--- marp: true theme: default html: true --- # How do you separate a mixture? Year 7 Chemistry · Pure substances and mixtures --- ## Today **We are learning to** 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. - 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. --- ## Why it matters > 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. --- 💬 Discussion ## Engage: predict **A magnet lifts steel cans but leaves aluminium cans behind. Why?** - Steel is attracted to magnets and aluminium isn't - Steel cans are bigger - Aluminium cans are too light to be picked up - The magnet only lifts heavier things --- ✍️ Activity ## Explore it {{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry%2Fseparating%2Fstep-2&code=widget%3A+bench%0A}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry/separating/?full=step-2#step-2) --- ✅ Check ## What happened? * Magnetism: steel is attracted to magnets and aluminium isn't. Every separation uses a difference in a property like this. --- ✅ Check ## Property to technique **Which technique uses each property difference?** Groups: Magnet · Filtration · Evaporation · Sieving · Letting it settle, then pouring off Iron is magnetic; sand isn't. · Sand grains are too big to pass through filter paper; water and dissolved salt pass through. · Water boils at 100 °C; salt doesn't boil until 1413 °C. · Pebbles are much bigger than grains of rice. · Oil is less dense than water, so it floats on top. * Answer: 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 --- ✅ Check ## Filter paper **Why does filter paper catch the sand but not the salt?** - Salt is lighter than sand - The salt has disappeared - Sand grains are too big for the tiny holes; dissolved salt is spread out as single particles small enough to pass through - Sand sticks to the paper * Answer: Sand grains are too big for the tiny holes; dissolved salt is spread out as single particles small enough to pass through --- ✅ Check ## The order **Why did the magnet have to come before the filter paper?** - It's the rule for separating - Magnets don't work underwater - Iron and sand are both too big for the filter, so filtering first would trap them together * Answer: Iron and sand are both too big for the filter, so filtering first would trap them together --- ✅ Check ## What they share **What do all separation techniques have in common?** - Each one turns the mixture into new substances - Each one separates the heavier part from the lighter part - Each one needs heat - Each one uses a difference in a physical property between the parts of the mixture * Answer: Each one uses a difference in a physical property between the parts of the mixture --- ✅ Check ## Mix it up **Looking back at density: air is much less dense than water. Why?** - Air has no mass - Each air particle is lighter than a water particle - Air particles are smaller - Air particles are far apart, so there are far fewer in each cm³ * Answer: Air particles are far apart, so there are far fewer in each cm³ --- ✅ Check ## Elaborate: choose, and rule out **You need to get chalk dust back out of chalky water. Chalk doesn't dissolve. Judge each technique.** Groups: Best choice · Works, but not the best · Won't work Filtration · Evaporation · A magnet · A kitchen sieve * Answer: Filtration → Best choice; Evaporation → Works, but not the best; A magnet → Won't work; A kitchen sieve → Won't work --- ✅ Check ## Elaborate: size, density and boiling point **Which property difference does each one use?** Groups: Particle size · Density · Boiling point · Magnetism Panning for gold: swirling water washes away gravel and leaves gold flakes in the pan. · Making fresh water from seawater by boiling it and cooling the steam. · Sifting flour to remove lumps. · Leaving fresh milk to stand so the cream rises to the top. * Answer: 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 --- ✅ Check ## Elaborate: home, recycling and clean water **Which property difference does each one use?** Groups: Particle size · Density · Boiling point · Magnetism Home: a tea bag keeps the leaves out of your cup. · Recycling: overhead magnets pull steel cans off the conveyor belt. · Recycling: air jets blow light paper and plastic film off heavier glass and metal. · Water treatment: water sits in big tanks so mud sinks to the bottom. · Water treatment: water trickles through deep beds of sand. * Answer: 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 --- ✅ Check ## 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.** ```science Drink it straight from the creek Boil only Filter through a cloth only Filter through a clean cloth, then boil ``` --- ✅ Check ## 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?** - Jug filters make the water less safe - Filtering removes germs better than boiling, so the alert has it wrong - Many homes own jug filters and might trust them, but most aren't designed to remove germs * Answer: Many homes own jug filters and might trust them, but most aren't designed to remove germs --- ✅ Check ## Reaching everyone **Does each choice help the alert reach and protect everyone?** Groups: Helps · Gets in the way 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 instructions · Posting it only in a technical report on the water company's website * Answer: 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 --- ## 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. --- ✅ Check ## 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.