• 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 alkali (base)? (hydrochloric acid / vinegar / sodium hydroxide solution / orange juice) → sodium hydroxide solutionPrompt: Many alkalis are hydroxides.
2. Acids and alkalis: which statement is NOT true? (All acids are dangerous. / Pure water has a pH of 7. / Strong acids and alkalis can be corrosive, so eye protection is needed. / Alkalis are bases that dissolve in water.) → All acids are dangerous.Prompt: Lower pH means more acidic.
3. What happens to blue litmus paper in an acid? (It turns red / It stays blue / It turns purple / It turns green) → It turns redPrompt: Litmus has only two colours.

• 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.

• 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.

• 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 13. What colour will universal indicator turn? (blue / orange or yellow / green / purple) → purplePrompt: Universal indicator runs like a rainbow from strong acid to strong alkali.
2. Why is universal indicator more useful than litmus for comparing two acids? (Litmus does not react with acids / It is always green / It only works on acids / It shows a range of colours, so it gives an approximate pH) → It shows a range of colours, so it gives an approximate pHPrompt: Litmus only has two colours.

• 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.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. Universal indicator results: milk pH 6, baking soda solution pH 9, lemon juice pH 2, vinegar pH 3. Which is the most alkaline? (vinegar / milk / baking soda solution / lemon juice) → baking soda solutionPrompt: The lower the pH, the more acidic.
2. A solution has a pH of 4. What colour will universal indicator turn? (orange or yellow / green / purple / red) → orange or yellowPrompt: Universal indicator runs like a rainbow from strong acid to strong alkali.

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