Specification Point 2.10:
Understand how to determine the percentage by volume of oxygen in air using experiments involving the reactions of Metals (E.g. Iron) and non-metals (E.g. Phosphorus) with Air
Specification Point 2.14:
Practical: Determine the approximate percentage by volume of Oxygen in air using Metal or Non-Metal

Calculating Oxygen Volume with Metals

Percentage volume of O2 in air, Edexcel IGCSE Chemistry

Use of Iron to calculate percentage volume of Oxygen in Air

Method:

  • Place wet iron filings at the end of a burette (use Vaseline if iron filings do not stick)
  • 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
  • Leave apparatus for weeks
  • Measure and note the final height of the water level in the burette

Results:

  • After several days, the water will rise up the burette and reach a constant level as the iron filings will react with all the oxygen in the air to form iron(III) oxide (rust).
  • The water level will rise to replace the volume of oxygen lost during this reaction.
  • E.g. the original water levels was 15 cm2 and is now 12 cm2. 3 cm2 has been used up.

3/15 x 100 = 20% Oxygen in air

Calculations:

Volume of Air at the Start = ( Total Burette Volume – Initial Burette Reading)

Volume of Oxygen Used (Reacted with Iron) = ( Initial Reading – Final Reading )

Percentage Volume of Oxygen Calculation:

Equation for calculating O2 volume, Edexcel IGCSE Chemistry

Calculating Oxygen Volume with Non-Metals

Calculating O2 with non-metals, Edexcel IGCSE Chemistry

Use of Phosphorus to calculate percentage volume of Oxygen in Air

Method:

  • Add Phosphorus onto an evaporating dish and place it on a trough of water, making sure it is floating
  • Ignite Phosphorus using a candle
  • Cover this with a bell jar
  • Measure and note the starting height of the water level in the bell jar
  • Leave apparatus for several days
  • Measure and note the final height of the water level in the bell jar

Results:

  • After several days, the water will rise up the bell jar and reach a constant level as the Phosphorus will use up Oxygen in the air in order to burn (air is one of the three elements that a fire needs)
  • The water level will rise to replace the volume of Oxygen lost during this reaction

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Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.