Eduqas GCSE Chemistry 12 The Earth and its Atmosphere Exam Questions

About Eduqas GCSE Chemistry 12 The Earth and its Atmosphere

The Earth and its atmosphere is the final topic in Eduqas GCSE Chemistry. It explains how the early atmosphere formed from volcanic activity, how oxygen increased through photosynthesis and how carbon dioxide decreased as it was locked into sedimentary rocks and fossil fuels. You then study the greenhouse effect, human activities that increase greenhouse gases, evidence for climate change and its uncertainties, and carbon footprints. Air pollutants from burning fuels, such as carbon monoxide, sulfur dioxide, oxides of nitrogen and particulates, are also covered, along with producing potable water. It links to combustion in topic 10. Examiners often ask for explanations of the greenhouse effect and evaluations of climate data.

What you need to know

• Composition of air Today's dry air is about 78% nitrogen, 21% oxygen, about 0.9% argon and around 0.04% carbon dioxide, with other gases in small amounts.
• Early atmosphere The early atmosphere is thought to have been mainly carbon dioxide and water vapour from volcanoes, with little oxygen. Water vapour condensed to form oceans; algae and plants photosynthesised, increasing oxygen and removing carbon dioxide, which was also stored in sedimentary rocks and fossil fuels.
• Greenhouse effect Short wavelength radiation from the Sun passes through the atmosphere and is absorbed by the Earth, which emits longer wavelength infrared radiation. Greenhouse gases such as carbon dioxide, methane and water vapour absorb this and re-emit it, warming the atmosphere.
• Climate change Burning fossil fuels, deforestation and livestock farming increase greenhouse gases. Possible effects include rising sea levels, extreme weather and changes to species distribution. Data are complex and models involve uncertainty. A carbon footprint is the total greenhouse gases emitted over the life of a product or activity.
• Air pollutants Incomplete combustion produces carbon monoxide (toxic) and particulates (global dimming, lung damage). Sulfur dioxide and oxides of nitrogen cause acid rain and breathing problems.
• Potable water Potable water is safe to drink. In the UK, fresh water is filtered and sterilised with chlorine, ozone or ultraviolet light. Desalination of sea water by distillation or reverse osmosis needs large amounts of energy.

Common mistakes in 12 The Earth and its Atmosphere

• Saying the greenhouse effect is caused by the hole in the ozone layer. They are different issues; the greenhouse effect involves gases absorbing infrared radiation.
• Writing that greenhouse gases trap heat by reflecting it back. They absorb infrared radiation and re-emit it in all directions, including back towards the Earth.
• Saying potable water is pure water. Potable water is safe to drink but contains dissolved substances.
• Writing that carbon monoxide causes acid rain. Sulfur dioxide and oxides of nitrogen cause acid rain; carbon monoxide is toxic because it reduces the oxygen carried by the blood.
• Saying the early atmosphere contained lots of oxygen. Oxygen built up later, mainly through photosynthesis by algae and plants.

Try three 12 The Earth and its Atmosphere exam-style questions