GCSE Chemistry · AQA 8462 · Topic 4.8.2
Identification of common gases
Key points
- Hydrogen: hold a lighted splint at the mouth of the tube. Hydrogen burns rapidly with a squeaky pop.
- Oxygen: put a glowing splint into the tube. Oxygen relights it.
- Carbon dioxide: bubble the gas through limewater (calcium hydroxide solution). Carbon dioxide turns it milky (cloudy).
- Chlorine: hold damp litmus paper in the gas. Chlorine bleaches it white (blue litmus may turn red first).
- Chlorine is toxic, so this test should be done in a fume cupboard.
- Remember the observation, not just the name of the test, as that is what earns marks: 'pop', 'relights', 'milky', 'bleached'.
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Four gases come up again and again in chemistry: hydrogen, oxygen, carbon dioxide and chlorine. Each has a simple test with a clear result, and you must describe both what you do and what you see.
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