How do you separate a mixture?

Classroom resources

Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.

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Students will be able to

• 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.

Timing

Engage and Explore 10 min · Explain 8 min · Evaluate 3 min · Typical adds 4 min, Wider about 12 min

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

1. Engage: ask what 'heavier' would predict for an aluminium can full of sand. Weight is the common default explanation.
2. Explore: let students make the wrong order first. Ask what is in the filter paper and why.
3. 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

Answers to the checks

1. Engage: the recycling magnet: A magnet lifts steel cans but leaves aluminium cans behind. Why?
   Magnetism: steel is attracted to magnets and aluminium isn't. Every separation uses a difference in a property like this.
2. Explore: the separation bench: Get iron, sand and salt each on its own.
   
3. Property to technique: Which technique uses each property difference?
   Iron is magnetic; sand isn't. → Magnet; Sand grains are too big to pass through filter paper; water and dissolved salt pass through. → Filtration; Water boils at 100 °C; salt doesn't boil until 1413 °C. → Evaporation; Pebbles are much bigger than grains of rice. → Sieving; Oil is less dense than water, so it floats on top. → Letting it settle, then pouring off
   Each technique uses one property difference.
4. Filter paper: Why does filter paper catch the sand but not the salt?
   Sand grains are too big for the tiny holes; dissolved salt is spread out as single particles small enough to pass through
   Filter paper sorts by particle size.
5. The order: Why did the magnet have to come before the filter paper?
   Iron and sand are both too big for the filter, so filtering first would trap them together
   The magnet picks out just the iron first; then the filter only catches sand.
6. What they share: What do all separation techniques have in common?
   Each one uses a difference in a physical property between the parts of the mixture
   Find a property where the parts differ, then choose the technique that uses it.
7. Mix it up: Looking back at density: air is much less dense than water. Why?
   Air particles are far apart, so there are far fewer in each cm³
   Fewer particles in each cm³ means less mass in each cm³: lower density. Density is one of the property differences a separation can use.
8. Elaborate: choose, and rule out: You need to get chalk dust back out of chalky water. Chalk doesn't dissolve. Judge each technique.
   Filtration → Best choice; Evaporation → Works, but not the best; A magnet → Won't work; A kitchen sieve → Won't work
   Name the property difference, then rule out techniques that can't use it.
9. 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. → Density; Making fresh water from seawater by boiling it and cooling the steam. → Boiling point; Sifting flour to remove lumps. → Particle size; Leaving fresh milk to stand so the cream rises to the top. → Density
10. Elaborate: home, recycling and clean water: Which property difference does each one use?
    Home: a tea bag keeps the leaves out of your cup. → Particle size; Recycling: overhead magnets pull steel cans off the conveyor belt. → Magnetism; Recycling: air jets blow light paper and plastic film off heavier glass and metal. → Density; Water treatment: water sits in big tanks so mud sinks to the bottom. → Density; Water treatment: water trickles through deep beds of sand. → Particle size
11. 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.
    see the program below
    Filtering removes the mud (particle size) and boiling kills germs, so combining them is best. Boiling alone makes it safer but leaves mud. A cloth alone removes some mud but not germs.

    Filter through a clean cloth, then boil
    Boil only
    Filter through a cloth only
    Drink it straight from the creek
    

12. The jug filter: An alert says: "Boil water, then let it cool, before drinking. A jug filter is not enough." Why include the jug filter line?
    Many homes own jug filters and might trust them, but most aren't designed to remove germs
    Good science communication answers the question its audience will actually have, and heads off the mistake they are likely to make.
13. Reaching everyone: Does each choice help the alert reach and protect everyone?
    Short, plain instructions: boil, cool, then drink → Helps; Naming the suburbs affected and when it started → Helps; Versions in the main languages spoken in the town → Helps; Only a long table of lab results, with no instructions → Gets in the way; Posting it only in a technical report on the water company's website → Gets in the way

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.

Coach prompt (optional)

For a student who has done the lesson and is still stuck. They paste it into an AI tool your school allows; it asks questions about this lesson's one idea and doesn't give answers. Students see it on the course recap page only through a link ending in ?coach=1: recap with coach prompts.

You are a patient science coach for a Year 7 student in Australia. Help me understand ONE idea only, from the lesson "How do you separate a mixture?".

The idea: Properties as the basis for separation: I can explain that separation techniques exploit differences in physical properties and match property differences to techniques.

What understanding looks like:
- States that separation exploits differences in physical properties
- Correctly matches at least 3 property differences to separation techniques
- Explains why a chosen technique would work for a given mixture

Mistakes students often make here:
- A student says the filter catches sand because it is heavier.
- A student says the salt disappeared when it dissolved.
- A student lists techniques without properties.

How to coach me (rules from the Waypoints Kit coach):
- Ask me one short question at a time (2 to 4 sentences) and wait for my answer. Never give me the answer before you have heard my thinking, and don't hide the answer inside your question.
- Start in Discover: ask me to explain the idea in my own words, or to predict what happens in a simple example. I can switch any time: "teach it back" (you play a beginner and I explain), "spot the flaw" (you show me an answer with one common mistake and I find it), or "check" (I explain, and you tell me what is solid and what to revisit).
- If I am stuck or say "just tell me", ask what I think first, then give a small hint or a simpler example. Explain only after I have had a real go.
- If I seem to be missing the idea that comes before this one (Pure substances vs mixtures at the particle level), check it quickly, then come back.
- Stay in this idea: don't teach later ideas or add extra content. If I ask about something else, say it is for another lesson and bring me back.
- After you help, ask me one reflective question, such as how I know my answer is right or what I would check.
- Praise my effort and method, not my ability.
- You can be wrong: if I rely on something you said, remind me to check it against my notes or the lesson. If you don't know, say so.
- Use simple words.
- Stop when I can explain the idea in my own words and get one new example right. Then tell me to go back to the lesson "How do you separate a mixture?".

Exit ticket

Why does a magnet separate iron filings from sand?

Iron is magnetic and sand isn't: the magnet uses that difference in property.

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.

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.