Who this is for: Cambridge IGCSE Chemistry (0620) students who want air — composition, fractional distillation and uses of gases — to become structured answers instead of approximate percentages they half-remember.
What query it owns: how to understand and revise air in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the air revision-guide angle, while Tutopiya’s Air subtopic page owns the learning resource and the free Air quiz owns the practice.

Air is a foundation topic in the Chemistry Of The Environment unit of Cambridge IGCSE Chemistry (0620). Examiners expect you to state the composition of clean dry air, describe fractional distillation of liquid air, and give uses of nitrogen, oxygen and noble gases. This guide organises each gas with its industrial use and the question types that appear every year.

Key takeaways

• Clean dry air is approximately 78% nitrogen, 21% oxygen and 1% argon (plus trace gases).
• Fractional distillation of liquid air separates gases by boiling point — nitrogen boils off first (−196 °C), then oxygen (−183 °C).
• Nitrogen is unreactive — used to make ammonia and as an inert atmosphere in food packaging.
• Oxygen supports combustion and respiration — used in steelmaking and hospitals.
• Argon and other noble gases are inert — used in light bulbs and welding.

What is air in Cambridge IGCSE Chemistry?

Air chemistry at IGCSE covers the percentage composition of the atmosphere, how industrial gases are separated from liquid air, the uses of each major component, and how air pollution (especially carbon dioxide) links to climate change. You must distinguish clean dry air from polluted air.

Read the full notes on Tutopiya’s Air subtopic page before attempting questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Composition	78% N₂, 21% O₂, 1% Ar	”State the percentage of nitrogen in air.”
Fractional distillation	Separate by boiling point at low temperature	”Describe how oxygen is obtained from air.”
Uses of N₂	Ammonia, inert atmosphere, food packaging	”Give a use of nitrogen.”
Uses of O₂	Combustion, respiration, steelmaking	”State a use of oxygen.”
Noble gases	Unreactive — lamps, welding shields	”Explain why argon is used in lamps.”

How to describe fractional distillation of air — step by step

1. Air is filtered to remove dust and compressed.
2. Cooled to very low temperature — air becomes a liquid.
3. Fractional distillation column — nitrogen boils off first (lower boiling point).
4. Oxygen collected at a higher temperature fraction.
5. Argon and other gases collected separately.
6. Link separation to differences in boiling points.

Test yourself with the free Air quiz.

Composition vs separation vs uses: which does the question want?

Situation	What to write	Typical signal words
Percentages	78% N₂, 21% O₂, 1% Ar	”composition of clean dry air”
Industrial separation	Fractional distillation of liquid air	”how oxygen is obtained”
Gas uses	Named use linked to property	”use of nitrogen in food packaging”
Pollution	Rising CO₂, greenhouse effect	”how air composition is changing”

Air in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical air stem
State	Percentage or named gas	”State the percentage of oxygen in air.”
Describe	Fractional distillation process	”Describe how nitrogen is separated from air.”
Give / State a use	Industrial or everyday application	”Give one use of argon.”
Explain	Why a gas is suitable for a use	”Explain why nitrogen is used in crisp packets.”
Compare	Clean air vs polluted air	”Compare the composition of clean and polluted air.”

Worked exam-style stems (how to answer the wording)

1. “State the percentage composition of oxygen and nitrogen in clean dry air.” Oxygen: 21%; Nitrogen: 78%. Reward: both correct.
2. “Describe how oxygen is obtained from the air on an industrial scale.” Air is compressed and cooled to form liquid air. Fractional distillation separates gases by boiling point — oxygen is collected at −183 °C (after nitrogen has boiled off). Reward: liquefaction + fractional distillation + boiling point difference.
3. “Explain why nitrogen is used to fill crisp packets.” Nitrogen is unreactive (inert), so it prevents oxidation of the crisps and keeps them fresh. Reward: unreactive + prevents oxidation.

When you can recognise the wording instantly, work through the Air quiz and Carbon Dioxide And Methane for pollution links.

How air connects to the rest of the environment unit

Air links to Carbon Dioxide And Methane (greenhouse gases), Sulfur (acid rain gases) and Water (dissolved gases). The Cambridge IGCSE Chemistry resource hub links every environment subtopic.

Common mistakes students make

• Swapping 78% and 21% for nitrogen and oxygen.
• Describing fractional distillation without mentioning boiling points.
• Saying oxygen is obtained by filtering air — it requires liquefaction and distillation.
• Forgetting argon (~1%) in composition questions.
• Confusing nitrogen’s unreactivity with noble gas inertness — nitrogen still forms compounds industrially.

When you need more support

If air composition or fractional distillation questions keep losing marks, work through the Air quiz, then get focused help from a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

What is the composition of clean dry air? Approximately 78% nitrogen, 21% oxygen and 1% argon, with small amounts of carbon dioxide and other trace gases.

How is oxygen separated from air industrially? Air is compressed, cooled to a liquid and fractionally distilled. Gases are separated by differences in boiling point.

Why is nitrogen used in food packaging? It is unreactive and prevents oxidation, keeping food fresh for longer.

How do I revise air effectively? Memorise percentages, practise a fractional distillation description, list one use per gas, then take the Air quiz.

Ready to master Cambridge IGCSE Chemistry air?

Start with the Air subtopic page, then book a free trial with a Cambridge IGCSE Chemistry specialist to turn air chemistry into guaranteed marks.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial