Atmospheric Carbon Dioxide

Specification Point 8.21:
  • Explain how the amount of carbon dioxide in the atmosphere was decreased when carbon dioxide dissolved as the oceans formed
  • Carbon dioxide is a water soluble gas (it is the gas used in fizzy drinks) and dissolves readily.
  • When the water vapour condensed large amounts of CO2 dissolved in the oceans.
  • Carbonate substances were precipitated during this process which later formed sediments.
  • This is how the large amounts of carbon dioxide in the early atmosphere was reduced.
  • Nitrogen gas was released by the reaction of ammonia with oxygen and by denitrifying bacteria.
  • The nitrogen was being produced but was not being used up, hence the amount of N2 in the atmosphere increased over time.

Oxygen in the Atmosphere

Specification Point 8.22:
  • Explain how the growth of primitive plants used carbon dioxide and released oxygen by photosynthesis and consequently the amount of oxygen in the atmosphere gradually increased
  • Primitive plants and algae began photosynthesizing which used up more CO2 and released oxygen into the atmosphere:

6CO2 + 6H2O→ C6H12O6 + 6O2

  • Through these processes and over a long period of time, the amount of O2 in the atmosphere has increased and the CO2 decreased, being trapped in fossil fuels and sedimentary rocks.

Test for Oxygen

Specification Point 8.23:
  • Describe the chemical test for oxygen
  • You can check for the presence of oxygen by checking if the gas relights a glowing splint.
  • Insert the glowing splint into the boiling tube and if oxygen gas is present it will relight.

Test for O2, Edexcel GCSE Chemistry

Diagram showing the standard test for oxygen gas which relights a glowing splint

Edexcel GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.