Using Resources
Using resources covers how humans obtain and use the Earth's limited natural resources sustainably. It covers the production of potable water from fresh water and, where necessary, by desalination, the treatment of sewage, life cycle assessment as a way to compare the environmental impact of products, the importance of reducing, reusing and recycling limited resources, the corrosion of metals such as iron and how it is prevented, and why most everyday metal objects are alloys rather than pure metals.
Method
- Distinguish finite resources, such as metal ores and crude oil, which are used up faster than natural processes can replace them, from renewable resources, such as timber and biofuel crops, which can be replenished at a usable rate; describe sustainable development as meeting the needs of today's population without compromising the ability of future generations to meet their own needs.
- Describe the production of potable water (water that is safe to drink, which is not the same as chemically pure water) from an available fresh water source such as a river, lake or reservoir: it is passed through filtration to remove solid particles and suspended matter, then sterilised (commonly by adding chlorine, or by using ozone or ultraviolet light) to kill microorganisms.
- Describe desalination, used where there is insufficient fresh water, for example a coastal or arid region: seawater is either distilled (heated so that water evaporates, then the vapour is condensed, leaving the dissolved salts behind) or passed through reverse osmosis (forced through a membrane that lets water molecules through but blocks larger dissolved ions); both methods use large amounts of energy, making desalination more expensive than treating fresh water.
- Outline the stages of sewage treatment: screening removes large solid objects and grit; sedimentation allows sludge to settle out from the remaining liquid (effluent); the effluent is treated aerobically by microorganisms that break down remaining organic matter and pathogens; the separated sludge is treated anaerobically by different microorganisms, and can then be used as a fertiliser or as a source of biogas fuel.
- Use life cycle assessment (LCA) to compare the total environmental impact of two or more products across every stage: extracting and processing the raw materials, manufacturing and packaging the product, using the product, and finally disposing of it, considering the energy, water and other resources used and the waste produced at each stage.
- Apply the principle of reducing, reusing and recycling to limit the use of finite resources: reducing the amount of a resource used, reusing an item rather than discarding it, and recycling materials (which for metals typically needs much less energy than extracting the same metal from its ore) all conserve limited raw materials and reduce landfill waste.
Worked example
A drinks company compares glass bottles and plastic (PET) bottles for the same drink using life cycle assessment. Explain, stage by stage, one advantage each type of bottle might show, and explain why a full life cycle assessment is more reliable than comparing the two bottles on a single measure such as weight.
- Consider the raw material and manufacturing stage: glass is made mainly from abundant raw materials (sand, and recycled glass), but manufacturing it requires melting the raw materials at a very high temperature, which uses a large amount of energy; plastic bottles are made from crude oil, a finite resource, but generally need less energy to manufacture and are much lighter.
- Consider the use stage: the lighter plastic bottle needs less fuel to transport per bottle delivered, since transport energy depends on the mass being moved, which is an advantage for plastic on this stage alone.
- Consider the disposal stage: glass can be recycled repeatedly without loss of quality and is chemically inert if it ends up in landfill, whereas some plastics are harder to recycle economically and, if littered, can persist in the environment or in the oceans for a very long time.
- Explain why comparing on weight alone is unreliable: weight only reflects one stage (transport), and ignores the very different energy costs of manufacture, the different resources consumed (finite crude oil compared with more abundant sand), and the different environmental impacts at disposal.
- Final answer: a full life cycle assessment considers raw materials, manufacture, use and disposal together, so it gives a much more complete and reliable comparison than judging the two bottle types on any single stage or measure alone.
Practice questions
Try each question, then tap to reveal the answer.
Q1Define a finite resource, giving one example.Show answer
Answer: A resource that is being used up faster than it can be replaced by natural processes, for example metal ores or crude oil.
Q2State the two main steps used to produce potable water from a fresh water source.Show answer
Answer: Filtration (to remove solid particles) followed by sterilisation (for example with chlorine, ozone or ultraviolet light, to kill microorganisms).
Q3Name two methods of desalinating seawater.Show answer
Answer: Distillation and reverse osmosis.
Q4Explain why potable water is not the same as pure water.Show answer
Answer: Potable water is safe to drink but still contains low levels of dissolved substances, such as minerals, whereas pure water contains only H2O with nothing else dissolved in it.
Q5Name the four stages usually considered in a life cycle assessment of a product.Show answer
Answer: Extracting and processing the raw materials, manufacturing and packaging, use, and disposal at the end of the product's life.
Q6State one benefit of recycling metal rather than extracting new metal from its ore.Show answer
Answer: Recycling metal generally uses much less energy than mining and extracting a new metal from its ore, and it conserves the limited supply of that metal's ore.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
A region has plenty of seawater but very little fresh water available. Describe how the region could produce potable water, and explain why this is likely to be more expensive than in a region with an abundant fresh water supply.
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Explain how life cycle assessment can be used to compare the overall environmental impact of two competing products, and give one reason why a life cycle assessment produced by the manufacturer of one of the products might not be fully objective.
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Free printable worksheet
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This topic is chapter 5 of GCSE Chemistry Workbook, the whole course as one free printable PDF.
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