Understanding pH and Indicators

National Curriculum Links

Science Key Stage 3 – Chemistry

• Describe the properties of acids and bases (pH scale) and how indicators are used to classify substances as acidic, neutral or alkaline.
• Use appropriate scientific vocabulary and symbols, including pH, acid, alkali, indicator.
• Plan and carry out enquiries, including accurate measurements, presentation of data and use of scientific equipment.

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Lesson Details

Year Group: 7
Class Size: 30 students (44.4% SEND)
Duration: 50 minutes
Unit: Chemical Changes Uncovered (Lesson 2 of 5)
Lesson Title: Understanding pH and Indicators

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Learning Objectives (WALT)

• WALT: Understand what pH is and how indicators work to identify acids and alkalis.

Success Criteria

• I can explain what the pH scale measures.
• I can identify the colours of litmus and universal indicators.
• I can classify substances as acidic, neutral, or alkaline based on pH.

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Key Vocabulary

• pH scale
• Acid
• Alkali (Base)
• Neutral
• Indicator
• Litmus
• Universal indicator

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Resources

• Colour-coded pH charts (large print and dyslexia-friendly fonts)
• Litmus paper (red and blue)
• Universal indicator solution and paper
• Selection of household substances (lemon juice, baking soda solution, water, vinegar) in safe, labelled containers
• Whiteboards and pens for student answers
• Worksheets with dyslexia-friendly font and clear formatting
• Materials for extension activity (A3 paper, markers, glue, cut-outs of household items)

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Lesson Structure

1. Do It Now – Retrieval Practice (7 minutes)

• Quick recall quiz on last lesson’s key points (Chemical vs Physical changes).
• Include 2 questions linking last lesson and today’s topic: “What do you think happens to metals in acids?” and “Have you heard of pH before? What does it measure?”
• Use whiteboards for students to write answers; teacher collects and gives instant feedback.
• Purpose: Activate prior knowledge and set context.

2. Introduction to pH (10 minutes)

• Teacher-led interactive discussion on what pH means: measure of how acidic or alkaline a substance is.
• Present a large, colour-coded pH scale (0-14) prominently, explaining the scale visually and numerically.
• Define acids (pH < 7), neutral (pH=7), and alkalis (pH > 7) with examples.
• Use visuals and clear dyslexia-friendly print materials.
• Recap key terms to support language acquisition.

3. Exploration of Indicators and Demonstration (10 minutes)

• Explain what indicators are and how litmus paper and universal indicator work—changing colour to show pH.
• Demonstrate using litmus paper and universal indicator on three household solutions (acidic lemon juice, neutral water, alkaline baking soda solution).
• Students observe and note colour changes on their own pH charts.
• Use colour-coded pH charts for visual support; allow SEND students to work in pairs and ask scaffolded questions.

4. Group Activity: Investigate and Classify (15 minutes)

• Students in small groups test assigned household substances with indicators.
• Record observations on worksheet: colour changes and estimated pH using charts.
• Groups classify each substance as acid, neutral, or alkali.
• Sendensory-friendly workspace and simple language prompts available for SEND students.
• Teacher circulates, checking understanding and supporting groups.

5. Plenary and Success Criteria Check (5 minutes)

• Whole-class discussion answering:
  • What did you learn about pH today?
  • How do indicators help us?
• Students self-assess using success criteria checklist (can be coloured for dyslexic accessibility).
• Teacher clarifies misconceptions.

6. Extension Activity (Home Learning or Enrichment)

• Students create a pH scale poster labelled with the colours and household substances tested in class (or others they research).
• Encourage use of drawings, colours, and sentences explaining acidity/alkalinity.
• Suitable for advanced learners to deepen understanding and creativity.

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Differentiation Strategies

• For SEND learners:

  • Colour-coded charts with dyslexia-friendly fonts and icons.
  • Simplified instructions, visual step-by-step guides.
  • Peer support and paired work.
  • Short, concise language and repetition of key concepts.

• For advanced learners:

  • Challenge to research and add more substances to the pH scale poster.
  • Encourage scientific explanation for why indicators change colour chemically.

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Assessment

• Formative: Teacher observation during group activity; questioning during plenary.
• Summative: Completed worksheet with correct classification of household substances.
• Self-assessment against success criteria.

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Rosenshine Principles Reflected

• Begin with retrieval of prior knowledge (Do It Now).
• Present new content visually and verbally (dual coding).
• Provide guided practice through demonstration and group activity.
• Check understanding with questioning and plenary.
• Scaffolded practice for diverse learners.
• Independent practice with extension task.

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Reflection Notes for Teachers

• Monitor engagement during practical tasks closely, providing additional scaffolds for SEND.
• Collect worksheets to identify misconceptions for next lesson.
• Use the pH scale poster project to encourage creativity and cross-curricular links with art or literacy.

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This lesson plan ensures practical, accessible, and engaging science learning fully aligned with the National Curriculum whilst adapting to a class with significant SEND representation.