All lessons › Kitchen chemistry: fizz, foam and fountains › Lesson 2
Australian primary science · Years 5–6 · Lesson 2 of 8
Acid or base? Strip test
Inquiry question: Which kitchen liquids are acids and which are bases?
Check practical materials
Classifying
What students learn
Acids and bases are groups of substances with opposite properties. An indicator changes colour to show whether a liquid is acidic, neutral or basic.
Success criteria
- I can use an indicator strip and a colour chart.
- I can sort liquids into acids, neutral and bases.
- I can explain my groups using my test results.
Preparation and materials
Before this lesson: Students know materials have properties we can observe.
- pH test strips with colour chart (or red cabbage indicator) — 1 pack of 100
- Lemon juice — 1 small bottle
- White vinegar — 1 bottle
- Bicarb soda dissolved in water — 1 jug
- Milk — 1 small carton
- Tap water — 1 jug
- Dishwashing liquid mixed with water — 1 jug
- Small cups, labelled — 78 (6 per pair)
- Safety glasses — 26
- Paper towel — 1 roll
Teacher setup
- Pour about 2 cm of each liquid into labelled cups for each pair.
- Optional: make red cabbage indicator by soaking chopped cabbage in warm water, then strain.
Safety and adaptations
- Wear safety glasses: vinegar and lemon juice sting eyes.
- Don’t taste anything in a science lesson.
- Never test cleaning products like bleach or drain cleaner.
- Wash hands afterwards.
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 on safety glasses.
- Dip a new strip into the first liquid for one second.
- Match the colour to the chart straight away. Record the number.
- Use a new strip for each liquid.
- Sort the liquids into acids, neutral and bases.
- Which liquid was the strongest acid? The strongest base?
Teacher modelling prompt
Dip a strip into tap water for one second, then hold it beside the chart. Say: “Look straight away and match the closest colour. That’s our reference. Now you test the rest.”
Record and explain evidence
Recording question: Which kitchen liquids are acids and which are bases?
| Liquid | Strip colour | pH number | Acid, neutral or base? |
|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
Which results support Claim B best?
Check understanding
What should pupils know? What does an indicator do?
Explain with evidence: A strip in orange juice turned the same colour as vinegar. What can you conclude?
Apply the idea: Why do we use strips instead of tasting to test liquids?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.