Showing that air contains about one-fifth oxygen

2 marks · Hard

Name the two most abundant gases in dry, unpolluted air. State their approximate percentage composition by volume for each gas.

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

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Nitrogen (about 78%), Oxygen (about 21%)

Also accept: Nitrogen (about 78%) and Oxygen (about 21%); Nitrogen (78%) and Oxygen (21%); Nitrogen (78.1%) and Oxygen (21.0%); N2 (78%), O2 (21%)

Common mistakes: Reversing percentage values; Including argon or CO2 as most abundant

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Marking points

B1 · 1 mark · Names both nitrogen and oxygen as most abundant gases (any order).

B2 · 1 mark · Gives correct percentage for each: nitrogen (about 78%), oxygen (about 21%). Accept small rounding.

Worked solution

The most abundant gases in dry, unpolluted air are nitrogen and oxygen.

Nitrogen makes up about 78% of dry air, and oxygen makes up about 21%.