Contents
Independent final check
Explain without the key
deduce / explain
Final check
Calcium carbonate is a white solid. A lump of it is heated very strongly for ten minutes. The gas given off turns limewater milky. When the lump is cold, it still looks white. (a) Identify the gas, and explain why the limewater result proves that a new substance was made. (b) A few drops of water are added to the cold lump. It hisses, gives off steam and crumbles into a powder. Drops of water on a lump of calcium carbonate do nothing. Explain what this shows about the solid left after heating.
deduce: reach a conclusion from the information given. explain: give reasons and connect them to evidence.
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Scope and sources
Cambridge IGCSE Chemistry 0620 · 2026–2028 v2 · Original learning materials.
Physical and chemical changes (6.1 Core 1): identifying physical and chemical changes and describing the difference in terms of whether any new substances have been made. Rates of reaction are in the next module, reversible reactions in 6.3 and the tests for gases in topic 12.
Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.
Official Cambridge syllabus