Colour Change Investigation

Overview

Students investigate how red cabbage indicator changes colour when mixed with baking soda, lemon juice, water and vinegar. They use observations and a recording grid to compare substances, identify patterns and communicate evidence-based conclusions about acidic and basic substances.

Learning intentions

• Students will understand that red cabbage juice is a natural indicator.
• Students will observe and record colour changes accurately.
• Students will compare substances and identify evidence of acidic or basic properties.
• Students will plan and carry out a safe, fair scientific investigation.
• Students will communicate findings using observations and scientific vocabulary.

Success criteria

• I can follow a safe method and handle materials responsibly.
• I can record the starting colour, final colour and other observations in a grid.
• I can use evidence to compare lemon juice, vinegar, water and baking soda solution.
• I can explain that colour change gives information about a substance’s properties, but does not identify every substance exactly.

Curriculum links

• Science — Biological Science: designing and carrying out investigations, recording evidence and communicating findings.
• Science — participating in science enquiry by asking questions, making observations, identifying patterns and drawing conclusions.
• Science capabilities: investigating in science, interpreting representations and evidence, and communicating in science.
• Key competencies: thinking; managing self; participating and contributing; relating to others.

Lesson structure (90 minutes)

1. 0–8 min · Hook and question. Teacher opens with the hook and investigation question and shows red cabbage indicator alongside the four test substances. Students predict which samples will change colour and record one reason for their prediction in pairs.

2. 8–20 min · Teach the science and safety. Teacher explains that red cabbage contains a pigment that changes colour in different chemical conditions; introduce the terms indicator, acidic, basic, neutral, observation and evidence. Teacher models goggles, careful pouring, no tasting, handwashing and immediate reporting of spills, then displays the method using the explanation, safety reminders and method slides. Students identify one safety rule and distinguish an observation from a prediction.

3. 20–28 min · Set up the fair test. Teacher places students in five groups of five and provides each group with a tray, four labelled cups or wells, indicator and test substances. Distribute the red cabbage indicator recording grid and agree that the amount of indicator, amount of test substance, container type and observation time will remain the same. Students label their grid, write a prediction and assign roles: equipment manager, measurer, mixer, recorder and safety monitor.

4. 28–55 min · Practical investigation. Teacher circulates, checks safe handling and asks, “What changed, and how do you know?” Groups add equal amounts of red cabbage indicator to each labelled sample, test baking soda solution, lemon juice, water and vinegar, and observe the colour change. Students record the starting colour, final colour, colour description, visible changes and any unexpected result in the results table. They must not taste or directly touch any sample.

5. 55–68 min · Compare and interpret. Teacher pauses the practical, projects the comparison and evidence prompts and supports groups to compare results. Students place their observations alongside another group’s results, identify similarities and differences, and discuss whether their evidence supports their predictions. Groups use cautious language such as “In our test…” and “The colour change suggests…”

6. 68–82 min · Explain and communicate. Teacher models a conclusion using the structure: “The indicator changed from… to… Therefore, the sample showed…” without presenting colour as an exact pH measurement. Students complete the conclusion and evaluation sections of the conclusion and evaluation prompts, including one limitation and one improvement, then prepare a 30-second group report.

7. 82–90 min · Plenary and exit check. Teacher uses the plenary questions to revisit the investigation question. Students share one result and complete an exit response on the worksheet: “Which sample showed the strongest visible change in your test? What evidence supports your answer?” Collect worksheets and supervise careful disposal, bench cleaning and handwashing.

Resources

• the red cabbage indicator investigation slide deck
• the red cabbage indicator recording grid
• Prepared red cabbage indicator solution
• Baking soda mixed with water
• Lemon juice, water and vinegar
• Five group trays with labelled cups or spotting tiles
• Droppers, measuring spoons or small measuring cylinders
• Safety goggles, paper towels, gloves if required by school policy
• Waste container, cleaning cloths and access to water

Assessment

• Check predictions, role allocation and students’ understanding of controlled variables before testing.
• During the investigation, observe safe technique and question students about the difference between an observation and an inference.
• Assess the recording grid and exit response for accurate observations, appropriate comparisons, use of evidence and a sensible limitation or improvement.

Differentiation

• Provide a word bank and sentence starters: “The starting colour was…”, “After mixing…”, “This suggests…”, and “Our evidence is…”. Use a partially completed example on the board.
• Pair students strategically, read instructions aloud and provide enlarged or high-contrast worksheets for students with reading, vision or fine-motor needs. Assign practical roles that allow meaningful participation.
• Support English language learners with photographs or real samples, gestures, repeated vocabulary and opportunities to rehearse explanations with a partner before reporting.
• Extend confident students by asking them to rank the size of the colour changes using a clearly explained scale, compare group reliability, or propose how a pH scale or repeated trials could improve the investigation.