Colourful Cabbage Chemistry

Overview

This 30-minute lesson is the third in the "Curious Chemistry Adventures" unit for Year 6. Students will engage in an investigative practical activity using red cabbage juice as a natural indicator to test the pH of common household liquids. This lesson directly supports the Chemistry strand of the National Curriculum for England, promoting scientific enquiry skills alongside key chemical concepts involving acids, bases, and pH.

National Curriculum Links

Key Stage 2 Science: Chemistry

Pupils should be taught to:
- Compare and group materials together according to whether they are solids, liquids or gases
- Observe that some materials change state when they are heated or cooled, and measure or research the temperature at which this happens
- Use knowledge of solids, liquids, and gases to decide how mixtures might be separated, including through filtering, sieving and evaporating
- Recognise that some changes result in the formation of new materials, and that this kind of change is not usually reversible, including changes associated with burning and the action of acid on bicarbonate of soda.

Key Scientific Enquiry Skills:

Planning different types of scientific enquiries to answer questions, including recognising and controlling variables where necessary
Taking measurements, using a range of scientific equipment, with increasing accuracy and precision
Recording data and results of increasing complexity using scientific diagrams and labels, classification keys, tables, scatter graphs, bar and line graphs
Using test results to make predictions to set up further comparative and fair tests
Reporting and presenting findings from enquiries, including conclusions, causal relationships and explanations of and degree of trust in results, in oral and written forms such as displays and other presentations.

Learning Objectives

By the end of the lesson, the pupil will be able to:

Explain the scientific concept of pH as a measure of acidity and alkalinity.
Prepare and use red cabbage juice as a natural pH indicator.
Test a variety of household liquids (e.g., lemon juice, washing-up liquid, milk) and classify them as acidic, neutral, or basic using cabbage juice.
Record observations clearly and relate colour changes to the pH scale.
Discuss the importance of pH in real-life contexts such as gardening and cooking.

Resources Needed

Fresh red cabbage leaves (or pre-prepared cabbage juice)
Hot water and containers to extract cabbage juice
Clear plastic cups or small transparent containers (6-8 per session)
Household liquids for testing (e.g., lemon juice, vinegar, milk, washing-up liquid, water)
White paper or laminated sheets for recording observations
pH scale colour chart (prepared using cabbage juice or printed)
Safety goggles and aprons (for the experimental activity)
Worksheets for results recording and reflection
Paper towels for spillages

Lesson Outline

1. Starter Activity (5 minutes)

Begin with an engaging question: “How do you know if something is an acid or base without tasting it?”
Show examples of familiar acidic and basic substances in the kitchen (lemon, soap).
Introduce red cabbage juice as a natural indicator that changes colour depending on pH.
Briefly recap previous lessons covering the unit to consolidate prior learning (material states and chemical changes).

2. Main Activity: Investigative Practical (20 minutes)

Step 1: Prepare the Indicator (if not pre-prepared)

Demonstrate chopping cabbage and soaking in hot water to create purple cabbage juice.
Highlight safety and cleanliness.

Step 2: Testing Liquids

Jude tests 6-8 household liquids by adding equal amounts of cabbage juice to each clear cup.
Observe and record the resulting colour changes (pink/red = acid; purple = neutral; green/yellow = alkali).
Use the pH colour chart to estimate approximate pH values.
Encourage use of scientific vocabulary: acidic, alkaline (basic), neutral.

Step 3: Recording and Discussion

Jude notes results on the worksheet, classifying each liquid accordingly.
Discussion prompt: “Why might it be useful to know the pH of substances around us?”
Explain how gardeners test soil acidity to grow healthy plants; chefs adjust acidity in cooking.

3. Plenary and Assessment (5 minutes)

Ask Jude to summarise what the test showed about acids and bases, referring to the colour changes.
Quick quiz: Match household liquids to their pH category (acid, neutral, alkali).
Reflect on how natural indicators can be an alternative to electronic pH meters.
Teacher assesses understanding through observation of ability to classify acids/bases accurately and explain the significance of pH.

Differentiation

Provide labelled pH colour charts and simplified worksheets for students needing extra support.
Challenge more able learners to predict pH of untested liquids before testing, or research other natural indicators.
For students working with intense sensory sensitivities, provide gloves and ensure gentle aromas only.

Health & Safety

Use appropriate PPE: goggles, aprons.
Ensure liquids tested are safe and non-toxic.
Handle hot water carefully during indicator preparation.
Clean spills immediately.

Extension Ideas

Investigate how different soil samples affect plant health by testing soil pH with cabbage juice.
Explore the chemistry behind the colour changes – anthocyanin pigments in cabbage reacting with H+ or OH- ions.
Use digital microscopes or apps to record and zoom in on liquid samples and cabbage cell structure.

Teacher Notes

Red cabbage juice is a cost-effective, visually exciting, and age-appropriate way to introduce chemical indicators to Year 6 pupils.
This lesson blends practical inquiry with real-world relevance, supporting greater scientific literacy around everyday chemistry.
Encouraging curiosity and accurate observation will build core enquiry skills essential for Key Stage 3 science readiness.

End of lesson plan.