Air, Water and the Environment: notes

Air

• Composition of air: about 78 percent nitrogen, 21 percent oxygen, 0.04 percent carbon dioxide and small amounts of argon and other gases.
• Oxygen: needed for burning and breathing. Magnesium + oxygen gives magnesium oxide, which shows that oxygen is used up when metals burn.
• Nitrogen: an unreactive gas that makes up most of the air. Plants take in nitrogen compounds from the soil to grow.
• Air pollution: harmful gases or particles in the air. Smoke from a coal power station is one example.
• Acid rain: rain made acidic by sulphur dioxide and nitrogen oxides. It damages buildings and kills fish in lakes.
• Greenhouse effect: gases such as carbon dioxide trap heat near the Earth. Without this effect the Earth would be too cold for life.
• Global warming: a rise in average temperature caused by extra carbon dioxide from burning fossil fuels. Cutting down forests makes it worse.

Water

• Water treatment: removing solids and germs so water is safe to drink. Water is filtered, then chlorine is added to kill bacteria.
• Test for water: anhydrous copper(II) sulphate paper turns from white to blue when water is present.
• Hard water: water containing calcium or magnesium ions. It forms scum with soap. Boiling it or adding washing soda makes it soft.
• Soft water: water that lathers easily with soap. Rain water is usually soft.
• Eutrophication: fertilisers wash into rivers and lakes, algae grow fast and use up oxygen, so fish die.

The Carbon Cycle

• Carbon cycle: carbon moves between air, plants, animals and soil. Plants take in carbon dioxide for photosynthesis, animals eat plants and breathe out carbon dioxide, and decay returns carbon to the soil.