GCSE Chemistry₈₄₆₂

Humans use the Earth’s resources to provide warmth, shelter, food and transport.

Natural resources, supplemented by agriculture, provide food, timber, clothing and fuels.

Finite resources from the Earth, oceans and atmosphere are processed to provide energy and materials.

Chemistry plays an important role in improving agricultural and industrial processes to provide new products and in sustainable development, which is development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.

Students should be able to:

• state examples of natural products that are supplemented or replaced by agricultural and synthetic products
• distinguish between finite and renewable resources given appropriate information.

Students should be able to:

• extract and interpret information about resources from charts, graphs and tables

WS 3.2

MS 2c, 4a

• use orders of magnitude to evaluate the significance of data.

MS 2h

Translate information between graphical and numeric form.

Water of appropriate quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. Water that is safe to drink is called potable water. Potable water is not pure water in the chemical sense because it contains dissolved substances.

The methods used to produce potable water depend on available supplies of water and local conditions.

In the United Kingdom (UK), rain provides water with low levels of dissolved substances (fresh water) that collects in the ground and in lakes and rivers, and most potable water is produced by:

• choosing an appropriate source of fresh water
• passing the water through filter beds
• sterilising.

Sterilising agents used for potable water include chlorine, ozone or ultraviolet light.

If supplies of fresh water are limited, desalination of salty water or sea water may be required. Desalination can be done by distillation or by processes that use membranes such as reverse osmosis. These processes require large amounts of energy.

Students should be able to:

• distinguish between potable water and pure water
• describe the differences in treatment of ground water and salty water
• give reasons for the steps used to produce potable water.

Urban lifestyles and industrial processes produce large amounts of waste water that require treatment before being released into the environment. Sewage and agricultural waste water require removal of organic matter and harmful microbes. Industrial waste water may require removal of organic matter and harmful chemicals.

Sewage treatment includes:

• screening and grit removal
• sedimentation to produce sewage sludge and effluent
• anaerobic digestion of sewage sludge
• aerobic biological treatment of effluent.

Students should be able to comment on the relative ease of obtaining potable water from waste, ground and salt water.

The Earth’s resources of metal ores are limited.

Copper ores are becoming scarce and new ways of extracting copper from low-grade ores include phytomining, and bioleaching. These methods avoid traditional mining methods of digging, moving and disposing of large amounts of rock.

Phytomining uses plants to absorb metal compounds. The plants are harvested and then burned to produce ash that contains metal compounds.

Bioleaching uses bacteria to produce leachate solutions that contain metal compounds.

The metal compounds can be processed to obtain the metal. For example, copper can be obtained from solutions of copper compounds by displacement using scrap iron or by electrolysis.

Students should be able to evaluate alternative biological methods of metal extraction, given appropriate information.

Life cycle assessments (LCAs) are carried out to assess the environmental impact of products in each of these stages:

• extracting and processing raw materials
• manufacturing and packaging
• use and operation during its lifetime
• disposal at the end of its useful life, including transport and distribution at each stage.

Use of water, resources, energy sources and production of some wastes can be fairly easily quantified. Allocating numerical values to pollutant effects is less straightforward and requires value judgements, so LCA is not a purely objective process.

Selective or abbreviated LCAs can be devised to evaluate a product but these can be misused to reach pre-determined conclusions, eg in support of claims for advertising purposes.

Students should be able to carry out simple comparative LCAs for shopping bags made from plastic and paper.

WS 1.3, 4, 5

LCAs should be done as a comparison of the impact on the environment of the stages in the life of a product, and only quantified where data is readily available for energy, water, resources and wastes.

Interpret LCAs of materials or products given appropriate information.

MS 1a

Recognise and use expressions in decimal form.

MS 1c

Use ratios, fractions and percentages.

MS 1d

Make estimates of the results of simple calculations.

MS 2a

Use an appropriate number of significant figures.

MS 4a

Translate information between graphical and numeric form.

The reduction in use, reuse and recycling of materials by end users reduces the use of limited resources, use of energy sources, waste and environmental impacts.

Metals, glass, building materials, clay ceramics and most plastics are produced from limited raw materials. Much of the energy for the processes comes from limited resources. Obtaining raw materials from the Earth by quarrying and mining causes environmental impacts.

Some products, such as glass bottles, can be reused. Glass bottles can be crushed and melted to make different glass products. Other products cannot be reused and so are recycled for a different use.

Metals can be recycled by melting and recasting or reforming into different products. The amount of separation required for recycling depends on the material and the properties required of the final product. For example, some scrap steel can be added to iron from a blast furnace to reduce the amount of iron that needs to be extracted from iron ore.

Students should be able to evaluate ways of reducing the use of limited resources, given appropriate information.

Corrosion is the destruction of materials by chemical reactions with substances in the environment. Rusting is an example of corrosion. Both air and water are necessary for iron to rust.

Corrosion can be prevented by applying a coating that acts as a barrier, such as greasing, painting or electroplating. Aluminium has an oxide coating that protects the metal from further corrosion.

