i/GCSE Chemistry – Gases in the air

Chemistry Section 6


2.9
- Gases in the atmosphere and their percentages:
- Nitrogen - 78%
- Oxygen - 21%
- Argon - 0.96%
- Carbon dioxide - 0.035
- Water vapour and other gases - 0.005%


2.10
- Calculating percentage volume of oxygen using metal (iron):
- Place wet iron filings at the end of a burette
- Use a clamp to hold the burette vertically in the trough of water
- Measure and note the starting height of the water level in the
burette
- Measure starting height of the water level in the burette
- Leave apparatus for weeks
- Measure final height of the water in the burette
- After a few days, the iron filings will react with the oxygen (iron
oxide) and the water will rise to replace the oxygen
- E.g. water level was 15cm2 and is now 12cm2 so 3cm2 was used up
- % O2 = (xcm3 of O2 / xcm3 of original air) x 100
- E.g. (3cmcm2) x 100 = 20% oxygen
- Calculating percentage volume of oxygen using nonmetals (phosphorus):
- Add phosphorus onto an evaporating dish and place it on a trough of
water, making sure it is floating
- Ignite phosphorus with a candle
- Cover with a bell jar
- Measure starting height of water level in bell jar
- Leave apparatus for several days
- Measure the final height of water in bell jar