Simple Distillation – IGCSE Chemistry Definition

Simple distillation is a fundamental separation technique tested on Paper 6 (practical) and Paper 2/4 (theory). Candidates must know the apparatus, the method, and when to choose simple distillation over other techniques.

The 0620 definition

Simple distillation is a technique for separating a liquid from a solution by evaporating the liquid and then condensing the vapour back to a liquid, which is collected separately.

It is used to separate a solvent from a dissolved solute, or to separate two liquids with very different boiling points.

The apparatus

• Round-bottomed flask containing the solution (held by clamp stand)
• Thermometer in the neck of the flask (measures boiling point of vapour)
• Condenser (Liebig condenser: cold water in outer jacket, vapour in inner tube)
• Collection flask/beaker for the distillate
• Heat source (Bunsen burner or electric heater)

The method

1. Heat the solution in the flask
2. The solvent with the lower boiling point evaporates first
3. Vapour travels into the condenser
4. Cold water in the condenser cools the vapour, condensing it back to liquid
5. The pure liquid (distillate) drips into the collection flask
6. The solute remains in the original flask (it does not evaporate)

Example: obtaining pure water from salt solution

• The solution is heated; water evaporates at 100 °C
• Water vapour condenses in the condenser
• Pure water is collected as the distillate
• Sodium chloride remains in the flask (its boiling point is 1413 °C — it does not evaporate)

Simple distillation vs evaporation

If you want…	Use…
The dissolved solid (salt)	Evaporation / crystallisation
The pure liquid (water)	Simple distillation

Worked exam question

A student wants to obtain pure water from seawater. (a) Name a suitable separation technique. [1] (b) State the purpose of the condenser. [1] (c) Explain why the water collected is pure but the original seawater is not. [1]

Mark scheme

(a) (Simple) distillation [1]

(b) To cool the water vapour / condense the steam back to liquid water [1]

(c) Only water evaporates; the dissolved salts remain in the flask / salts have much higher boiling points so they do not evaporate [1]

Common exam mistakes

• Confusing simple distillation with fractional distillation — simple distillation does not use a fractionating column.
• Drawing the condenser with water flowing in the wrong direction — cold water should enter at the bottom and exit at the top for maximum cooling efficiency.
• Saying distillation “filters” the salt out — distillation separates by boiling point, not by particle size.