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What is the troposphere?
The troposphere is a layer of the atmosphere where we live and it extends to appoximately 10km above the surface of the earth
What is the percentage composition of gases in troposphere
Nitrogen - 78%
Oxygen - 21%
Argon - 1%
Other gases - 1% (including carbon dioxide 0.04%)
What 2 experiments can you do to show the percentage of oxygen in the atmosphere?
Reaction with copper
Reaction with iron (or phosphorus)
Describe the reaction with copper
The 100 cm3 of air can be pushed from one syringe into the other without any change in volume.
When the copper is heated and the air pushed from one syringe to the other, the orange copper reacts with the oxygen to form black copper(II) oxide. The volume of air decreases as the oxygen is removed.
Once all the oxygen has reacted and some copper remains unreacted and the apparatus allowed to cool, the final volume of air is 79 cm3.

Describe the reaction with iron (or phosphorus)
As the damp iron wool reacts with oxygen from the air, the iron rusts, the oxygen is removed and the water rises up the measuring cylinder to replace the 'lost' oxygen.
Example results:
Volume of air | cm3 |
Start | 94 |
After a few days | 73.5 |
Volume of air removed = 94 - 73.5 = 20.5 cm3
Percentage of oxygen = (20.5/94) x 100 = 21.8 %
