Science at key stage 3    (Year 9)

• Show pupils a video/video clip or other secondary sources of a range of fuels burning, and ask them what they recall about the sort of materials that are fuels and what is made when they burn. Demonstrate products (carbon dioxide and water) of burning natural gas. Ask pupils to explore, using secondary sources and practical work, what is formed when other fuels containing hydrogen and carbon, eg ethanol, wax, wood, burn.
• Establish the products of complete combustion as carbon dioxide and water, and that soot and carbon monoxide can also be formed. Extend by asking pupils to find out about the use of hydrogen as a fuel and its advantages and disadvantages.

• Tell pupils that the chemicals found in match heads are potassium chlorate, sulphur and carbon and give them a series of questions to answer, eg
• Which of these are elements?
• What is the formula for potassium chlorate?
• What is its role?
• How does striking a match produce heat?
• What burns?
• Ask pupils to explain their answers.

• Extend ideas about using energy from chemical reactions by asking pupils to use secondary sources to find out about 'chemical heaters' for meals or hand warmers for climbers and explorers.
• Ask pupils to think about the type of reactant and reactions that would be effective and safe and discuss this with them. Provide them with the reactants to explore energy produced by some of these reactions. Ask pupils to draw up a specification for making a 'chemical heater' or an advertisement for a heater. Before they do so, ask pupils to think about the different ways in which similar information would be used in the two tasks. Help pupils to compare a specification and an advertisement and identify and explain why the formality of the writing is different in each case.

• Ask pupils to suggest other examples of situations in which chemical reactions are used as energy resources. If necessary, remind them of the thermit reaction. Demonstrate or ask pupils to explore the generation of a voltage from simple voltaic cells. Remind them of the reactivity series of the metals and ask them to predict pairings of metals that will give relatively high and low voltages and to test their predictions.
• Remind pupils of their investigation of the reactivity of magnesium and zinc in unit 9F 'Patterns of reactivity', and ask them to carry out quick test-tube reactions to compare the temperature changes when different metals are added to solutions of a salt, eg copper sulphate, ensuring they make a reasonably fair comparison. Discuss results with pupils, record word equations and, where appropriate, symbol equations for the reactions, and the key points relating energy produced to differences in reactivity.

• Use photographs, packaging, video material to illustrate to pupils the vast range of materials, including those in living systems, resulting from chemical reactions. If possible, invite a scientist, eg pharmacist, materials scientist, food scientist, to talk to pupils about what they do and how they develop new products. Supplement this by providing pupils with case studies of the development of a new product, eg drug, plastic, textile, foodstuff. Ask pupils to choose a product and make a summary of the key stages of development.

• Provide pupils with statements, eg
• Chemical reactions can be used as energy resources
• Chemical reactions are used to make new materials
• Chemical reactions are important in biological systems
• Give pupils a variety of information, eg description of photosynthesis, description of a plastic, diagram of a voltaic cell, word equations, symbol equations, and ask them to agree to which statement each piece of information is best assigned, and to identify whether any can be assigned to more than one category. Help pupils to make a summary illustrating the important uses of chemical reactions in everyday situations.

• Demonstrate some reactions in which a change can be clearly observed, eg production of a precipitate, change in colour, perceptible rise in temperature, but in which no gas is produced, and help pupils to devise a method for finding out whether there is a change in mass when the reaction takes place. Establish that mass is conserved.
• Take some examples of reactions, eg burning hydrogen; burning carbon to form carbon dioxide and to form carbon monoxide; combining hydrogen and chlorine, and model the rearrangement of atoms in these using, eg ball-and-spoke models, simulation software. Establish with pupils that atoms 'left over' cannot disappear.
• Help pupils to explain conservation of mass in terms of the rearrangement of the atoms during a reaction.

• Challenge pupils to decide whether mass would be conserved during a reaction in which a gas was made and, if possible, demonstrate this, eg by collecting gas in a syringe. Provide pupils with a number of descriptions of burning, eg it all turns into ash, nothing is left, the wood just shrivels away, and ask them to reconcile these with the idea of conservation of mass.

• Remind pupils of work they did earlier about making compounds from elements. Either demonstrate or ask pupils to find the increase in mass when magnesium burns in air. Compile a set of results from the class or provide pupils with a set of results and help them plot a graph of mass of magnesium oxide against mass of magnesium. Ask pupils a series of questions to elicit their ideas about what has happened, eg
• Why does the magnesium oxide weigh more than the magnesium?
• How much magnesium oxide is formed from 1g/1.5g of magnesium?
• How much magnesium oxide do you think would be formed from 10g/15g of magnesium?
• Do these results conflict with the idea of conservation of mass?

• Show pupils a wax candle burning and pose a question, eg If materials combine with oxygen when burning, why does a candle get smaller and smaller? Provide pupils with additional information, eg wax is a compound of carbon and hydrogen, and ask the pupils to suggest what is formed when it burns. Establish with pupils what is likely to be formed when hydrocarbons are burned and ask them to suggest what happens to the products.
• Represent the formation of carbon dioxide and water by word equations and/or diagrams. Extend to a range of compounds containing hydrogen and carbon, eg natural gas, sugar.
• Provide pupils with information about Priestley, Lavoisier and the phlogiston theory of burning, together with a series of questions of various difficulty, eg
• What did Priestley find out about oxygen?
• What was the phlogiston theory?
• What did Lavoisier contribute to the development of ideas about burning?
Ask pupils to describe what they found out and discuss with them eighteenth-century ideas about burning and how these differ from those we hold today. Ask them how our ideas about particle theory help to explain our views.

• Provide pupils with word equations and/or symbol equations, general equations and descriptions of reactions, eg neutralisation, combination with oxygen, displacement, and ask them to group together similar reactions. Include some that don't fit into any category. Discuss these and the classifications with pupils and agree with them a short list of key points about reactions, eg
• new materials are made
• atoms combine in different arrangements
• evidence for reaction includes ...
• mass is conserved because atoms link together in different ways
• chemicals are an energy resource because energy is often released when reactions occur