What percentage of dry air is nitrogen?

78%. Nitrogen is by far the most common gas in air.

About how much of the air is carbon dioxide?

0.04%. It is a very small fraction, but it matters for the climate.

Air is passed over hot copper until there is no more change. By about how much does its volume fall?

one fifth. The copper reacts with the oxygen, which is about a fifth of the air.

What is the effect of more carbon dioxide in the atmosphere?

global warming. It is a greenhouse gas.

What air is made of · Cambridge IGCSE Chemistry revision

In plain words

Air is a mixture of gases, and it's mostly not the one you breathe for: nearly four fifths is nitrogen, which does nothing for you. About a fifth is oxygen. Everything else, including the carbon dioxide we worry about, adds up to about one part in a hundred.

Three things to know

Dry air is about 78% nitrogen, 21% oxygen, 0.9% argon and 0.04% carbon dioxide.
The percentage of oxygen can be found by using it up: pass air over hot copper, or leave damp iron to rust in it. The volume falls by about one fifth.
Carbon dioxide is a greenhouse gas: it traps heat in the atmosphere. More of it leads to global warming and climate change.

Worked example

100 cm³ of air is passed back and forth over hot copper until the volume stops changing at 79 cm³. Find the percentage of oxygen.

The oxygen has reacted with the copper, so the volume lost is oxygen: 100 − 79 = 21 cm³.
Percentage = 21 ÷ 100 × 100.
= 21%.

Tips and tricks

Nitrogen 78, oxygen 21. Carbon dioxide is tiny: 0.04%, not 4%.
In the oxygen experiments, let the gas cool to room temperature before measuring: hot gas takes up more space.

5 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

What air is made of: 5 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What percentage of dry air is nitrogen?
- 21%
- 50%
- 78% (the answer)
- 99%
Nitrogen is by far the most common gas in air.
Which is the second most common gas in air?
- argon
- carbon dioxide
- oxygen (the answer)
- hydrogen
About 21%.
About how much of the air is carbon dioxide?
- 0.04% (the answer)
- 1%
- 4%
- 21%
It is a very small fraction, but it matters for the climate.
Air is passed over hot copper until there is no more change. By about how much does its volume fall?
- one tenth
- one fifth (the answer)
- one half
- four fifths
The copper reacts with the oxygen, which is about a fifth of the air.
What is the effect of more carbon dioxide in the atmosphere?
- acid rain
- holes in the ground
- global warming (the answer)
- more oxygen
It is a greenhouse gas.

5 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

3 questions, 7 marks. Write your answers on paper, then check them.

What air is made of

Cambridge IGCSE Chemistry 0620 · 7 marks · papermunch.org

Name ______________________________ Date ______________

State the percentages of nitrogen and oxygen in dry air.[2]
Show answerHide answer
About 78% nitrogen and 21% oxygen.
I got this one
50 cm³ of air is left over damp iron wool until the volume stops changing at 39.5 cm³. Calculate the percentage of oxygen in the air.[3]
Show answerHide answer
21%. Oxygen used = 50 − 39.5 = 10.5 cm³; 10.5 ÷ 50 × 100.
I got this one
Explain why carbon dioxide is described as a greenhouse gas.[2]
Show answerHide answer
It absorbs heat (infrared radiation) given off by the Earth and so keeps the atmosphere warm.
I got this one

Answers: What air is made of

1. About 78% nitrogen and 21% oxygen.
2. 21%. Oxygen used = 50 − 39.5 = 10.5 cm³; 10.5 ÷ 50 × 100.
3. It absorbs heat (infrared radiation) given off by the Earth and so keeps the atmosphere warm.