KS3 · Chemistry

Distillation

Heat inky water gently and clear, colourless water drips out the far end, while the ink left behind gets darker. No magic: just two changes of state, in order.

Follow the water

1Heat gently23456

Stage 1 of 6: Heat gently. paused

Heat gently · 1/6drag to follow the water →

Inky water sits in a round-bottom flask. We warm it slowly and gently. Nothing dramatic yet.

Drag along the path to follow the water out of the inky mixture, one stage at a time.

Boiling points

Which one boils first?

A mixture of water and ethanol is slowly warmed up. Drag each liquid to where you think it boils. Water is probably the one you know. For ethanol, here's a clue: it boils at a lower temperature than water.

The kit

Distillation apparatus
gentle heatthermometerflaskcondenserdistillatecold water inwater out

Showing 2 layers: Apparatus, Cooling water

Layers

Explore

tap a part ↓

Cold water runs round the outside of the condenser's inner tube: in at the bottom, out at the top.

Tap a part to see its job. Switch the cooling water off and on to see where it runs.

Why gentle heat?

?

Reason it through

Why does heating the flask too strongly spoil the separation?

Link 1 of 4

First link · your turn

You turn the heat right up. What can happen to the temperature of the mixture?

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Locked — reveal the link above first
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Locked — reveal the link above first
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Locked — reveal the link above first

What do you think?

Getting the water back from salty water

You have a flask of salty water, and you want the water back out of it.

Which is closest to what you think right now?
How sure are you?

Going further

Simple distillationvsFractional distillation

Same idea, bigger job.

Focus

How many substances

Simple distillation

Two, e.g. salt and water, or ethanol and water

Fractional distillation

Three or more

The insight

Counting the substances in the mixture is a quick first check on which method you need.

Boiling points

Simple distillation

Works because the two boiling points are different

Fractional distillation

Can also separate substances with very similar boiling points

Extra apparatus

Simple distillation

No fractionating column

Fractional distillation

Uses a fractionating column

What you collect

Simple distillation

One distillate

Fractional distillation

Several distillates, each one called a fraction

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Boil it, then catch it: how to get a liquid back out of a mixture

What you need to know

  • Distillation separates and recovers a liquid from a solution or mixture. It's one of the simple ways of separating mixtures, alongside filtration, evaporation and chromatography.
  • It works because the parts of the mixture have different boiling points. As the mixture warms, the one with the lower boiling point boils first.
  • Boiling on its own would lose the gas into the air. Distillation keeps it by condensing it straight back into a liquid.
  • The two processes are boiling and condensation. Nothing melts, and the substance you collect is the same substance it was in the mixture.

The big picture

Distillation separates a liquid from a mixture and keeps it. The mixture is heated gently, the substance with the lower boiling point boils first, and a cold condenser turns that gas straight back into a liquid, which drips into another container as the distillate.

Key points

1Each pure substance has its own boiling point: water boils at 100 °C, ethanol at 78 °C.
2Heat slowly and gently, so only one substance boils and enters the condenser at a time.
3Thermometer bulb just below the side arm: it measures the temperature of the gas leaving the flask.
4Condenser: cold water in at the bottom, out at the top, never mixing with the gas. Keep it cold so the gas condenses before it can escape.
5The distillate is pure, or mostly pure. You can test its purity by checking its boiling point.
6Simple distillation separates two substances into one distillate. Fractional distillation uses a fractionating column for three or more substances, or very similar boiling points, and collects fractions.

Worked example

Problem

A mixture of ethanol and water is distilled with gentle heating. Which liquid collects in the container first, and how could you check whether that collected liquid is pure?

⚠ Watch out

Mixing up distillate and filtrate. The distillate is the liquid you collect by distillation; the filtrate is the liquid you collect by filtration.

🧠

Memory hook

Boil it, then catch it. B before C: Boiling gets it out, Condensing keeps it.

✓

Check yourself

Inky water is distilled. Without looking back, say what collects in the second container, what happens to the liquid left in the flask, and why the condenser is needed at all.

Flashcards

(14)
What does distillation do?
It separates and recovers a liquid from a solution or mixture.
Why can distillation separate a mixture?
Because the parts of the mixture have different boiling points.
A mixture of liquids is warmed up. Which one turns into a gas first?
The one with the lower boiling point.
Boiling points of water and ethanol?
Water: 100 °C. Ethanol: 78 °C.
The two processes in distillation
Boiling, then condensation. Nothing melts, and no substance changes identity.
Why not just boil the mixture in an open pan?
The gas mixes with the air and is lost. Distillation condenses it so it can be kept.
Job of the round-bottom flask
Holds the mixture and heats it evenly.
Where does the thermometer bulb go, and why?
Just below the side arm, to measure the temperature of the gas leaving the flask.
Which way does cooling water flow through a condenser?
In at the bottom, out at the top. It never mixes with the gas.
Why keep the condenser cold?
It speeds up condensation, so the gas turns to liquid before it leaves. A warm condenser lets more gas escape.
Distillate vs filtrate
Distillate: the liquid collected by distillation. Filtrate: the liquid collected by filtration.
Why heat gently?
So only one substance boils and enters the condenser at a time. Strong heating can make both boil and both get collected.
How can you test if a distillate is pure?
Check its boiling point.
Simple vs fractional distillation
Simple: two substances, one distillate. Fractional: three or more substances (or very similar boiling points), a fractionating column, and several fractions.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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How this lesson was checked. This KS3 Chemistrylesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 29 September 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.