• 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. Universal indicator turns red in a solution. What does this tell you? (It is pure water / It is a strong alkali / It is a strong acid / It is neutral) → It is a strong acidPrompt: Red is at the low-pH end of the colour chart.
2. Acids and alkalis: which statement is NOT true? (Acids have a pH below 7. / Pure water has a pH of 7. / Strong acids and alkalis can be corrosive, so eye protection is needed. / Alkalis have a pH below 7.) → Alkalis have a pH below 7.Prompt: Lower pH means more acidic.
3. Which acid is found in your stomach? (nitric acid / citric acid / hydrochloric 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? (green / orange or yellow / blue / purple) → orange or yellowPrompt: Universal indicator runs like a rainbow from strong acid to strong alkali.
2. Blue litmus paper is dipped into lemon juice. What happens? (It turns green / It turns red / It turns purple / It stays blue) → It turns redPrompt: Lemon juice is acidic.

• 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: oven cleaner pH 13, milk pH 6, pure water pH 7, lemon juice pH 2. Which is the most acidic? (pure water / milk / lemon juice / oven cleaner) → lemon juicePrompt: The lower the pH, the more acidic.
2. Blue litmus paper is dipped into lemon juice. What happens? (It turns purple / It turns red / It turns green / It stays blue) → It turns redPrompt: Lemon juice is acidic.

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