The combustion of elements in oxygen
2 marks · EasyA student burns phosphorus in a bell jar containing 300 cm³ of air. After the reaction, the water level inside the bell jar rises by 63 cm³. Calculate the percentage of oxygen in air, based on these results. Give your answer to the nearest whole number.
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21 % (±1)
Also accept: 21%
Common mistakes: Using incorrect total volume
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Marking points
M1 · 1 mark · Uses the formula: (rise in water / original air volume) × 100
A1 · 1 mark · Correctly calculates 21% (accept 21 or 21%)
Worked solution
Percentage of oxygen = (rise in water/original air volume) × 100