IGCSE Chemistry Chemistry in Society Notes
This unit connects chemistry to everyday life — the air we breathe, the water we drink, the fuels we burn and the impact on our environment.
Key concepts
- Composition of air
- About 78% nitrogen, 21% oxygen, small amounts of argon, CO₂ and water vapour.
- Combustion of fuels
- Complete: fuel + O₂ → CO₂ + H₂O; incomplete: also gives CO and/or C (soot).
- Air pollutants
- CO (toxic), SO₂ and NOₓ (acid rain), particulates (respiratory disease), CO₂ (climate change).
- Water treatment
- Filtration removes solids; chlorination kills microbes; distillation gives pure water.
- Acid rain forms when SO₂ and NOₓ dissolve in atmospheric water.
- Greenhouse gases (CO₂, CH₄, H₂O) trap infrared radiation and enhance the greenhouse effect.
- Hydrogen is a clean fuel — burns to give only water — but is expensive to make and store.
- Test for water: turns anhydrous copper sulfate from white to blue. Test for pure water: boils at exactly 100 °C.
Worked example
Explain why incomplete combustion of methane in a faulty boiler is dangerous.
- 1Incomplete combustion produces carbon monoxide (CO) as well as CO₂ and H₂O.
- 2CO is a colourless, odourless, toxic gas.
- 3It binds to haemoglobin more strongly than oxygen, reducing oxygen transport in the blood.
- 4This can cause suffocation and death — hence the need for CO alarms.
Answer: Incomplete combustion makes toxic CO, which stops blood carrying oxygen properly.
Common mistakes
✗ Confusing acid rain gases (SO₂, NOₓ) with greenhouse gases (CO₂, CH₄).
✓ Acid rain is about non-metal oxides dissolving in water; the greenhouse effect is about trapping infrared radiation.
✗ Saying pure water 'is safe to drink'.
✓ Distilled water is chemically pure but tap water is treated (filtered + chlorinated) to be safe to drink.
✗ Ignoring the difference between 'clean' and 'renewable' fuels.
✓ Hydrogen is clean (product is water) but not necessarily renewable; the way it is made determines that.
Quick check
Try these, then reveal the answers.
Which two gases make up the majority of the atmosphere?Reveal answer
Nitrogen (~78%) and oxygen (~21%).
What gas turns limewater cloudy?Reveal answer
Carbon dioxide.
Why is chlorine added to drinking water?Reveal answer
To kill harmful microbes.
Exam tips
- Link cause → pollutant → effect for pollution questions (e.g. cars → NOₓ → acid rain).
- For fuel comparisons, discuss energy released, storage, cost and pollutants — not just one factor.
- Learn both tests for water (chemical test for presence, boiling point for purity).
Related practice
Practise this topic
Exam-style questions with instant Gradion feedback.
Flashcards
Quick-fire recall to lock in the key facts.
Worksheets
Printable practice you can work through offline.
Past papers
Full papers with examiner-grade marking.
Gradion
Ask for a step-by-step explanation any time.
All Chemistry
Every Chemistry topic across every exam board.
Related topics
Frequently asked questions
What causes climate change?+
Increased greenhouse gases (mainly CO₂ from burning fossil fuels) trap more infrared radiation, warming the Earth's surface.
How is drinking water treated?+
Water is filtered to remove solids and then chlorinated to kill microbes; sometimes fluoride and pH adjusters are added.
Create a free account to practise chemistry in society with Gradion feedback
Try 5 questions now, get instant examiner-grade marking and ask the Gradion to explain anything. Free during our early launch period — no credit card required.