All lessons › Change detectives › Lesson 5
Australian primary science · Years 5–6 · Lesson 5 of 6
Something new
Inquiry question: Why can’t toast be turned back into bread?
Check practical materials
Observing over time
What students learn
Irreversible changes make new substances; evidence includes a gas produced, colour change, a temperature change (getting hotter or colder), light, and difficulty undoing the change.
Success criteria
- I can name signs that a new substance may have formed.
- I can explain why one sign alone isn’t proof.
- I can classify a change as reversible or irreversible using several pieces of evidence.
Preparation and materials
Before this lesson: Reversible changes: melting and dissolving (lessons 2–4).
- Bicarbonate of soda — 1 box
- White vinegar — 1 bottle
- Zip-lock bags or small cups — 13
- Teaspoons — 13
- Safety glasses — 26
- Jars for rust test — 3 (class set)
- Plain steel wool pieces (no soap) — 3
- Gloves for handling steel wool — 1 pair
- Slice of bread and slice of toast in sealed bags — 1 of each per group
Teacher setup
- Cut steel wool pieces in advance (wear gloves).
- Label rust jars: dry, water, salty water.
Safety and adaptations
- Safety glasses for the bicarb and vinegar reaction; vinegar stings eyes.
- Gloves for steel wool; it can splinter.
- Don’t seal containers of bicarb and vinegar tightly.
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.
- Put about 50 mL of vinegar in a cup (or an open bag). Add 1 spoon of bicarb. Do not seal it. Record everything you notice.
- Rust jars: set up steel wool in dry, water and salty water jars. Record how each looks now.
- Bread and toast: compare the two slices through the bags. List differences.
- For each change, list the evidence for a new substance. Which evidence is strongest?
Teacher modelling prompt
Ask: “Boiling water bubbles, and so does bicarb in vinegar. Is bubbling always evidence of a new substance?” Explain that boiling water’s bubbles are water vapour, which condenses back into water. Model weighing evidence: several signs plus “can it be undone?”
Record and explain evidence
Recording question: What evidence shows that a new substance has formed?
| Change | What I observed | Evidence of a new substance? | Can it be undone? |
|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
Which claim is better supported, and what evidence would you use?
Check understanding
What should pupils know? Give two signs that a new substance may have formed.
Explain with evidence: Bubbles appear when water boils. Is that evidence of a new substance? Explain.
Apply the idea: When you fry an egg, the clear part turns white and solid. Reversible or irreversible? What is your evidence?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.