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Science lesson plan · 7th grade (Year 8 in England) · 30 minutes

Read indicator colours to find pH

Chemical reactions, acids and bases

CCSS NGSS.MS-PS1-2CCSS NGSS.SEP 4England: KS3 Chemistry: Acids and alkalis

Objective and success criteria

Students will: Read indicator colours to find pH.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Acids, alkalis (bases) and the pH scale

Leads to: pH and hydrogen ion concentration

Materials: Teacher demo or video, Indicator color chart, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 4 min

  • Quick retrieval from earlier learning (Acids, alkalis (bases) and the pH scale). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Which acid is found in your stomach? (sulfuric acid / nitric acid / hydrochloric acid / citric acid) → hydrochloric acidPrompt: It helps kill bacteria in food.
  2. Acids and alkalis: which statement is NOT true? (Alkalis are bases that dissolve in water. / Pure water has a pH of 7. / Acids have a pH below 7. / Alkalis have a pH below 7.) → Alkalis have a pH below 7.Prompt: Lower pH means more acidic.
  3. Universal indicator turns red in a solution. What does this tell you? (It is pure water / It is a strong alkali / It is a strong acid / It is neutral) → It is a strong acidPrompt: Red is at the low-pH end of the colour chart.

Hook · 3 min

  • Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
  • Share the objective: Read indicator colours to find pH. Read the success criteria together.

I do: model it · 7 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: A solution has a pH of 10. What colour will universal indicator turn?
  • Step 1: pH 10 is alkaline.
  • Step 2: So the answer is: blue
  • Answer: blue
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 6 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. A solution has a pH of 5. What colour will universal indicator turn? (red / green / orange or yellow / purple) → orange or yellowPrompt: Universal indicator runs like a rainbow from strong acid to strong alkali.
  2. Blue litmus paper is dipped into lemon juice. What happens? (It turns purple / It turns green / It stays blue / It turns red) → It turns redPrompt: Lemon juice is acidic.

You do: independent practice · 7 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. A solution has a pH of 8. What colour will universal indicator turn? (red / purple / blue / green) → bluePrompt: Universal indicator runs like a rainbow from strong acid to strong alkali.
  2. Universal indicator results: baking soda solution pH 9, oven cleaner pH 13, milk pH 6, vinegar pH 3. Which is the most alkaline? (baking soda solution / vinegar / oven cleaner / milk) → oven cleanerPrompt: The lower the pH, the more acidic.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Acids, alkalis (bases) and the pH scale.
  • Use concrete materials: teacher demo or video.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Move on to: pH and hydrogen ion concentration.
  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-7.

Free lesson plan from eurekami.com/lesson-plan-builder

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Read indicator colours to find pH

Name

Date

Score/ 6

  1. Question 1

    A solution has a pH of 3. What colour will universal indicator turn?

    • A. blue
    • B. purple
    • C. green
    • D. orange or yellow

  2. Question 2

    Why is universal indicator more useful than litmus for comparing two acids?

    • A. Litmus does not react with acids
    • B. It shows a range of colours, so it gives an approximate pH
    • C. It only works on acids
    • D. It is always green

  3. Question 3

    Universal indicator results: oven cleaner pH 13, baking soda solution pH 9, milk pH 6, lemon juice pH 2. Which is the most acidic?

    • A. oven cleaner
    • B. lemon juice
    • C. baking soda solution
    • D. milk

  4. Question 4

    A solution has a pH of 2. What colour will universal indicator turn?

    • A. green
    • B. purple
    • C. red
    • D. orange or yellow

  5. Question 5

    Blue litmus paper is dipped into lemon juice. What happens?

    • A. It turns red
    • B. It stays blue
    • C. It turns purple
    • D. It turns green

  6. Question 6

    Universal indicator results: soapy water pH 10, milk pH 6, oven cleaner pH 13, pure water pH 7. Which is the most alkaline?

    • A. pure water
    • B. soapy water
    • C. milk
    • D. oven cleaner

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Answer key: Read indicator colours to find pH

  1. 1. D. orange or yellow

  2. 2. B. It shows a range of colours, so it gives an approximate pH

  3. 3. B. lemon juice

  4. 4. C. red

  5. 5. A. It turns red

  6. 6. D. oven cleaner