Chemistry and the Environment
Core concepts
This domain links chemical behaviour to environmental issues. Candidates must understand acids and bases (pH, neutralisation, strong versus weak), oxidation and reduction, and how these explain corrosion, combustion, and photochemical smog. Know the chemistry of carbon dioxide, carbon monoxide, sulfur dioxide, and nitrogen oxides, including their sources and environmental effects: CO₂ as a greenhouse gas, SO₂ and NOₓ as precursors of acid deposition, and NOₓ plus sunlight producing ground-level ozone. Understand solubility and concentration (mol/L, ppm) for measuring pollutants, and bioaccumulation and biomagnification of fat-soluble substances such as some pesticides and methylmercury. Know the difference between biodegradable and persistent pollutants and outline remediation approaches, including neutralising acidic water with lime and reducing emissions through catalytic converters.
Traps to watch
- Confusing the greenhouse effect (normal warming) with enhanced greenhouse effect (human-driven increase).
- Assuming ozone is always beneficial; stratospheric ozone protects, ground-level ozone is a pollutant.
- Reversing oxidation (loss of electrons) and reduction (gain of electrons).
- Forgetting that acid deposition forms when SO₂ and NOₓ react with water in the atmosphere, not from CO₂ alone.
- Treating ppm as a mass unit rather than a concentration ratio.
Worked example
A sample of rainwater has [H⁺] = 1 × 10⁻⁴ mol/L. pH = −log(1 × 10⁻⁴) = 4.0, so the rain is acidic (normal clean rain is about pH 5.6). Rule of thumb: a tenfold change in [H⁺] shifts pH by one unit, and lower pH means higher acidity.