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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 of these is an acid? (pure water / lemon juice / oven cleaner / soap) → lemon juicePrompt: Acids often taste sour (never taste chemicals in the lab!).
  2. Acids and alkalis: which statement is NOT true? (Alkalis are bases that dissolve in water. / Strong acids and alkalis can be corrosive, so eye protection is needed. / Acids have a pH below 7. / All acids are dangerous.) → All acids are dangerous.Prompt: Lower pH means more acidic.
  3. What happens to blue litmus paper in an acid? (It stays blue / It turns red / It turns green / It turns purple) → It turns redPrompt: Litmus has only two colours.

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 1. What colour will universal indicator turn? (blue / green / red / orange or yellow) → redPrompt: Universal indicator runs like a rainbow from strong acid to strong alkali.
  2. Phenolphthalein is added to sodium hydroxide solution. What colour does it go? (blue / colourless / yellow / pink) → pinkPrompt: Sodium hydroxide is an alkali.

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 6. What colour will universal indicator turn? (red / purple / orange or yellow / blue) → orange or yellowPrompt: Universal indicator runs like a rainbow from strong acid to strong alkali.
  2. Phenolphthalein is added to sodium hydroxide solution. What colour does it go? (yellow / pink / colourless / blue) → pinkPrompt: Sodium hydroxide is an alkali.

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

    Universal indicator results: baking soda solution pH 9, milk pH 6, lemon juice pH 2, soapy water pH 10. Which is the most alkaline?

    • A. lemon juice
    • B. baking soda solution
    • C. soapy water
    • D. milk

  2. Question 2

    Phenolphthalein is added to sodium hydroxide solution. What colour does it go?

    • A. pink
    • B. yellow
    • C. blue
    • D. colourless

  3. Question 3

    A solution has a pH of 13. What colour will universal indicator turn?

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

  4. Question 4

    Universal indicator results: pure water pH 7, lemon juice pH 2, milk pH 6, oven cleaner pH 13. Which is the most alkaline?

    • A. lemon juice
    • B. pure water
    • C. oven cleaner
    • D. milk

  5. Question 5

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

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

  6. Question 6

    A solution has a pH of 9. What colour will universal indicator turn?

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

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Answer key: Read indicator colours to find pH

  1. 1. C. soapy water

  2. 2. A. pink

  3. 3. A. purple

  4. 4. C. oven cleaner

  5. 5. C. It shows a range of colours, so it gives an approximate pH

  6. 6. A. blue