Distillation collects a liquid by boiling and condensing it; chromatography separates dissolved substances such as dyes. Explain each principle and when distillation beats evaporation.
Ships at sea make fresh water by boiling seawater and catching the steam. Forensic scientists find out which pen wrote a note by letting water creep up a strip of paper.
Two more techniques. Distillation uses the same property as evaporation (boiling point) but keeps the vapour. Chromatography separates substances that are all dissolved.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Practise: A few on your own, to check you have it.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: fresh water from seawater
ExploreTry it on the board and compare what happens with your prediction.
Explore: run both techniques
Blue: water particles. Orange: salt particles.
Ink spots from a note and two black pens sit on a pencil line. The bottom of the paper is dipped in water.
Try it yourselfNothing is saved: start again as often as you like.
Distil the seawater until the first flask is dry.
Use the board. This ticks when you get there.
Run the chromatography.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: distillation is not just evaporation
In your book: explain the principle of each technique and name a mixture each one suits.
Both techniques heat a liquid until it turns to gas. Sort each statement.
Uses the difference in boiling pointThe liquid boils far below the dissolved solid.
Needs heat
The vapour escapes into the air
The vapour is cooled and collected as a liquidThis is the key difference.
You end up with only the solid
You end up with the liquid and the solid
Needs a condenser and a collecting flaskExtra equipment to catch the vapour.
Match each job to the technique that suits it.
Get drinking water from seawater
Get salt from seawater, letting the water go
Find out which dyes are in a black ink
Get sand out of sandy water
PractiseA few on your own, to check you have it.
Mix it up
Elaborate TypicalUse the same idea in a new context.
Elaborate: distillation or evaporation?
Both use the same property. Which would you choose?
A salt farm wants salt from seawater.Only the salt is wanted. Sun and wind do it for free.
A ship needs drinking water from seawater.The water is what's wanted, so the vapour must be collected.
A lab wants very pure water with nothing dissolved in it.Distilled water leaves every dissolved substance behind.
You want sugar crystals from sugar syrup.Only the sugar is wanted.
You want to keep both the water and the salt from a salt solution.Distillation collects the water and leaves the salt.
Elaborate WiderUse the same idea in a new context.
Elaborate: three techniques, three properties
Which property does each technique use?
Crystallisation: a hot, concentrated solution is left to cool, and crystals form.Less solid can stay dissolved as the solution cools, so it comes out as crystals.
Chromatography: food colourings separate on paper.Each colouring travels a different distance.
Distillation: alcohol is separated from water.Alcohol boils at about 78 °C, water at 100 °C.
Elaborate WiderUse the same idea in a new context.
Elaborate: First Nations knowledge and plant oils
The Bundjalung people of northern New South Wales have long used the leaves of the tea tree, crushing them or soaking them in water to use as medicine. Today tea tree oil is extracted by steam distillation.
Which property or process does each step use?
Crushing tea tree leaves
Soaking crushed leaves in water
Modern steam distillation: steam passes through the leaves
Modern steam distillation: separating the collected liquidThe oil is drawn off the top of the condensed water.
Elaborate WiderUse the same idea in a new context.
Elaborate: reading a chromatogram
Chemists compare spots with the Rf value: the distance the spot moved divided by the distance the water moved, both measured from the pencil line. In the Pen A lane, the water moved 10.0 cm.
The blue spot moved 8.0 cm. What is its Rf value?
The red spot moved 5.0 cm. What is its Rf value?
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
What did you think would collect in the second flask? Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Distillation separates a liquid from what is dissolved in it by boiling the liquid and cooling the vapour back into a liquid somewhere else.
Evaporation and distillation use the same property (boiling point), but distillation collects the vapour and evaporation lets it escape.
Chromatography separates a mixture of dissolved substances, such as dyes, because each is carried a different distance.
Distillation suits seawater (to get water). Chromatography suits inks, food colourings and plant pigments.
For teachers
Students describe the principles of distillation and chromatography, identify a mixture for each, and explain when distillation is chosen over evaporation (AC9S7U06, node 4). About 25 minutes.
I can describe the principle of distillation and of chromatography.
I can name a mixture each technique suits.
I can explain when distillation is used instead of evaporation.
Before class
A concept tutorial for introducing or revising the techniques. Set the width with ?width=minimum, typical (default) or wider.
The node's response mode is structured reasoning: students confuse distillation with evaporation because both heat a liquid. The Explain sort scaffolds the comparison row by row.
First Nations content: the node file lists steam distilling among First Nations techniques. This tutorial does not claim that. It presents documented traditional tea tree use (crushing and soaking leaves) and makes clear that steam distillation is the modern extraction method. Check with local community knowledge and protocols, and adapt to the Country your school is on.
Running the lesson
Engage: most students predict salty water. Watch the board together to see only water particles cross.
Explore: chromatography is quick to run for real with felt-tip pens, filter paper and water; do it if you can.
Explain: read the sort aloud as a comparison table: same property, different outcome, different equipment.
The hard part (on purpose)
Explaining each technique by the property it uses. When a student says distillation is just evaporation, ask what happens to the steam in each.
When students get stuck
A student says distillation and evaporation are the same. Ask: What happens to the steam in each? Fix: Evaporation lets it escape; distillation cools it and collects it as liquid.
A student says the heavier dyes stay lower. Ask: Which direction does the water carry the dyes? Fix: Up, against gravity. Each dye is carried a different distance because it dissolves and sticks differently.
A student thinks black ink is a single substance. Ask: How many spots came from one black dot? Fix: Several dyes: black ink is a mixture.
Stretch and support
Stretch: Why does salt not travel through the condenser with the water? Use particle motion and boiling points.
Support: Give the comparison as a table with two columns, evaporation and distillation, to fill in before the sort.
Where it leads
Next in class: AC9S7U06 node 5, choosing and justifying a technique for a new mixture, works best as a class task.
Practical: paper chromatography of felt-tip pens or food colourings; a demonstration distillation of coloured water.
What each step is for
Engage: fresh water from seawater: Predicting the collected liquid sets up the key difference from evaporation: the vapour is kept.
Explore: run both techniques: Watching single particles travel through the condenser makes 'collect the vapour' concrete; the chromatogram shows black ink is a mixture.
Explain: distillation is not just evaporation: The node's response mode is structured reasoning: compare the two techniques feature by feature (same property, different outcome, different equipment).
Mix it up: The flat part of a heating curve explains why boiling water holds a steady temperature, which is what the flask in a distillation is doing.
Elaborate: distillation or evaporation?: The choice depends on what you want to keep: if you need the liquid, distil.
Elaborate: three techniques, three properties: Crystallisation, chromatography and distillation each use a different property.
Elaborate: First Nations knowledge and plant oils: Traditional and modern methods of getting substances out of plants both rely on property differences.
Elaborate: reading a chromatogram: Rf values turn a chromatogram into evidence, and a single spot is evidence, not proof.
Now you can
Describe the principle of distillation and of chromatography.
Name a mixture each technique suits.
Explain when distillation is used instead of evaporation.