Science lesson plan · 7th grade (Year 8 in England) · 45 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 · 5 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.
- Which of these is an alkali (base)? (hydrochloric acid / vinegar / orange juice / sodium hydroxide solution) → sodium hydroxide solutionPrompt: Many alkalis are hydroxides.
- Acids and alkalis: which statement is NOT true? (A pH of 1 is a weak acid. / Strong acids and alkalis can be corrosive, so eye protection is needed. / Alkalis are bases that dissolve in water. / Pure water has a pH of 7.) → A pH of 1 is a weak acid.Prompt: Lower pH means more acidic.
- Which of these is an acid? (soap / lemon juice / pure water / oven cleaner) → lemon juicePrompt: Acids often taste sour (never taste chemicals in the lab!).
Hook · 5 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 · 10 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 · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A solution has a pH of 12. What colour will universal indicator turn? (orange or yellow / red / blue / purple) → purplePrompt: Universal indicator runs like a rainbow from strong acid to strong alkali.
- Why is universal indicator more useful than litmus for comparing two acids? (It only works on acids / It shows a range of colours, so it gives an approximate pH / Litmus does not react with acids / It is always green) → It shows a range of colours, so it gives an approximate pHPrompt: Litmus only has two colours.
You do: independent practice · 10 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 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Why is universal indicator more useful than litmus for comparing two acids? (It shows a range of colours, so it gives an approximate pH / It is always green / Litmus does not react with acids / It only works on acids) → It shows a range of colours, so it gives an approximate pHPrompt: Litmus only has two colours.
- Universal indicator results: lemon juice pH 2, baking soda solution pH 9, vinegar pH 3, oven cleaner pH 13. Which is the most alkaline? (vinegar / lemon juice / baking soda solution / oven cleaner) → 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