gases in the atmosphere

• Composition of the atmosphere

  • The proportion of gases in the air has not changed much in 200 million years
  • The composition of the atmosphere today is:
  • About four-fifths (approximately 80%) nitrogen
  • about one fifth (approximately 20%) oxygen 
  • small proportions of other gases including carbon dioxide, water vapour and trace quantities of the noble gases
• How can the percentage of oxygen in air be determined?

  By burning phosphorus in air
• What is one method to find the percentage of oxygen in air?

  Reacting a substance with oxygen in air
• Describe the procedure to measure oxygen percentage using phosphorus.

  1. Burn phosphorus in a bell jar.
  2. Place the jar in a water trough.
  3. Ensure initial water levels are equal.
  4. Observe water level rise as oxygen is consumed.
  5. Measure water levels before and after.
• What happens to the water level in the bell jar during the experiment?

  The water level rises as oxygen is used
• Why is phosphorus suitable for measuring oxygen percentage?

  It burns readily until oxygen is depleted
• What is a disadvantage of using phosphorus in this experiment?

  Phosphorus is toxic and hazardous
• What precautions should be taken when handling phosphorus?

  Handle it safely due to its toxicity