GCSE / Chemistry
Using Resources
Study how natural resources are used sustainably, how potable water and waste water are treated, how metals are extracted and recycled, and how materials such as alloys, polymers, ceramics and composites are selected for different uses. This topic also covers corrosion, life cycle assessments, the Haber process and NPK fertilisers.
Natural resources are materials obtained from the Earth, oceans and atmosphere. Some resources are finite and will eventually run out, while renewable resources can be replaced naturally.
Sustainable development means meeting the needs of the present generation without preventing future generations from meeting their own needs. Chemistry can help reduce the use of limited resources, energy consumption, waste and environmental damage.
Potable water is water that is safe to drink. It is not chemically pure because it contains small amounts of dissolved substances, but it must contain sufficiently low levels of dissolved salts and microorganisms.
In the UK, potable water is commonly produced from fresh water by choosing a suitable source, passing the water through filters and sterilising it. Sterilisation can use chlorine, ozone or ultraviolet light.
When fresh water is limited, salty water can be desalinated. Desalination can use distillation or membrane processes such as reverse osmosis, although these methods require significant amounts of energy.
Waste water from homes, agriculture and industry must be treated before being released into the environment. Sewage treatment includes screening and grit removal, sedimentation, anaerobic digestion of sludge and aerobic treatment of the effluent.
Phytomining and bioleaching are alternative methods of extracting metals from low-grade ores. Phytomining uses plants to absorb metal compounds, while bioleaching uses bacteria to produce solutions containing metal compounds.
A life cycle assessment evaluates the environmental impact of a product during extraction and processing of raw materials, manufacturing and packaging, use during its lifetime, and disposal at the end of its useful life.
Reducing, reusing and recycling materials lowers the demand for finite resources, reduces energy use and decreases waste. Metals, glass and some other materials can often be recycled into new products.
Corrosion is the destruction of materials by chemical reactions with substances in the environment. Rusting of iron requires both oxygen and water.
Corrosion can be prevented using barrier methods such as painting, greasing and electroplating. Sacrificial protection uses a more reactive metal, such as zinc, to protect iron from corrosion.
Most metals used in everyday products are alloys. Bronze is mainly copper and tin, brass is mainly copper and zinc, and steels are alloys of iron containing carbon and sometimes other elements.
Different alloys have different properties. High-carbon steel is strong but brittle, low-carbon steel is softer and easier to shape, stainless steel contains chromium and nickel and is resistant to corrosion, and aluminium alloys have low density.
Ceramics, polymers and composites are important engineered materials. Thermosoftening polymers soften or melt when heated, while thermosetting polymers do not melt because of their cross-linked structures. Composites combine a matrix or binder with a reinforcement.
The Haber process produces ammonia from nitrogen and hydrogen using an iron catalyst, high temperature and high pressure. The reaction is reversible, and unreacted gases are recycled. Ammonia is used to make nitrogen fertilisers, including ammonium salts and NPK fertilisers containing nitrogen, phosphorus and potassium.