• 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? (lemon juice / pure water / 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. / Acids have a pH below 7. / Strong acids and alkalis can be corrosive, so eye protection is needed. / All acids are dangerous.) → All acids are dangerous.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 neutral / It is a strong alkali / It is a strong acid) → It is a strong acidPrompt: Red is at the low-pH end of the colour chart.

• 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 9. What colour will universal indicator turn? (green / red / purple / blue) → bluePrompt: 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 only works on acids / It is always green / 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. Blue litmus paper is dipped into lemon juice. What happens? (It stays blue / It turns red / It turns purple / It turns green) → It turns redPrompt: Lemon juice is acidic.
2. Universal indicator results: pure water pH 7, oven cleaner pH 13, lemon juice pH 2, soapy water pH 10. Which is the most alkaline? (lemon juice / soapy water / oven cleaner / pure water) → oven cleanerPrompt: The lower the pH, the more acidic.

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