Percentage of Oxygen in Air

We have read that Air consists mainly of molecules of oxygen and nitrogen with important yet trace amounts of other gases.

We know that the combustion of organic material requires oxygen.

The idea here is to capture a quantity of air in a measured and isolated volume and then use up all the oxygen by burning something.

The remaining volume will be mostly molecular nitrogen.

Equipment needed

  1. flasks
  2. water container
  3. candles
  4. rulers
  5. thermometer


  1. The volume of a flask is measured.
  2. Water is placed in a container along with a thermometer, and a flask inverted over a lit candle resting in the water. Eventually the candle goes out.
  3. Measure the height of water relative to the original water height. Calculate the volume.
  4. From the total volume, assumed to be oxygen and nitrogen, compute the percentage of oxygen.


Suppose the heights of air were measured before and after several days and the following measurements were made

Height of air at the start of experiment = 100cm

Height of air after several days = 80cm

Percentage oxygen in the air = Change in volume of air X 100%

Total volume of air

= 100cm – 80cm X 100%


= 20%

The approximate composition of the air today is

The proportion of carbon dioxide in the air has risen from 0•03% to 0•04% in the last hundred years due to the burning of fossil fuels.

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