• Quick retrieval from earlier learning (Physical and chemical changes). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Is this a physical or a chemical change: wood burning? (physical change / chemical change) → chemical changePrompt: Is a new substance made?
2. A nail left outside turns orange-brown and flaky. What has happened? (The nail melted / Iron reacted with oxygen and water to make rust / Paint fell on it / The nail dissolved) → Iron reacted with oxygen and water to make rustPrompt: Rusting needs both air and water.
3. Physical and chemical changes: which statement is NOT true? (Dissolving is a physical change. / Burning is a chemical change. / All bubbles mean a chemical reaction. / Rusting needs both oxygen and water.) → All bubbles mean a chemical reaction.Prompt: Does each change make a new substance?

• Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
• Share the objective: Acids, alkalis (bases) and the pH scale. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Universal indicator turns red in a solution. What does this tell you?
• Step 1: Red means pH about 0–2: strongly acidic. Green is neutral; purple is strongly alkaline.
• Step 2: So the answer is: It is a strong acid
• Answer: It is a strong acid
• 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. What happens to blue litmus paper in an acid? (It turns red / It turns purple / It stays blue / It turns green) → It turns redPrompt: Litmus has only two colours.
2. Acids and alkalis: which statement is NOT true? (Alkalis have a pH below 7. / Strong acids and alkalis can be corrosive, so eye protection is needed. / Acids have a pH below 7. / Alkalis are bases that dissolve in water.) → Alkalis have a pH below 7.Prompt: Lower pH means more 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 8 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. Which of these is an alkali (base)? (hydrochloric acid / orange juice / vinegar / sodium hydroxide solution) → sodium hydroxide solutionPrompt: Many alkalis are hydroxides.
2. Acids and alkalis: which statement is NOT true? (Strong acids and alkalis can be corrosive, so eye protection is needed. / Acids have a pH below 7. / Pure water has a pH of 7. / Alkalis have a pH below 7.) → Alkalis have a pH below 7.Prompt: Lower pH means more acidic.

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