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Cambridge IGCSE Chemistry · 0620
Chapter 10: Chemistry of the Environment — Part 2
Topic 10.3 · Air quality and climate
Composition of Clean, Dry Air
Clean air is a mixture of gases approximately composed of:
- 78% Nitrogen (N2).
- 21% Oxygen (O2).
- The remainder is a mixture of noble gases and carbon dioxide (CO2).
Air Pollutants: Sources and Adverse Effects
| Pollutant | Source | Adverse Effect |
|---|---|---|
| Carbon dioxide (CO2) | Complete combustion of carbon-containing fuels. | Increased global warming and climate change. |
| Carbon monoxide (CO) | Incomplete combustion of carbon-containing fuels. | Toxic gas. |
| Particulates (Soot) | Incomplete combustion of carbon-containing fuels. | Increased risk of respiratory problems and cancer. |
| Methane (CH4) | Decomposition of vegetation and waste gases from animal digestion. | Increased global warming and climate change. |
| Oxides of Nitrogen (NOx) | Reaction of N2 and O2 in car engines at high pressure/temp. | Acid rain, photochemical smog, and respiratory issues. |
| Sulfur dioxide (SO2) | Combustion of fossil fuels containing sulfur compounds. | Acid rain. |
Exam Traps
- CO is toxic; CO2 is not toxic but contributes to global warming — do not swap their adverse effects.
The Greenhouse Effect
Greenhouse gases like carbon dioxide and methane maintain Earth's temperature by:
- Allowing short-wavelength radiation from the sun to pass through the atmosphere.
- The Earth absorbs this radiation and re-emits it as infrared (IR) radiation.
- Greenhouse gases absorb this IR radiation and re-emit it in all directions, trapping thermal energy within the atmosphere and contributing to global warming.
Strategies to Reduce Environmental Issues
- Climate Change: Planting trees, reducing livestock farming, decreasing fossil fuel use, and increasing use of hydrogen and renewable energy.
- Acid Rain:
- Catalytic Converters: Fitted in cars to remove oxides of nitrogen by catalysing the reaction: 2CO + 2NO ? 2CO2 + N2.
- Low-sulfur fuels: Reducing SO2 at the source.
- Flue gas desulfurisation: Using calcium oxide to remove SO2 from industrial exhaust gases by forming calcium sulfate.
Exam Traps
- Flue gas desulfurisation targets SO2 from power stations — do not confuse it with catalytic converters in cars.
Photosynthesis
Photosynthesis is the process where plants use chlorophyll and sunlight to react carbon dioxide and water to produce glucose and oxygen.
- Word Equation: Carbon dioxide + Water ? Glucose + Oxygen.
- Symbol Equation: 6CO2 + 6H2O ? C6H12O6 + 6O2.
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