Every separation technique uses a difference in a physical property between the parts of a mixture. Match property differences to techniques, and choose the order.
A recycling plant lifts steel cans out of the rubbish with a giant magnet and leaves everything else behind. Every way of separating a mixture works like that: it uses a difference between the parts.
Separating doesn't change the particles: you get back the same substances you mixed. The trick is to find a property where the parts differ.
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: the recycling magnet
ExploreTry it on the board and compare what happens with your prediction.
Explore: the separation bench
The beaker holds water with dissolved salt, sand and iron filings. Use the tools to get iron, sand and salt each on its own. The order matters, and you can start again.
Try it yourselfNothing is saved: start again as often as you like.
Get iron, sand and salt each on its own.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: why each technique works
In your book: explain how you separated the iron, sand and salt. For each step, name the property difference you used.
Which technique uses each property difference?
Iron is magnetic; sand isn't.Magnetism.
Sand grains are too big to pass through filter paper; water and dissolved salt pass through.Particle size.
Water boils at 100 °C; salt doesn't boil until 1413 °C.Boiling point.
Pebbles are much bigger than grains of rice.Particle size, with bigger holes.
Oil is less dense than water, so it floats on top.Density.
PractiseA few on your own, to check you have it.
Mix it up
Elaborate TypicalUse the same idea in a new context.
Elaborate: choose, and rule out
You need to get chalk dust back out of chalky water. Chalk doesn't dissolve. Judge each technique.
FiltrationChalk particles don't dissolve and are too big for the filter paper.
EvaporationIt leaves the chalk, but takes a lot of energy and also leaves any dissolved minerals mixed in.
A magnetChalk isn't magnetic.
A kitchen sieveChalk dust is far smaller than the holes.
Elaborate WiderUse the same idea in a new context.
Elaborate: size, density and boiling point
Which property difference does each one use?
Panning for gold: swirling water washes away gravel and leaves gold flakes in the pan.Gold is very dense, so it stays at the bottom.
Making fresh water from seawater by boiling it and cooling the steam.Water boils far below salt, so only water turns to steam.
Sifting flour to remove lumps.Lumps are too big for the mesh.
Leaving fresh milk to stand so the cream rises to the top.Cream is less dense than the rest of the milk.
Elaborate WiderUse the same idea in a new context.
Elaborate: home, recycling and clean water
Which property difference does each one use?
Home: a tea bag keeps the leaves out of your cup.The leaves are too big for the bag's tiny holes.
Recycling: overhead magnets pull steel cans off the conveyor belt.Steel is magnetic.
Recycling: air jets blow light paper and plastic film off heavier glass and metal.Light, thin materials are carried by the air.
Water treatment: water sits in big tanks so mud sinks to the bottom.Mud particles are denser than water.
Water treatment: water trickles through deep beds of sand.Small particles get trapped between the sand grains.
Elaborate WiderUse the same idea in a new context.
Elaborate: muddy creek water
On a camping trip, the only water is from a muddy creek, and it may contain germs. Order these plans from most effective to least effective at making it safe to drink.
Pieces (click to add)
Your program
Elaborate TypicalUse the same idea in a new context.
Elaborate: a boil water alert
After a flood, or a fault at a treatment plant, tests sometimes find germs in a town's water. The health department and the water company then issue a boil water alert. The tests are science; the alert is science communication. It turns the results into something every household can act on, and it is lifted only when new tests show the water is safe again.
Does each choice help the alert reach and protect everyone?
Short, plain instructions: boil, cool, then drink
Naming the suburbs affected and when it started
Versions in the main languages spoken in the town
Only a long table of lab results, with no instructionsThe results matter to the health department, but households need to know what to do.
Posting it only in a technical report on the water company's websitePeople need it where they already look: text messages, radio, social media, the local news.
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Why did you think the magnet worked? Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Every separation technique uses a difference in a physical property between the parts of a mixture.
Magnetism → magnet. Particle size → sieving or filtration. Boiling point → evaporation. Density → letting it settle and pouring off.
Separating doesn't change the particles: you get back the same substances you mixed.
Order matters: use the technique that picks out one part before one that traps several together.
For teachers
Students explain that separation techniques use differences in physical properties, and match property differences to techniques (AC9S7U06, node 2, a hinge node). About 25 minutes.
I can say that separation techniques use differences in physical properties.
I can match at least three property differences to a separation technique.
I can explain why a chosen technique works for a given mixture.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider.
Hinge: students who can't map property differences to techniques apply techniques by rote. On the bench, filtering before using the magnet traps iron and sand together; that is deliberate, and students can fix it with the magnet.
The creek task is about effectiveness: boiling makes water safer from germs but does not remove chemical pollution.
Running the lesson
Engage: ask what 'heavier' would predict for an aluminium can full of sand. Weight is the common default explanation.
Explore: let students make the wrong order first. Ask what is in the filter paper and why.
Explain: insist the written explanation names a property for every step.
The hard part (on purpose)
Naming the property each technique uses. When a student lists a technique, ask what is different about the two parts that it relies on.
When students get stuck
A student says the filter catches sand because it is heavier. Ask: What does the filter paper actually test, weight or size? Fix: Size: sand grains don't fit through the holes; dissolved salt particles do.
A student says the salt disappeared when it dissolved. Ask: What was left after evaporating? Fix: The salt was there all along, spread out as single particles.
A student lists techniques without properties. Ask: What is different about the two parts that this technique uses? Fix: Every technique pairs with one property: size, density, boiling point or magnetism.
Stretch and support
Stretch: Design a way to separate a mixture of salt, sand, iron filings and wood shavings. What is the best order, and why?
Support: Give a two-column table, property and technique, to fill in as they use the bench.
Where it leads
Next: filtration and evaporation in detail (node 3), then distillation and chromatography (node 4).
In class: a separation practical with sand, salt and iron filings, planned using this property table.
What each step is for
Engage: the recycling magnet: Students often explain separation by weight or size by default; magnetism is a clean property that exposes this.
Explore: the separation bench: Choosing tools on a real mixture, where order matters, turns property-technique pairs into reasoning instead of a list.
Explain: why each technique works: Naming the property behind each technique, and why the order mattered, is the node's checkpoint.
Mix it up: Density is one of the property differences that separation uses, and the particle explanation of density comes from the squashing lesson.
Elaborate: choose, and rule out: Justifying a choice includes saying why the other techniques would not work.
Elaborate: size, density and boiling point: The same few properties sit behind techniques students already know from home.
Elaborate: home, recycling and clean water: Recognising the property in industrial and environmental contexts shows the principle transfers.
Elaborate: muddy creek water: Real choices weigh effectiveness and practicality, and often combine techniques.
Elaborate: a boil water alert: A boil water alert turns test results into one clear action for a whole town: science communication shaping what people do.
Now you can
Say that separation techniques use differences in physical properties.
Match at least three property differences to a separation technique.
Explain why a chosen technique works for a given mixture.