LEARNING OBJECTIVES
By the end of this chapter, you should be able to:
- test for water and assess purity
- describe water pollutants and treatment
- explain fertiliser use
- identify air pollutants, sources and effects
- explain greenhouse warming
- describe strategies that reduce environmental damage
THE BIG IDEA
Understand water quality, fertilisers, air pollution, climate change and chemical strategies for reducing harm.
Chemistry helps identify pollutants, explain their effects and design methods to reduce them. Environmental decisions often involve trade-offs between energy, food production, cost and risk.
Pure water and safe drinking water are not identical ideas: drinking water contains controlled dissolved substances but must be free from harmful levels of pollutants and microbes.
SECTION 01
Water tests, purity and treatment
Water turns anhydrous cobalt(II) chloride from blue to pink and anhydrous copper(II) sulfate from white to blue. These tests show presence, not purity.
Pure water has sharp melting and boiling points. Distilled water is used in experiments because it contains fewer dissolved impurities than tap water.
Domestic water treatment uses sedimentation and filtration to remove solids, activated carbon to remove tastes and odours, and chlorination to kill microbes.
SECTION 02
Water quality and fertilisers
Natural water may contain useful dissolved oxygen and mineral compounds, but also toxic metals, plastics, sewage microbes, nitrates and phosphates.
Excess nitrates and phosphates can deoxygenate water and harm aquatic life. Sewage can spread disease.
Ammonium salts and nitrates supply nitrogen. NPK fertilisers provide nitrogen, phosphorus and potassium to improve plant growth.
KEY IDEAS
- Dissolved oxygen supports aquatic respiration.
- Fertiliser benefits must be balanced against runoff and water damage.
SECTION 03
Air pollutants and their effects
Clean dry air is about 78% nitrogen, 21% oxygen, with noble gases and carbon dioxide making up most of the remainder.
Complete combustion produces carbon dioxide. Incomplete combustion produces toxic carbon monoxide and particulates, which increase respiratory disease and cancer risk.
Methane comes from decomposition and animal digestion. Hot engines form nitrogen oxides; sulfur-containing fuels produce sulfur dioxide. Nitrogen oxides cause smog, acid rain and respiratory problems; sulfur dioxide causes acid rain.
KEY IDEAS
- Carbon dioxide and methane increase global warming.
- Pollutant source, chemical identity and effect should be stated separately.
SECTION 04
Climate and pollution control
Greenhouse gases absorb, emit and redirect outgoing thermal energy, reducing energy loss to space and raising average global temperature.
Climate strategies include planting trees, reducing fossil-fuel use and livestock farming, and increasing renewable energy or low-carbon hydrogen.
Catalytic converters remove carbon monoxide and nitrogen monoxide. Low-sulfur fuels and flue-gas desulfurisation with calcium oxide reduce sulfur dioxide.
Photosynthesis transfers carbon dioxide and water into glucose and oxygen using light energy and chlorophyll.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Water tests identify presence; melting and boiling points assess purity.
- Treatment removes solids, tastes, odours and microbes.
- Fertilisers support growth but runoff can damage water.
- Pollutants have distinct sources and effects.
- Greenhouse gases reduce thermal-energy loss to space.