All lessons › Kitchen chemistry: fizz, foam and fountains › Lesson 5
Australian primary science · Years 5–6 · Lesson 5 of 8
Elephant toothpaste
Inquiry question: What makes elephant toothpaste foam so fast?
Check practical materials
Observing
What students learn
A chemical change can be sped up by a substance that isn’t used up. Warmth, a gas and foam are evidence that a new substance has formed.
Success criteria
- I can predict and observe changes during a demonstration.
- I can name several signs that a new substance formed.
- I can explain why this experiment is a teacher demonstration.
Preparation and materials
Before this lesson: Signs of a new substance (lessons 1 and 3).
- 3% hydrogen peroxide (pharmacy) — 1 bottle (250 mL)
- Dried yeast sachet — 1
- Warm water — 3 tablespoons
- Dishwashing liquid — 1 squirt
- Food colouring — a few drops
- Clean 600 mL plastic bottle — 1
- Large tray or tub — 1
- Safety glasses and gloves for the teacher — 1 set
- Cup and spoon to mix yeast — 1
Teacher setup
- Set up on a large tray at the front, at least 2 metres from students.
- Mix the yeast with warm water in a cup and leave for 1 minute.
- Read the peroxide label and keep it out of student reach.
Safety and adaptations
- Teacher demonstration only: students do not touch the hydrogen peroxide, the bottle or the foam.
- Students stay at least 2 metres back.
- The teacher wears safety glasses and gloves.
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 what will happen when the yeast is added. Give a reason.
- Watch your teacher add soap and food colouring to the hydrogen peroxide. Record what you see.
- Watch the yeast go in. Record what happens to the foam and how fast.
- Listen: your teacher will tell you whether the bottle feels warm. Record it.
- List every sign that a new substance formed.
- Why is this a teacher-only experiment?
Teacher modelling prompt
Teacher demonstration: put the bottle on the tray. Add 1/2 cup hydrogen peroxide, a squirt of dish soap and food colouring. Ask students to predict. Pour in the yeast mixture and step back. After the foam slows, touch the bottle (gloved) and report whether it feels warm. Ask: “What evidence tells us something new formed?”
Record and explain evidence
Recording question: What evidence shows that a new substance formed?
| What happened | What I observed | Sign of a new substance? |
|---|---|---|
| ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
What evidence suggests a reaction, not just soap bubbles?
Check understanding
What should pupils know? What gas filled the foam?
Explain with evidence: Which two observations together are the best evidence of a chemical change?
Apply the idea: Why do schools keep chemicals like hydrogen peroxide for teachers only?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.