2.17 explain how experiments involving the reactions of elements such as copper, iron and phosphorus with air can be used to investigate the percentage by volume of oxygen in air

There are several ways to conduct this experiment –

1. Using Copper Turnings

  1. Set up apparatus with 100cm³ of air in one of the syringes
  2. Heat the copper turnings using a blue bunsen flame
  3. Pass the air backwards and forwards over the coppper
  4. Stop heating when the volume of gas in the syringe stops decreasing (

    copper + oxygen →copper oxide = 2Cu(s) + O2(g) → 2CuO(s) the 2CuO is black, oxidised copper)

  5. Final volume will be 79cm³, which shows that 21cm³ of air has been used up -therefore proving that 21% of the air is oxygen large.png

 

2. Using Iron (by rusting)

  1. Place damp iron wool/filings at the end of an upturned test tube and set up apparatus
  2. Over a set period of days the iron will react with the oxygen and reach a constant level
  3. Do these 3 equations to determine the oxygen level :
  • Volume of air at the start = 50- initial test tube reading
  • Volume of oxygen used = Initial reading – final reading
  • Percentage of oxygen used = (volume of oxygen used / volume of air at the start ) x 100

Note – the reason why I have put 50 – initial test tube reading (first bullet point) is that in class I used a burette as it measures the volumes more precisely. You should use the largest integer on your measuring equipment (the max amount it can hold) to gage the volume of air at the start. Rust

3. Using Phosphorus

  1. Equalise the levels of water inside and outside of the bell jar
  2. Touch the phosphorus with a metal rod
  3. Phosphorus will burn, levels in the bell jar will rise and the phosphorus will stop burning
  4. Measure the change in levels
  5. Equation: 4P (s) + 5O2 (g) → 2P2O2(s)

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