• Quick retrieval from earlier learning (What acids make with metals and carbonates). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Magnesium reacts with sulfuric acid. What are the products? (magnesium oxide + hydrogen / magnesium sulfate + hydrogen / magnesium sulfate + carbon dioxide / magnesium chloride + hydrogen) → magnesium sulfate + hydrogenPrompt: acid + metal → salt + hydrogen
2. Copper carbonate reacts with sulfuric acid. What are the products? (copper oxide + carbon dioxide / copper sulfate + water + carbon dioxide / copper sulfate + water / copper carbonate + water) → copper sulfate + water + carbon dioxidePrompt: Carbonates fizz with acids. Which gas turns limewater cloudy?
3. How could you prove that the gas from magnesium and acid is hydrogen? (it relights a glowing splint / it bleaches damp litmus / it turns limewater cloudy / a lighted splint gives a squeaky pop) → a lighted splint gives a squeaky popPrompt: Hydrogen burns rapidly with oxygen.

• Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
• Share the objective: Identify gases with laboratory tests. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Which gas gives this result: bubbled through limewater, it turns it milky?
• Step 1: Carbon dioxide turns limewater milky (cloudy).
• Step 2: So the answer is: carbon dioxide
• Answer: carbon dioxide
• 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. Which gas gives this result: damp litmus paper is bleached white? (hydrogen / oxygen / carbon dioxide / chlorine) → chlorinePrompt: Each common gas has its own test.
2. Why must the chlorine test be done in a fume cupboard? (Chlorine is toxic / Chlorine is invisible / Chlorine explodes / Chlorine is radioactive) → Chlorine is toxicPrompt: Think about safety.

• 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 gas gives this result: damp litmus paper is bleached white? (hydrogen / oxygen / carbon dioxide / chlorine) → chlorinePrompt: Each common gas has its own test.
2. Tests for gases: which statement is NOT true? (Hydrogen gives a squeaky pop with a lighted splint. / Oxygen relights a glowing splint. / Chlorine may turn damp blue litmus red before bleaching it. / Chlorine turns limewater milky.) → Chlorine turns limewater milky.Prompt: Which gas pops and which relights a splint?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-9.