IGCSE Chemistry Guide: Air Water Quality Revision
Talimat Academic Team
Education Specialist
IGCSE Chemistry air and water covers clean air composition, pollutants, pollution control, greenhouse gases, water tests, and water treatment. It is now examined under Topic 10, Chemistry of the environment, once labelled Topic 11. The content itself stays almost the same.
Many students revise air and water from old Topic 11 notes, then get confused by the renumbered syllabus. This guide gives a version-accurate summary of every examinable point, plus the exact tests examiners reward.
It sits within the wider IGCSE curriculum you are studying.
What does IGCSE Chemistry air and water cover?
IGCSE Chemistry air and water covers six examinable strands: clean air composition, air pollutants, pollution control, greenhouse gases, water tests, and water treatment.
Clean, dry air is mostly nitrogen and oxygen. Small amounts of argon and carbon dioxide make up the rest.
- Nitrogen: about 78 percent
- Oxygen: about 21 percent
- Argon and other noble gases: about 1 percent
- Carbon dioxide: about 0.04 percent
Core students learn the main ideas here. Extended students add symbol equations, such as the reactions inside a catalytic converter. Both routes share the same six strands, so start with the map above.
Is it still Topic 11?
No. In the current 2023 to 2025 and 2026 to 2028 syllabus, this content sits under Topic 10, Chemistry of the environment. Topic 11 is now Organic Chemistry. So "IGCSE chemistry topic 11" points to the older, pre-2023 layout.
According to Cambridge Assessment International Education, the 0620 syllabus keeps the same subject content but renumbers its topics. This is good news.
Your pre-2023 notes are still valid on the actual chemistry, just filed under a new number. The 0620 grade scale and the 0971 nine-to-one scale share identical content too.
If you want to see how this fits the whole course, our IGCSE Chemistry tutors map every topic for you.
How do you test water and its purity?
Two chemical tests show that water is present. Anhydrous copper(II) sulfate turns from white to blue. Anhydrous cobalt(II) chloride turns from blue to pink. To confirm purity, you check the boiling point and melting point instead.
These two reagents confirm that a liquid contains water. Watch the colour change closely, because examiners often ask you to name both the reagent and the exact colours before and after.
| Test | What it checks | Result for pure water |
|---|---|---|
| Anhydrous copper(II) sulfate | Shows water is present | White solid turns bright blue |
| Anhydrous cobalt(II) chloride | Shows water is present | Blue solid turns pale pink |
| Boiling point | Shows the water is pure | Boils at exactly 100 °C |
| Melting point | Shows the water is pure | Freezes at exactly 0 °C |
Distilled water is used in experiments because tap water contains dissolved salts. Those salts change the boiling point, so results would no longer be reliable.
How water treatment works
Water treatment chemistry cleans raw water in stages. First, sedimentation and filtration remove solid bits. Next, carbon removes bad taste and smell. Finally, chlorination kills harmful bacteria and microbes, so the water becomes safe to drink.
Follow these treatment stages in the correct order, because exam questions often test the sequence and the job of each step.
- Sedimentation: solids sink and settle out
- Filtration: sand beds trap smaller particles
- Carbon treatment: removes taste and odour
- Chlorination: kills bacteria and microbes
Water is also vital at home and in industry, working as both a solvent and a coolant.
Process questions like these trip up many students. Working through them with a specialist IGCSE Chemistry tutor can turn confusion into easy marks.
Air pollutants and their effects
Air quality revision for IGCSE focuses on four main pollutants. Carbon monoxide comes from incomplete combustion and is toxic. Sulfur dioxide and oxides of nitrogen cause acid rain and harm breathing. Particulates, tiny bits of soot, also damage the lungs.
According to the World Health Organization, air pollution is linked to about 7 million premature deaths worldwide each year. That single figure shows why examiners care about this topic.
This table pairs each pollutant with its main source and its harmful effect. Learn all three columns together, since a single exam question can ask you to link a pollutant to both.
| Pollutant | Main source | Harmful effect |
|---|---|---|
| Carbon monoxide | Incomplete combustion of fuels | Toxic, reduces oxygen carried in blood |
| Sulfur dioxide | Sulfur burning inside fuels | Acid rain and breathing problems |
| Oxides of nitrogen | Hot car engines | Acid rain and breathing problems |
| Particulates | Soot from combustion | Damage lungs and worsen asthma |
Notice that sulfur dioxide and nitrogen oxides share effects. Both dissolve in rain to form acid rain, which damages plants, lakes, and buildings.
Oxides of nitrogen form when nitrogen and oxygen react in the heat of a car engine. You can go deeper with IGCSE Environmental Management support.
How to reduce air pollution
You can cut air pollution in a few clear ways. Catalytic converters change carbon monoxide and nitrogen oxides into carbon dioxide and nitrogen. Flue gas desulfurisation removes sulfur dioxide from power stations. Using less fossil fuel lowers every combustion pollutant at once.
Match each control method to the pollutant it targets, a favourite pairing in exams.
- Catalytic converter: removes carbon monoxide and nitrogen oxides
- Flue gas desulfurisation: removes sulfur dioxide
- Burning less fossil fuel: lowers all pollutants
Extended students should also learn the symbol equations for these reactions. Write them out until they feel automatic. Timed practice on real questions locks the method in.
Which gases cause the greenhouse effect?
In IGCSE Chemistry air and water, two greenhouse gases matter most. Carbon dioxide comes from combustion and respiration. Methane comes from rotting vegetation and from digestion in animals like cattle. Both gases trap heat near the surface.
That trapped heat drives global warming and climate change. Keep your answer at syllabus depth. Name the two gases, state their sources, and link them to a warmer planet. That level of detail is enough for full marks.
Key takeaways and next steps
Here is your quick recap of IGCSE Chemistry air and water. Clean air is mostly nitrogen and oxygen. Pollutants such as carbon monoxide and sulfur dioxide harm health, while control methods and cleaner fuels cut them down.
Carbon dioxide and methane drive the greenhouse effect. Water tests confirm both presence and purity. Treatment then makes water safe to drink. Remember too that this content is now Topic 10, once labelled Topic 11.
Ready for your next step? Download a topic revision checklist, then drill real exam questions on our past papers page. Practice under timed conditions is what turns these notes into marks.
Frequently Asked Questions
Rusting needs both water and oxygen, so students often expect it here. In the current syllabus, rusting sits under Topic 9, Metals, not under the environment topic.
Sulfur dioxide and oxides of nitrogen dissolve in rainwater. This forms weak acids that fall as acid rain and slowly damage the environment.
Tap water holds dissolved salts that shift its boiling and melting points. Distilled water is pure, so your results stay reliable and repeatable.
Place a glowing splint into the gas. If the splint relights, the gas is oxygen. Students often mix this up with the water tests.
Both. Core students learn the main ideas. Extended students add symbol equations, such as the reactions inside a catalytic converter.
About the author
Talimat Academic Team
Education Specialist
The Talimat Academic Team are Cambridge-trained British educators with extensive experience teaching IGCSE and A-Level across the GCC.
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