Chemistry of the Environment

The One Thing

Environmental chemistry explains how chemical substances affect water, air, climate, and ecosystems, and how treatment, pollution control, efficient resource use, and sustainable practices can reduce these effects. Environmental decisions require balancing human needs with impacts on health, ecosystems, climate, resources, cost, energy use, and waste.

Reactions, Processes and Experiments

Key Terms

• Potable water: Water that is safe to drink because it contains no harmful levels of dissolved substances or microorganisms.
• Water treatment: The sequence of processes used to make water suitable for drinking, usually including filtration and sterilisation.
• Filtration: Separating insoluble solid particles from water by passing it through a porous material such as sand.
• Sterilisation: Killing microorganisms in water using chlorine, ozone, or ultraviolet radiation.
• Distillation: Purifying water by boiling it and condensing the vapour, leaving many dissolved substances behind.
• Atmosphere: The mixture of gases surrounding Earth.
• Air pollutant: A substance released into the atmosphere at a concentration that can harm living organisms, materials, or the environment.
• Complete combustion: Burning a fuel in excess oxygen to produce carbon dioxide and water.
• Incomplete combustion: Burning a fuel with insufficient oxygen, producing carbon monoxide and sometimes carbon particles as well as water.
• Carbon monoxide: A poisonous gas formed by incomplete combustion; it reduces the blood’s ability to transport oxygen.
• Sulfur dioxide: A pollutant formed mainly when sulfur-containing fuels burn; it can cause respiratory problems and acid rain.
• Nitrogen oxides: Gases such as nitrogen monoxide and nitrogen dioxide formed at high temperatures in engines; they contribute to acid rain and photochemical smog.
• Particulates: Tiny solid particles or liquid droplets suspended in air, often produced by combustion, that can damage the respiratory system.
• Greenhouse gas: A gas that absorbs outgoing infrared radiation and helps warm Earth’s atmosphere.
• Greenhouse effect: The natural warming of Earth caused when greenhouse gases absorb and re-emit infrared radiation.
• Enhanced greenhouse effect: Additional warming caused by increased concentrations of greenhouse gases from human activities.
• Carbon dioxide: A greenhouse gas released by fossil-fuel combustion, deforestation, and cement production; it is also removed by photosynthesis and absorption by oceans.
• Methane: A greenhouse gas released by livestock, landfill, rice cultivation, and leaks from fossil-fuel extraction; it is more effective per molecule than carbon dioxide at absorbing infrared radiation.
• Acid rain: Rain made more acidic when sulfur dioxide and nitrogen oxides react with oxygen and water in the atmosphere.
• Photochemical smog: A mixture of pollutants formed when nitrogen oxides and hydrocarbons react in sunlight, producing substances including ozone.
• Ozone layer: A region of the stratosphere containing relatively high ozone concentration that absorbs harmful ultraviolet radiation.
• Ozone depletion: The reduction of stratospheric ozone caused mainly by chlorine and bromine radicals released from compounds such as chlorofluorocarbons.
• Catalytic converter: A device in vehicle exhaust systems that converts carbon monoxide and nitrogen oxides into less harmful substances.
• Carbon cycle: The movement of carbon between the atmosphere, living organisms, oceans, soils, and rocks through processes such as photosynthesis, respiration, combustion, and decay.
• Sustainability: Using resources in a way that meets present needs without preventing future generations from meeting theirs.

Easily Confused

• Complete combustion and incomplete combustion: Complete combustion uses excess oxygen and produces carbon dioxide and water; incomplete combustion uses insufficient oxygen and may produce carbon monoxide or carbon particles.
• Stratospheric ozone and ground-level ozone: Stratospheric ozone absorbs harmful ultraviolet radiation and is protective; ground-level ozone is a pollutant that can irritate lungs and damage plants.
• Greenhouse effect and enhanced greenhouse effect: The greenhouse effect is natural and necessary for life; the enhanced greenhouse effect results from increased greenhouse-gas concentrations caused by human activities.
• Filtration and distillation: Filtration removes insoluble solid particles; distillation involves boiling and condensing water to leave many dissolved substances behind.
• Sterilisation and filtration: Sterilisation kills microorganisms; filtration separates insoluble solid particles.
• Carbon dioxide and methane: Both are greenhouse gases, but methane is more effective per molecule at absorbing infrared radiation.
• Acid rain and photochemical smog: Acid rain is associated with sulfur dioxide and nitrogen oxides reacting with oxygen and water; photochemical smog forms when nitrogen oxides and hydrocarbons react in sunlight.
• Ozone depletion and photochemical smog: Ozone depletion reduces protective stratospheric ozone through chlorine and bromine radicals; photochemical smog produces harmful ozone near ground level.
• Carbon monoxide and carbon dioxide: Carbon monoxide is poisonous and formed by incomplete combustion; carbon dioxide is a greenhouse gas formed by complete combustion and several other processes.
• Water treatment and distillation: Water treatment commonly involves screening, sedimentation, filtration, and sterilisation; distillation is a separate purification method requiring considerable energy.

What Gets Asked

• Describe a drinking-water treatment sequence: State screening, sedimentation, filtration, and sterilisation, and explain that filtration removes insoluble particles while sterilisation kills microorganisms. A common error is treating filtration as a method for killing microorganisms.
• Write or balance a combustion equation: Use hydrocarbon + oxygen → carbon dioxide + water for complete combustion and distinguish it from equations producing carbon monoxide or carbon. A common mark-losing error is assigning carbon monoxide to complete combustion.
• Explain acid rain formation: Include sulfur dioxide oxidation, SO2 + O2 → SO3, followed by SO3 + H2O → H2SO4, and refer to nitrogen oxides forming nitric acid. Omitting the atmospheric reactions loses the chemical explanation.
• Explain catalytic converters: Use 2CO + 2NO → 2CO2 + N2 and identify the conversion of carbon monoxide and nitrogen oxides into less harmful substances. Do not describe the converter as removing all exhaust pollutants.
• Compare the greenhouse effect with the enhanced greenhouse effect: Explain that the natural greenhouse effect is necessary for life, whereas increased greenhouse-gas concentrations from human activities cause additional warming. A frequent error is describing the natural greenhouse effect itself as entirely harmful.
• Explain ozone depletion or photochemical smog: For ozone depletion, include chlorofluorocarbons, ultraviolet radiation, chlorine radicals, and the reactions Cl· + O3 → ClO· + O2 and ClO· + O → Cl· + O2. For photochemical smog, include nitrogen oxides, hydrocarbons, sunlight, and ozone. A common error is confusing protective stratospheric ozone with harmful ground-level ozone.