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GCSE Chemistry · key term
A gas that supports combustion and makes a glowing splint relight.
Used by Edexcel and OCR
Specification 8.23 · Paper 2
Revise: Chemical Test for OxygenOxygen is a gas that supports combustion. This gives us a way to identify it: a wooden splint that is still glowing, but no longer flaming, will relight when it is placed in oxygen.
Specification C6.3b · Paper 2 (Foundation), Paper 4 (Higher)
A gas made of molecules containing two oxygen atoms; it is released during photosynthesis and makes up about one-fifth of today's atmosphere.
Revise: Oxygen DevelopmentThe Earth's early atmosphere is thought to have contained little or no oxygen. Today's air is very different: roughly one-fifth of it is oxygen. That change took place gradually over billions of years, rather than when the atmosphere first formed.
State both the method and the positive result: a glowing splint relights in oxygen.
Describe a sequence: little oxygen in the early atmosphere; algae photosynthesised; plants appeared later; oxygen gradually built up.
Do not say that volcanoes produced the oxygen-rich atmosphere. Photosynthesis was the main source of the increase.
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