2 - My Home
House design involves many types of science. Construction workers use their knowledge and understanding of materials to build homes that are strong and secure. Energy consultants design energy saving features to keep us warm in winter. Chemists, using their knowledge of chemical energy, have helped to develop a range of fuels for cooking, heating and transport, and using their knowledge of materials have created a wide variety of products found in the home. Energy company employees ensure that the electricity generated by our power stations is distributed all over the country to our homes.
2.1 Materials used to construct our homes
Candidates need to understand that:
Limestone can be changed chemically to make a variety of construction materials. It can be used to make quicklime and slaked lime. Limestone also provides a starting point for the manufacture of cement, concrete and glass.
Metals have several different uses in construction according to their properties and patterns in reactivity.
Polymers, ceramics and composites are examples of manufactured construction materials. Wood is an example of a natural construction material.
Understanding the structure, properties and chemical reactions of these materials enables the building industry to pick the most suitable material for a particular use.
Architects and construction companies are now considering more sustainable methods of house construction.
Candidates need to:
1. Know that limestone is obtained from the ground by quarrying.
2. Give some uses of limestone in the building industry.
3. Describe the conversion of limestone into quicklime and quicklime into slaked lime, and know the chemical formulae for these materials.
4. Outline the manufacturing processes for the production of quicklime, cement and glass.
5. Describe the composition and use of mortar and concrete.
6. Know the characteristic properties of metals (good heat and electrical conductors, malleability, ductility, resistance to corrosion, strength and hardness). Knowledge of the structure of and bonding in metals, and the effects of alloying on the properties of a metal, is not required.
7. Relate uses of metals in the building industry to the properties of these metals. Copper is used for water pipes and hot water cylinders because it is malleable, strong, has a high melting point, is a good conductor of electricity and does not react with water. Copper is used for wiring because it is strong, ductile, has a high melting point and is a good conductor of electricity. Lead is used for flashing on roofs because it is unreactive and malleable. Steel is used to make supporting structures and fixings because it has a high tensile strength. Aluminium is used in window frames because it is resistant to corrosion, malleable, strong and light.
8. Know that most polymers are manufactured using chemicals obtained from crude oil.
9. Describe how polymers are produced when many small molecules (monomers) join together to form very large molecules (polymerisation). Details of polymerisation required are limited to representation of the formation of poly(ethene) from ethene. The effects of cross-linking, altering chain length and branching chains on the properties of polymers are not required.
10. Know that polymers are flexible, poor conductors of heat and electricity, resistant to corrosion, waterproof and that most of them have low melting points. These properties relate to their uses in the home. Polymers used in construction are poly(ethene), poly(propene), polystyrene and PVC. Most polymers have low melting points, which makes them easy to mould into shapes. They are used for electrical and thermal insulation (because they are poor conductors of heat and electricity), pipes and guttering, containers for water and other chemicals.
11. Relate the characteristic properties of ceramics (for example, brittle, high melting point) to their uses in construction. Ceramics are hard, brittle solids with high melting points and are resistant to chemical attack. They are used for construction and decoration (bricks and tiles), pottery products (bathroom basins and toilets) and specialist industrial materials (for example, lining for furnaces and insulators on power transmission lines).
12. Be able to recognise and describe a composite material (for example, MDF, fibreglass, reinforced concrete).
13. Describe the properties of a composite as a combination of the properties of its components.
Within this context, candidates should be able to use scientific data and evidence to discuss, evaluate or suggest implications of the following:
■ the use of quarrying to obtain raw materials for building
■ the physical properties of materials
■ the most suitable material for a particular use
■ the developments in modern (sustainable) building materials, and their advantages and disadvantages when compared with more traditional materials including straw bale, wood frame and cob construction
■ changes in the properties of materials resulting from a change of structure.
2.2 Fuels for cooking, heating and transport
Candidates need to understand that:
The chemical energy in hydrocarbons is released when they are burned in air, which makes them useful as fuels.
Crude oil is an important source for a range of other fuels used for cooking and heating in our homes and for transport. Environmental scientists are concerned about the use of fuels obtained from crude oil for cooking, heating and transport.
