--- marp: true theme: default html: true --- # Quick check: choosing a separation technique Year 7 Chemistry · Pure substances and mixtures --- ## Today **We are learning to** a few quick questions on choosing and justifying a separation technique, and saying why another one would not work. Taught in class; use this to check yourself. - I can match a mixture to a separation technique. - I can put the steps of a separation in a sensible order. - I can say why one technique would not work on a given mixture. --- ## Why it matters > You are handed a mixture you have never seen. How do you decide how to separate it? --- ✅ Check ## Match the technique **Which technique separates this mixture?** Groups: Magnet · Filtering · Evaporation · Distillation · Chromatography Iron filings from sand · Sand from water · Salt from salty water · Pure water from salty water, collecting the water · The colours in a felt-tip ink * Answer: Iron filings from sand → Magnet; Sand from water → Filtering; Salt from salty water → Evaporation; Pure water from salty water, collecting the water → Distillation; The colours in a felt-tip ink → Chromatography --- ✅ Check ## In what order? **A mixture of sand, salt and water is to be separated into all three. Which plan works?** - Filter out the sand, then evaporate the water to leave the salt - Evaporate first, then filter - Use a magnet, then filter - Filter only * Answer: Filter out the sand, then evaporate the water to leave the salt --- ✅ Check ## A technique that fails **Why will filtering not separate salt from salty water?** - The holes are too big to catch any solid - Dissolved salt particles are tiny and pass through the holes in the paper with the water - Filter paper dissolves in water - Salt is too heavy for the paper to hold * Answer: Dissolved salt particles are tiny and pass through the holes in the paper with the water --- ✅ Check ## Exit ticket **Why does a magnet separate iron filings from sand?** * Iron is magnetic and sand is not, so the magnet uses that difference in property.