The combustion of elements in oxygen

2 marks · Easy

During the combustion of phosphorus in air, a student measures that the water level in the bell jar rises by 44 mL. The total original air volume in the jar was 210 mL. Calculate (to the nearest whole number) the percentage of oxygen in the original air sample.

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21 % (±1)

Common mistakes: forgets to multiply by 100; incorrect division

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Correctly sets up calculation: (change in volume/total volume) × 100 (follow-through)

A1 · 1 mark · Calculates correct answer: 21 (%) to nearest whole number (follow-through)

Worked solution

Percentage of oxygen = (Volume rise / Total air volume) × 100