Candidates need to:
1. Name suitable fuels for cooking, heating our homes and for providing transport. Suitable fuels include natural gas, petrol, diesel, kerosene (paraffin) and heating oil.
2. Know that hydrocarbons contain carbon and hydrogen only.
3. Explain some of the problems of burning fossil fuels (pollution, carbon dioxide production and global warming) and that resources of fossil fuels are finite.
4. Write word and symbol equations for the combustion of hydrocarbons.
5. HT only: write balanced symbol equations for the complete combustion of hydrocarbons.
6. Explain the patterns in the combustion of hydrocarbon fuels. Candidates should recognise the pattern in chemical formulae based on CnH2n + 2. They should be able to recognise qualitative and quantitative patterns in the amounts of reactants and products.
Within this context, candidates should be able to use scientific data and evidence to discuss, evaluate or suggest implications of the following:
■ the social, economic and environmental impacts of the uses of fuels obtained from crude oil for cooking, heating and transport
■ the energy content of different fuels.
2.3 Generation and distribution of electricity
Candidates need to understand that:
There is a range of ways of generating electricity to power our homes and there are many advantages and disadvantages of using different methods. In most power stations electricity is generated by using a fuel to boil water, and then using the steam produced to turn a turbine, which rotates a generator to generate electricity.
Many people are becoming more concerned about the environmental problems and possible health risks of distributing electricity over the land by pylons and high-voltage cables.
Candidates need to:
1. Define the terms renewable and non-renewable in the context of energy sources.
2. Know that fossil fuels (natural gas, oil and coal) release energy when they are burned, which can be used to generate electricity for our homes.
3. Explain how nuclear fuels and renewable energy sources (wind, solar, hydroelectric, wave, tidal, biomass and geothermal) may be used as alternatives to fossil fuels.
4. Know that nuclear fuels produce energy from nuclear fission. Details of nuclear fission or fusion are not required.
5. Explain the problems of using nuclear fuels (problems of radioactive emissions, disposal of waste) and of using renewable energy sources (unreliability and possible effects on the environment). Candidates need to appreciate that nuclear fuels do not produce gases that cause global warming, but that the waste materials produced by them are radioactive. Radioactive emissions are harmful to life so the waste from nuclear power stations has to be stored in a safe place until the radiation falls to safe levels.
6. Describe how electricity can be generated from fossil and nuclear fuels. Details of the construction of generators are not required.
7. Describe how electricity is distributed through the National Grid via high-voltage cables. Candidates should appreciate the use of ‘step up’ and ‘step down’ transformers. A knowledge of transformer construction is not required. Calculations involving transformers are not expected.
Within this context, candidates should be able to use scientific data and evidence to discuss, evaluate or suggest implications of the following:
■ the environmental impact over time of energy production by comparing the advantages and disadvantages of using alternative energy sources
■ the economic impact of using alternative energy sources
■ environmental and health concerns arising from the distribution of electricity by pylons and high-voltage cables.
Suggestions for practical work that could be used to support Theme 2
It is the responsibility of the centre to be aware of the health and safety implications of any practical work, and to ensure that risk assessments for practicals are carried out.
■ Model the limestone cycle: decomposition of CaCO3 to give CaO, reaction with water to give Ca(OH)2, add more water and then filter to give limewater and use of limewater to test for CO2.
■ Thermal decomposition of CaCO3 to show limelight.
■ Make concrete blocks in moulds, varying content, and carry out strength tests.
■ Test physical properties of metals, for example, density/thermal and electrical conductivity.
■ Demonstrate fractional distillation of crude oil using CLEAPSS mixture (take care to avoid confusion with the continuous process in a fractionating column).
■ Test oil fractions for viscosity, ease of ignition and sootiness of flame.
■ Compare the energy content of different fuels, for example, by heating a fixed volume of water.
■ Make models of polymer chains from plastic and cocktail sticks.
■ Test the products of combustion of fuels to show that carbon dioxide is produced.
■ Investigate the effect of changing different variables on the output of solar cells (for example, distance from the light source, the use of different coloured filters and the area of the solar cells).
■ Demonstrate a model water turbine linked to a generator.
■ Model the National Grid.
■ Investigate the properties of ceramics.
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