• Quick retrieval from earlier learning (Conservation of mass in reactions). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. In a sealed flask, 29 g of substance A reacts completely with 20 g of substance B. 5 g of product D forms along with product C. What mass of C forms, in g? → 44 gPrompt: Total mass of reactants = total mass of products.
2. 25 g of calcium carbonate is heated in an open tube until it all breaks down. 14 g of calcium oxide is left. What mass of carbon dioxide escaped, in g? → 11 gPrompt: Mass seems to be lost. Where did it go?
3. Magnesium ribbon is burned in a crucible. The ash weighs more than the ribbon did. Why? (Heat has mass / Burning creates new atoms / Oxygen atoms from the air have combined with the magnesium / The crucible got heavier) → Oxygen atoms from the air have combined with the magnesiumPrompt: What is the product of burning magnesium?

• Drop an antacid tablet in water (or show a clip) and ask whether a new substance is being made.
• Share the objective: Thermal decomposition of carbonates. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Calcium carbonate is heated strongly and breaks down. What are the products?
• Step 1: metal carbonate → metal oxide + carbon dioxide
• Step 2: So the answer is: calcium oxide + carbon dioxide
• Answer: calcium oxide + 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. Zinc carbonate is heated strongly and breaks down. What are the products? (zinc oxide + oxygen / zinc + carbon dioxide / zinc hydroxide + water / zinc oxide + carbon dioxide) → zinc oxide + carbon dioxidePrompt: A carbonate contains a metal, carbon and oxygen.
2. Green copper carbonate is heated and turns black. What is the black solid? (copper sulfate / carbon / copper oxide / copper) → copper oxidePrompt: Carbon dioxide has left the solid.

• 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. Copper carbonate is heated strongly and breaks down. What are the products? (copper hydroxide + water / copper + oxygen + carbon / copper oxide + carbon dioxide / copper + carbon dioxide) → copper oxide + carbon dioxidePrompt: A carbonate contains a metal, carbon and oxygen.
2. How can you show that carbon dioxide is given off when a carbonate is heated? (hold a glowing splint in it, which relights / bubble the gas through limewater, which turns cloudy (milky) / smell it / hold a lit splint in it, which gives a squeaky pop) → bubble the gas through limewater, which turns cloudy (milky)Prompt: This test is specific to carbon dioxide.

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