Colourful Chemistry Fun

---

Lesson Overview

Title: The Science Behind Homemade pH Indicators
Year Level: Year 10
Subject: Science – Chemical Sciences
Class Size: 14 students
Duration: 60 minutes

---

Australian Curriculum Links

Strand: Science Understanding
Sub-strand: Chemical Sciences
Curriculum Reference: ACSSU187 – Different types of chemical reactions are used to produce a range of products and occur at different rates.

Students will apply this outcome by exploring acid–base reactions, understanding neutralisation, and using natural indicators (red cabbage extract) to identify pH changes.

---

Lesson Objectives

By the end of this lesson, students will:

1. Understand the concept of pH and the pH scale.
2. Describe acids, bases, and neutral substances using scientific terminology.
3. Investigate how anthocyanin pigments in red cabbage serve as natural pH indicators.
4. Analyse and interpret colour changes to identify the approximate pH of various substances.
5. Collaborate and communicate findings in a group experimental activity.

---

Materials Required (per group of 2)

• ½ head of red cabbage (pre-chopped)
• Beaker or jug (500mL)
• Blender or hotplate & saucepan (for extracting juice)
• Strainer or cheesecloth
• Transparent plastic cups or test tubes (x6 per group)
• Small spoons or droppers
• Distilled water
• Substances for testing: lemon juice, white vinegar, baking soda, window cleaner, soap water, tap water
• pH paper or digital pH meter (only used after experiment for confirmation)

Safety Equipment:

• Gloves
• Safety goggles
• Lab coats or aprons

---

Lesson Structure

Starter – 'Showstopper Chemistry' (10 minutes)

1. Greet students with a vibrant test tube display of different coloured cabbage juice solutions (rainbow of acids and bases).
2. Ask: "What do you think caused these different colours from the same cabbage extract?"
3. Allow students to brainstorm and discuss briefly in pairs; write predictions on the board.

Engagement tip: Use food analogies like “Our stomach acid is like lemon juice – sharp and sour – can cabbage detect it?”

---

Explicit Teaching – Exploring the Science (10 minutes)

Use whiteboard or digital screen to deliver a fast-paced mini-lecture on:

• What is pH?
  The pH scale ranges from 0–14. Acids (<7), neutral (7), bases (>7).

• What is an indicator?
  Definition: substances that change colour when exposed to acids or bases.

• The chemistry of red cabbage:
  Red cabbage contains anthocyanins, a group of flavonoid pigments that change structure—and therefore colour—depending on the concentration of hydrogen ions (H⁺).

  pH Range	Colour Seen
  1 - 3	Red
  4 - 6	Purple
  7	Blue
  8 - 10	Green
  11 - 14	Yellowish-green

• Include structural diagram of anthocyanins if possible.

---

Hands-On Activity – DIY pH Indicator (30 minutes)

Real-world link: “What if you were stuck on a camping trip without any science equipment and you wanted to test if water was safe to drink?”

Step 1: Extracting the Indicator (Prep Ahead – teacher demo)
Teacher demonstrates on hotplate or blender how to make red cabbage juice.

1. Chop ½ cabbage.
2. Blend with warm water or boil for 10 minutes.
3. Strain out solids – purple juice is the indicator.

Step 2: Group Experiment Setup

Students will work in pairs (7 groups):

• Label 6 cups/test tubes.
• Add ~10mL of cabbage juice to each.
• Add a different test substance to each cup (equal quantities).
• Observe & record the colour change.
• Refer to pH colour chart and estimate pH levels.

Step 3: Data Table Completion

Students create and complete a table like this:

Test Substance	Original Colour	Final Colour	Estimated pH	Acid/Base/Neutral
Lemon Juice	Purple	Red	~2	Acid
…	…	…	…	…

---

Group Discussion & Knowledge Consolidation (5 minutes)

Ask students to reflect:

• Which substances surprised you?
• Did any base turn yellowish?
• Can natural substances be reliable scientific tools?

Encourage students to think about everyday contexts (e.g., soil testing, pool water, health).

---

Plenary – 'Quick Quiz Showdown' (5 minutes)

Divide the class into two groups (7 students each)

Run a fast round of quiz questions:

1. What does the pH scale measure?
2. What natural pigment allows cabbage to change pH?
3. What pH do neutral substances have?
4. What colour does cabbage turn in a strong base?
5. Is vinegar an acid or base?

Award points, mini prizes or win bragging rights!

---

Assessment Opportunities

• Formative assessment:

  • Observation of group discussion and participation
  • Completed data tables and analysis questions
  • Exit quiz performance

• Extension / Homework Task:

  • Create a short presentation or video showing them testing household liquids at home using cabbage juice (teacher discretion)

---

Differentiation Strategies

• For advanced learners:
  Introduce the concept of conjugate acid-base pairs and titration indicators.

• For EAL/D or struggling students:
  Provide colour-coded charts and structured sentence starters: “I think ______ is a base because the solution turned ______.”

---

Teacher Tips & Extensions

• Freeze cabbage extract ahead in ice cube trays – ready to go anytime!
• Use a drop of universal indicator after cabbage test for bonus verification.
• Link this with cross-disciplinary learning:
  Art (colour theory), Food Tech (pickling), Geography (acid rain impact on vegetation).

---

Reflection for Future Planning

• What misconceptions arose?
• Were students engaged with the colour-change element?
• Could this feed into a larger unit on environmental chemistry or laboratory testing?

---

Conclusion

This lesson ignites curiosity about everyday phenomena, reinforces pH foundations, and empowers students to conduct real-world scientific exploration with tools from their kitchen. It’s multimodal, memorable, and directly aligned with Year 10 curriculum outcomes.

Let’s turn cabbage into chemistry—you might even develop your students’ new favourite science memory!