IGCSE Chemistry 0620 · Topic 10: Chemistry of the Environment
Chemistry of the Environment
This topic connects chemistry to real-world issues: what’s in the air we breathe, where pollutants come from, and how human activity is changing the climate.
1. Composition of Clean, Dry Air
Approximately 78% nitrogen, 21% oxygen, 0.04% carbon dioxide, with the remainder mostly noble gases (chiefly argon).
2. Air Pollutants
Pollutant
Source
Effect
Carbon monoxide
Incomplete combustion of fuels
Toxic — binds to haemoglobin, reducing oxygen transport
Sulfur dioxide
Burning fossil fuels containing sulfur
Causes acid rain, respiratory problems
Oxides of nitrogen (NOₓ)
Car engines (high temperature combustion)
Causes acid rain, respiratory problems
Particulates
Incomplete combustion
Respiratory problems, global dimming
Acid rain formation
Sulfur dioxide and nitrogen oxides dissolve in atmospheric water and react with oxygen, forming dilute sulfuric acid and nitric acid, which fall as acid rain: SO₂ + H₂O + ½O₂ → H₂SO₄ (simplified). Acid rain damages plants, kills aquatic life, and erodes limestone buildings and statues.
3. Greenhouse Effect and Climate Change
Greenhouse gases (mainly carbon dioxide and methane) absorb infrared radiation re-emitted from the Earth’s surface, trapping heat in the atmosphere. Rising levels from burning fossil fuels and deforestation are linked to global warming and climate change.
Catalytic converters
Fitted to car exhausts, catalytic converters use a catalyst (platinum/palladium/rhodium) to convert toxic gases into less harmful ones, e.g. 2CO + 2NO → 2CO₂ + N₂
Photosynthesis and the carbon cycle
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (using light energy). Photosynthesis removes CO₂ from the air, balancing (in principle) the CO₂ released by respiration and combustion — this balance is disrupted by deforestation and burning fossil fuels.
Common mistakes to watch for
Confusing acid rain (caused by SO₂/NOₓ) with the greenhouse effect (caused by CO₂/methane) — they are different problems with different causes.
Forgetting fertiliser overuse causes eutrophication: excess nutrients run into waterways, causing algal blooms that block light and deplete oxygen as they decompose, killing aquatic life.
Describing carbon monoxide as smelly or visible — it is actually colourless and odourless, which is part of why it’s so dangerous.
Key Vocabulary Recap
Eutrophication — excess nutrients causing algal blooms and oxygen depletion in water
Greenhouse gas — a gas that traps infrared radiation, warming the atmosphere
Syllabus Reference
This note covers IGCSE Chemistry 0620 Topic 10, Chemistry of the Environment: water and water treatment, fertilisers, composition of air, air pollutants, climate change, acid rain, greenhouse gases, catalytic converters, and photosynthesis.
Practice questions
IGCSE Chemistry 0620 · Topic 10: Chemistry of the Environment — Practice Question Bank (no answers)
Chemistry of the Environment — Practice
Covers: air composition, pollutants, acid rain, greenhouse effect, and photosynthesis. 10 questions.
Q1 Core
State the approximate percentages of nitrogen, oxygen, and carbon dioxide in clean, dry air.
Q2 Core
State the source and one effect of sulfur dioxide as an air pollutant.
Q3 Core
Explain why carbon monoxide is dangerous to human health.
Q4 Core
Explain how acid rain forms, and state two of its harmful effects.
Q5 Core
Explain how the greenhouse effect causes global warming.
Q6 Core
Name two greenhouse gases and state one human activity that increases their levels.
Q7 Extended
Describe how a catalytic converter reduces pollution from a car exhaust, giving an example equation.
Q8 Core
Write the balanced equation for photosynthesis.
Q9 Extended
Explain the process of eutrophication caused by excess fertiliser use.
Q10 Core
Describe two methods used in the treatment of water to make it safe to drink.
Worked solutions
Show worked solutions
IGCSE Chemistry 0620 · Topic 10: Chemistry of the Environment — Solutions
Chemistry of the Environment — Practice: Solutions
Q1
Composition of clean, dry air.
✓Approximately 78% nitrogen, 21% oxygen, and 0.04% carbon dioxide (with the remainder mostly noble gases, chiefly argon).
Q2
Source and effect of SO₂.
✓Source: burning fossil fuels that contain sulfur impurities. Effect: causes acid rain (and contributes to respiratory problems).
Q3
Why is CO dangerous?
✓Carbon monoxide binds to haemoglobin in red blood cells more strongly than oxygen does, reducing the blood’s ability to carry oxygen around the body — this can lead to oxygen starvation and death, and it is especially dangerous because it is colourless and odourless.
Q4
How does acid rain form; two effects.
✓Sulfur dioxide and nitrogen oxides released into the atmosphere dissolve in rainwater and react with oxygen, forming dilute sulfuric acid and nitric acid. Effects: damages/kills plants and aquatic life; erodes limestone buildings and statues.
Q5
How does the greenhouse effect cause warming?
✓Greenhouse gases in the atmosphere absorb infrared radiation that is re-emitted from the Earth’s surface (after it has been warmed by sunlight), trapping this energy in the atmosphere rather than letting it escape into space — this raises the average global temperature.
Q6
Two greenhouse gases and a human cause.
✓Carbon dioxide and methane. CO₂ levels increase due to burning fossil fuels and deforestation; methane levels increase due to livestock farming and landfill waste.
Q7
How does a catalytic converter work?
✓A catalytic converter contains a catalyst (e.g. platinum) that speeds up reactions converting toxic exhaust gases into less harmful ones as they pass through, without being used up itself. Example: 2CO + 2NO → 2CO₂ + N₂
Q8
Photosynthesis equation.
✓6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (using light energy)
Q9
Explain eutrophication.
✓Excess fertiliser runs off farmland into rivers and lakes, providing excess nutrients that cause algae to grow rapidly (an algal bloom), blocking light from reaching plants below the surface. When the algae and plants die, decomposing microorganisms use up the dissolved oxygen in the water, killing fish and other aquatic life.
Q10
Two water treatment methods.
✓Any two of: filtration (to remove solid particles/sediment), sedimentation, and chlorination (to kill microorganisms and make the water safe to drink).
