All lessons › Change detectives › Lesson 2
Australian primary science · Years 5–6 · Lesson 2 of 6
Melt it, make it again
Inquiry question: Chocolate melts in your pocket. Is melted chocolate still chocolate?
Check practical materials
Fair testing
What students learn
Melting and freezing are reversible changes of state: no new substance is made.
Success criteria
- I can describe melting and freezing as reversible changes.
- I can look across several results to find a pattern.
- I can spot an unusual result and suggest what to do about it.
Preparation and materials
Before this lesson: The particle model of solids and liquids (lesson 1).
- Foil patty pans — 78 (6 per pair)
- Equal pieces of chocolate, butter and ice — 26 of each (2 per pair)
- Shallow trays of warm tap water (about 40°C, teacher-prepared) — 7 (shared by 2 pairs)
- Timers — 13
- Access to a fridge and a freezer — 1 of each
Teacher setup
- Cut equal-sized pieces of chocolate and butter.
- Fill trays with warm water just before the investigation.
Safety and adaptations
- Check for food allergies. Alternative: ice, coconut oil (keep coconut oil in the fridge until the lesson) and a crayon shaving (which won’t melt at 40°C, a useful contrast).
- The teacher prepares the warm water; no hotter than 50°C.
- No tasting.
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.
- Predict the order in which the three solids will melt.
- Float the three pans in the warm water at the same time. Start the timer.
- Record the time each becomes completely liquid. Repeat if time allows.
- Put the chocolate and butter pans in the fridge and the ice pan in the freezer. Check them later.
- Compare results across the class. What pattern do you see? Any unusual results?
Teacher modelling prompt
Show three ice trials: 2, 3 and 2 minutes. Say: “All three are close, so ice melts in about 2–3 minutes here.” Then show butter: 6, 5 and 11 minutes. Ask: “Which result doesn’t fit? What might have happened?”
Record and explain evidence
Recording question: Which solid melts fastest in warm water, and can each become solid again?
| Sample | Trial 1 (min) | Trial 2 (min) | Solid again after cooling? |
|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
Which claim does your evidence support?
Check understanding
What should pupils know? Is melting chocolate a reversible change? How do you know?
Explain with evidence: One group recorded butter melting in 6, 5 and 11 minutes. What should they do about the 11?
Apply the idea: Candle wax drips and hardens as it cools. Is the dripping wax a reversible change? Explain.
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.