---
title: "Quick check: choosing a separation technique"
subtitle: "Year 7 Chemistry · Pure substances and mixtures · Lesson 10"
---

# Quick check: choosing a separation technique

**Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}}

> **Key question:** You are handed a mixture you have never seen. How do you decide how to separate it?


:::teacher-note

**In one sentence:** A self-test on choosing and justifying a separation technique for a mixture, and saying why another would fail (AC9S7U06, node 5, a hinge node taught in class).

**Students should be able to say:** 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.

**Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet.

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## Choose and justify


:::keep-together

### Match the technique

**Which technique separates this mixture?**

Groups: Magnet, Filtering, Evaporation, Distillation, Chromatography

- Iron filings from sand: {{field-15}}
- Sand from water: {{field-15}}
- Salt from salty water: {{field-15}}
- Pure water from salty water, collecting the water: {{field-15}}
- The colours in a felt-tip ink: {{field-15}}

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:::teacher-note

**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

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:::keep-together

### 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

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:::teacher-note

**Answer:** Filter out the sand, then evaporate the water to leave the salt

Filtering removes the sand because it is too big to pass through. The salt is dissolved, so it passes through with the water; evaporating the water leaves the salt.

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:::keep-together

### 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

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:::teacher-note

**Answer:** Dissolved salt particles are tiny and pass through the holes in the paper with the water

Filtering separates by particle size. Dissolved particles are far smaller than the holes, so they go through.

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## Exit ticket

:::keep-together

**Why does a magnet separate iron filings from sand?**

{{lines-3}}

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:::teacher-note

**Answer:** Iron is magnetic and sand is not, so the magnet uses that difference in property.

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