Some coatings are reactive and contain a more reactive metal to provide sacrificial protection, eg zinc is used to galvanise iron.

Students should be able to:

• describe experiments and interpret results to show that both air and water are necessary for rusting
• explain sacrificial protection in terms of relative reactivity.

WS 2.2, 7, 3.5

Investigate the conditions for rusting.

Most metals in everyday use are alloys.

Bronze is an alloy of copper and tin. Brass is an alloy of copper and zinc.

Gold used as jewellery is usually an alloy with silver, copper and zinc. The proportion of gold in the alloy is measured in carats. 24 carat being 100% (pure gold), and 18 carat being 75% gold.

Steels are alloys of iron that contain specific amounts of carbon and other metals. High carbon steel is strong but brittle. Low carbon steel is softer and more easily shaped. Steels containing chromium and nickel (stainless steels) are hard and resistant to corrosion.

Aluminium alloys are low density.

Students should be able to:

• recall a use of each of the alloys specified
• interpret and evaluate the composition and uses of alloys other than those specified given appropriate information.

MS 1a

Recognise and use expressions in decimal form.

MS 1c

Use ratios, fractions and percentages.

Most of the glass we use is soda-lime glass, made by heating a mixture of sand, sodium carbonate and limestone. Borosilicate glass, made from sand and boron trioxide, melts at higher temperatures than soda-lime glass.

Clay ceramics, including pottery and bricks, are made by shaping wet clay and then heating in a furnace.

The properties of polymers depend on what monomers they are made from and the conditions under which they are made. For example, low density (LD) and high density (HD) poly(ethene) are produced from ethene.

Thermosoftening polymers melt when they are heated. Thermosetting polymers do not melt when they are heated.

Students should be able to:

• explain how low density and high density poly(ethene) are both produced from ethene
• explain the difference between thermosoftening and thermosetting polymers in terms of their structures.

Most composites are made of two materials, a matrix or binder surrounding and binding together fibres or fragments of the other material, which is called the reinforcement.

Students should be able to recall some examples of composites.

Students should be able to, given appropriate information:

• compare quantitatively the physical properties of glass and clay ceramics, polymers, composites and metals
• explain how the properties of materials are related to their uses and select appropriate materials.

WS 1.4, 3.5, 3.8

Compare the properties of thermosetting and thermosoftening polymers.

The Haber process is used to manufacture ammonia, which can be used to produce nitrogen-based fertilisers.

The raw materials for the Haber process are nitrogen and hydrogen.

Students should be able to recall a source for the nitrogen and a source for the hydrogen used in the Haber process.

The purified gases are passed over a catalyst of iron at a high temperature (about 450°C) and a high pressure (about 200 atmospheres). Some of the hydrogen and nitrogen reacts to form ammonia. The reaction is reversible so some of the ammonia produced breaks down into nitrogen and hydrogen:

$\mathit{n}\mathit{i}\mathit{t}\mathit{r}\mathit{o}\mathit{g}\mathit{e}\mathit{n}\mathit{ }\mathsf{+}\mathit{h}\mathit{y}\mathit{d}\mathit{r}\mathit{o}\mathit{g}\mathit{e}\mathit{n}\mathit{ }\mathsf{\rightleftharpoons }\mathit{a}\mathit{m}\mathit{m}\mathit{o}\mathit{n}\mathit{i}\mathit{a}$

On cooling, the ammonia liquefies and is removed. The remaining hydrogen and nitrogen are recycled.

MS 1a

Recognise and use expressions in decimal form.

MS 1c

Use ratios, fractions and percentages.

(HT only) Students should be able to:

• interpret graphs of reaction conditions versus rate

MS 1a

Recognise and use expressions in decimal form.

MS 1c

Use ratios, fractions and percentages.

• apply the principles of dynamic equilibrium in Reversible reactions and dynamic equilibrium to the Haber process
• explain the trade-off between rate of production and position of equilibrium
• explain how the commercially used conditions for the Haber process are related to the availability and cost of raw materials and energy supplies, control of equilibrium position and rate.

Compounds of nitrogen, phosphorus and potassium are used as fertilisers to improve agricultural productivity. NPK fertilisers contain compounds of all three elements.

Industrial production of NPK fertilisers can be achieved using a variety of raw materials in several integrated processes. NPK fertilisers are formulations of various salts containing appropriate percentages of the elements.

Ammonia can be used to manufacture ammonium salts and nitric acid.

Potassium chloride, potassium sulfate and phosphate rock are obtained by mining, but phosphate rock cannot be used directly as a fertiliser.

Phosphate rock is treated with nitric acid or sulfuric acid to produce soluble salts that can be used as fertilisers.

Students should be able to:

• recall the names of the salts produced when phosphate rock is treated with nitric acid, sulfuric acid and phosphoric acid
• compare the industrial production of fertilisers with laboratory preparations of the same compounds, given appropriate information.

AT 4

Prepare an ammonium salt.