All lessons › Kitchen chemistry: fizz, foam and fountains › Lesson 4
Australian primary science · Years 5–6 · Lesson 4 of 8
Sherbet and lemonade
Inquiry question: What makes sherbet fizz on your tongue?
Check practical materials
Testing an idea
What students learn
Sherbet contains a dry acid and a dry base. They only react when water is added, making carbon dioxide gas. The amounts of each change how much it fizzes.
Success criteria
- I can explain why sherbet only fizzes when it gets wet.
- I can change the amount of one ingredient and compare the fizz.
- I can use the pH of lemonade to explain why it tastes sour.
Preparation and materials
Before this lesson: Acid and base reactions (lesson 3).
- Citric acid (supermarket baking aisle) — 1 small packet
- Bicarbonate of soda — 1 box
- Icing sugar — 1 small bag
- Lemons or bottled lemon juice — 6 lemons or 1 bottle
- Sugar — 1 small bag
- Water — 1 jug per table
- Clear cups — 52 (4 per pair)
- Teaspoons and stirrers — 26
- pH test strips — 1 pack
- Small paper bags or cups for tasting — 26
- Safety glasses — 26
Teacher setup
- Food lesson: use a clean food-only area and new, food-only equipment. Check allergies and your school’s food policy first. Only taste if your teacher says so.
- Keep tasting ingredients and cups separate from science equipment.
Safety and adaptations
- Food lesson: use a clean food-only area and new, food-only equipment. Check allergies and your school’s food policy first. Only taste if your teacher says so.
- Citric acid stings eyes and cuts: wear safety glasses while mixing the powders, and don’t touch your face.
- Only taste the sherbet you made in a clean tasting cup, a tiny amount, if your teacher allows it.
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.
- Mix recipe A: 1 spoon citric acid, 1 spoon bicarb, 2 spoons icing sugar.
- Mix recipe B: 1 spoon citric acid, 1/2 spoon bicarb, 2 spoons icing sugar.
- Put 1 level teaspoon of each into a cup of water. Time how long it fizzes and describe the fizz.
- Make lemonade: juice of half a lemon, 1 spoon sugar and 1 cup water. Test its pH.
- Which sherbet fizzed best? Why does lemonade taste sour?
- Tasting: only if your teacher says so, a tiny amount from a clean cup.
Teacher modelling prompt
Drop one level teaspoon of icing sugar into a cup of water and start a timer. Nothing fizzes. Say: “That’s how to test each sherbet: same spoon, same water, start the timer. Now find out which recipe fizzes best.”
Record and explain evidence
Recording question: Which sherbet recipe fizzes best, and why?
| Recipe | Fizz time (seconds) | What the fizz looked like | pH (lemonade) |
|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
Which test result shows Claim A is wrong?
Check understanding
What should pupils know? Why does sherbet only fizz when it gets wet?
Explain with evidence: Recipe B had less bicarb and fizzed for less time. Why?
Apply the idea: Bath bombs fizz in water. What two kinds of ingredients might be in them?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.