All lessons › Change detectives › Lesson 4
Australian primary science · Years 5–6 · Lesson 4 of 6
Get it back
Inquiry question: Sand and salt got mixed into a bucket of water. Can we get both back?
Check practical materials
Problem solving
What students learn
Mixtures can be separated using differences in properties; evaporating the water recovers a dissolved solid, so dissolving is reversible.
Success criteria
- I can explain why filtering traps sand but not dissolved salt.
- I can plan steps in a sensible order.
- I can suggest an improvement to a method and explain why it helps.
Preparation and materials
Before this lesson: Dissolving makes a solution (lesson 3).
- Cups of sandy salt water (1 tsp sand + 1 tsp salt in 100 mL water) — 13
- Funnels — 13
- Filter paper or paper towel — 26 pieces
- Clear cups — 26
- Dark saucers — 13
- Magnifying glasses — 13
- The salt-water saucer from lesson 3 — 1
Teacher setup
- Mix the sandy salt water just before the lesson.
- Check the windowsill saucer; if no crystals yet, leave it another day.
Safety and adaptations
- No tasting. Salt water can sting eyes: wash hands afterwards.
- Wipe spills.
Review your school policies and curriculum requirements before teaching.
How to investigate
The lesson sequence should leave pupils with evidence to interpret, not only an activity to finish.
- Look at last lesson’s saucer with a magnifying glass.
- Plan how to separate the sand and salt. Write the steps in order.
- Filter the mixture. Observe what stays and what goes through.
- Put a few drops of the filtered liquid on a dark saucer to evaporate.
- Evaluate: what didn’t work perfectly? Suggest one improvement.
Teacher modelling prompt
Hold up a cup of cloudy filtered water (made with a torn filter). Model improving a method: “One limitation is that the paper tore. An improvement is to fold the filter carefully and pour slowly, so sand can’t get through.”
Record and explain evidence
Recording question: How can we separate sand and salt from water?
| Step | What we did | What we observed |
|---|---|---|
| ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
Which order works, and why does order matter?
Check understanding
What should pupils know? Why does filter paper trap sand but not salt?
Explain with evidence: Your filtered water was cloudy. Suggest one improvement and explain why it would help.
Apply the idea: How could you separate iron filings from sand?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.