• 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 / soap / oven cleaner / pure water) → lemon juicePrompt: Acids often taste sour (never taste chemicals in the lab!).
2. Acids and alkalis: which statement is NOT true? (Strong acids and alkalis can be corrosive, so eye protection is needed. / A pH of 1 is a weak acid. / 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.
3. Which acid is found in your stomach? (hydrochloric acid / citric acid / nitric acid / sulfuric acid) → hydrochloric acidPrompt: It helps kill bacteria in food.

• 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 3. What colour will universal indicator turn? (red / blue / orange or yellow / purple) → 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 / colourless / blue / pink) → pinkPrompt: Sodium hydroxide is an alkali.

• 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. A pH meter is better than universal indicator when… (you are testing a solid / the solution is colourless / you want a rainbow of colours / you need a precise numerical pH) → you need a precise numerical pHPrompt: Colours have to be judged by eye.
2. Universal indicator results: soapy water pH 10, vinegar pH 3, pure water pH 7, baking soda solution pH 9. Which is the most acidic? (pure water / soapy water / vinegar / baking soda solution) → vinegarPrompt: The lower the pH, the more acidic.

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