The Colour Code

Overview

Curriculum Area: Science
Curriculum level: Level 3 of The New Zealand Curriculum
Strand: Material World
Achievement Objective: Students will explore everyday examples of physical and chemical changes. They will begin to link observable phenomena with simple chemical ideas.

Class Level: Year 6
Group size: 4 students
Lesson Duration: 31 minutes

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WALT

We Are Learning To:

• Investigate how substances react differently with a natural acid-base indicator.
• Use our observations to create a colour-coded pH scale.
• Understand and identify common household acids and bases.

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Success Criteria

We will be successful when we:

• Correctly prepare and use red cabbage juice as a pH indicator.
• Identify clear colour changes when different substances are mixed with the indicator.
• Accurately place substances on a simple pH scale using observed colour changes.
• Use scientific language such as ‘acid’, ‘base’, ‘neutral’, and ‘indicator’ when explaining our findings.

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Materials Needed (per group of 4)

• 1/4 head of red cabbage chopped and soaked in hot water to produce indicator (already prepared by teacher and cooled)
• Clear plastic cups or small beakers (1 per test substance)
• Pipettes or droppers
• White tray or sheet (to clearly see colour changes)
• Substances to test:
  • Lemon juice
  • Baking soda solution (1 tsp in 100ml water)
  • Liquid soap or dishwashing liquid (diluted)
  • Vinegar
  • Tap water (as neutral control)
• A3 chart paper and coloured pencils
• Lab coats or aprons (optional but adds a sense of occasion!)
• Safety glasses (optional)
• Printable mini pH colour scale reference (teacher-prepared)

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Lesson Breakdown (31 Minutes)

0:00 – 3:00 | Tuning In (Hook)

• Begin with a brief visual demonstration: Add cabbage indicator to lemon juice in a clear cup—watch it turn bright pink.
• Ask: “What do you think happened here?”
• Briefly recap prior learning: “Remember how we observed baking soda and vinegar bubbling? Today we are going to explore why that happened… using colours.”

Prompt to students: "Can colours help us understand invisible science?"

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3:00 – 6:00 | WALT & Safety Setup

• Clearly state the WALT and Success Criteria.
• Go over science safety: no tasting, wipe spills, handle substances with care.
• Assign each student a role for the investigation:
  • Pourer
  • Recorder (writes down findings)
  • Colour observer
  • Cleaner

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6:00 – 20:00 | Exploration Time – pH Testing

Students will:

1. Add a small amount of cabbage juice to each cup of test substance using droppers.
2. Record the colour change on their Observation Chart (teacher-prepared worksheet with boxes for "Substance", "Colour", "Acid/Base/Neutral").
3. Discuss within their group:
   • What does this colour mean?
   • Is this an acid, base, or neutral?

Walk around, ask guided questions:

• “Why do you think the soap turned greenish-blue?”
• “What’s happening when acid and base mix?”

Encourage scientific vocabulary: "indicator", "reaction", "acidic", "basic", "neutral".

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20:00 – 27:00 | Making Our Own pH Scale

• Students arrange substances from most acidic to most basic based on colour.
• Create a Mini pH Rainbow Poster on A3 chart paper, placing tested substances along a “pH colour strip” made from their observations.
• Label each section with common examples and scientific terms.

Teacher Tip: Keep this for classroom walls to reinforce learning.

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27:00 – 30:00 | Whole-Class Reflection

• Each student shares 1 interesting result with the group.
• Discuss:
  • “Which substance surprised you the most?”
  • “How could we use this in real life?”
• Revisit the WALT and Success Criteria using thumbs:
  👍 = Achieved, 👌 = Working towards, 👎 = Need support

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30:00 – 31:00 | Wrap-Up Call to Action

• Make it real: “At home, could you try this with beetroot or turmeric?”
• Issue a "junior chemist" badge (mini sticker or stamp) for participation and curiosity.

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Extension Activities (for advanced learners)

• pH Prediction Challenge: Give students 2 unknown clear liquids (e.g. orange juice and soda water). Ask them to predict the pH category before testing and justify their reasoning based on taste or fizz.
• Mix & React: Combine an acid and a base from the set (e.g. baking soda + vinegar + cabbage juice) and observe the results—and the colour change. Record not just the colour but also any bubbles or temperature change.
• Cross-Curricular Writing Task: Write a short fictional story titled "The Day I Shrunk and Entered a Cabbage" – explain the pH scale discovery from a cabbage’s point of view!

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Teacher Reflection Prompt (Post-Lesson)

• Did students use scientific vocabulary confidently?
• Did they generate their own pH scale independently or with support?
• How effectively did the group roles support engagement?
• What misconceptions arose that I can address tomorrow?

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Notes for Next Steps

• Reinforce acid/base ideas using classroom drinks next week (e.g. what's happening in fizzy drinks?).
• Link to environmental science: How does pH affect soil or water—could explore in a gardening or freshwater stream unit.

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Let’s keep science vivid, kinaesthetic, and connected to our students' everyday lives — especially with the magic of colour.