flask, boiling chips, heating mantle or hot-water bath, goggles.

Procedure

Inspect the simulated flask, thermometer, condenser and receiver; note the starting temperature.
Raise the temperature gradually and observe when boiling and the first drops of distillate appear.
Increase the collected-volume control and compare the receiver level with the flask temperature; discuss the change in vapour composition.
Explain why the early distillate is richer in ethanol and identify the constant-boiling azeotrope as a limit to purification by ordinary distillation.

What to observe

Below the boiling region only occasional bubbles form; once boiling starts, condensate drips steadily into the receiver.
The distillate is lighter coloured than the flask contents: the vapour is enriched in the more volatile ethanol.

Explanation

Ethanol boils at 78.4 °C and water at 100 °C, so the vapour — and the early distillate — is richer in ethanol. The temperature plateau near the azeotrope (≈ 78.2 °C, ~95.6 wt % ethanol) is the limit of simple distillation; breaking it needs a different technique.

History of the experiment

Distillation goes back to Alexandrian stills of the first centuries CE, but Jabir ibn Hayyan's treatises around 800 CE turned the alembic into a systematic laboratory instrument for purifying substances. Medieval distillers chasing alcohol perfected the coiled condenser, and the same apparatus — pot, condenser, receiver — purifies solvents and fractions petroleum today. The vapour-recompression logic hasn't changed in twelve centuries.

Chemists behind it

Jabir ibn Hayyan (Geber)