Science at key stage 3    (Year 7)

• Provide pairs of pupils with everyday materials which react chemically when they are mixed, eg lemon juice and bicarbonate of soda, baking powder and water, plaster of Paris and water. Ask pupils to mix them and make as many observations as they can. Ask pupils to decide and give their reasons for whether a new material has been made. Explain that in each case a chemical reaction has taken place and that in this unit they will find out more about other chemical reactions and what new substances are made.

• Remind pupils of earlier descriptions of acids as corrosive and show some examples of corroded metals. Establish through a quick class experiment that when an acid is added to a metal, eg zinc, magnesium, bubbles are made.
• Demonstrate an appropriate method for testing the gas produced and explain that a gas behaving in this way is hydrogen.

• Ask pupils to investigate what happens when a range of acids is added to a range of metals and to record and make generalisations from their results.
• Bring together pupils' results and establish that in most cases a new material, hydrogen, is made, showing that there was a chemical reaction between the acid and the metal.

• Ask pupils what the 'fizz' in bottled water is. Identify the gas as carbon dioxide and demonstrate how to collect carbon dioxide and test for it using lime water.
• Provide pupils with samples of carbonate, possibly including rocks, eg chalk, building materials, eg marble, household materials, eg baking powder, carbonate indigestion remedies, and ask them to investigate the effect of adding a range of acids to these and to record and make generalisations from their results. Establish that in each case a chemical reaction took place and draw out the idea that chemical reactions are important.

• Demonstrate burning some elements in air and then in oxygen. Emphasise the hazards of burning materials in oxygen. Use secondary sources to illustrate more hazardous reactions. Show pupils how to burn materials safely in oxygen. Ask pupils to describe what they see and point out to them that in each case the new material is an oxide and that a chemical reaction has taken place.
• Introduce the idea of word equations for simple combustion reactions and ask pupils to sort cards showing reactants and products to produce word equations.
• Ask pupils to use secondary sources to find information about fire prevention and firefighting and to produce information sheets, eg for use in the home, explaining key principles.

• Provide pupils with a series of cards showing words or phrases about the chemical reactions, eg reactant, product, metal, acid, carbonate, oxide, carbon dioxide, hydrogen, oxygen, and ask them to group them into three sets to describe the three types of chemical reaction covered in the unit. Help them to use the words or phrases to make generalisations about the three types of reaction.

• Elicit pupils' ideas about fuels by asking them what they understand by the term and what examples they can give of fuels. Explain that fossil fuels are rich in carbon and ask pupils to suggest what might be formed when they burn.
• Demonstrate that carbon dioxide (and water) is produced when methane burns. If possible, extend the demonstration by using other fuels containing hydrogen and carbon, eg wax, ethanol, wood. Discuss with pupils whether it is likely that carbon dioxide and water could be turned back into fuel.
• Help pupils make a summary of information about burning fossil fuels.

• Show pupils the effect of putting a large glass container over a lighted candle floating on a trough of water and ask questions to help them explain what happens, eg
• What was in the large container?
• Why did the candle go out?
• Why didn't it go out immediately?
• Why did the water rise up the container?
• What is made when a wax candle burns?
• What happens to this?
• Ask pupils in groups to work out explanations. Help them to evaluate their explanations through questioning and establish that part of the air was used up and that the candle could not continue to burn. Link back to earlier work on comparing burning in air and oxygen.
• Extend by asking pupils to investigate the idea that the candle goes out when part of the air is used up. Help them to turn this into a question that can be tested and to devise a way of getting results from which a graph can be plotted.

• Provide pupils with a series of statements, or ask them to make their own, about the areas covered in the unit. Ask them to work together to choose the most helpful statements for a summary and to group those chosen into four or five main sections. Ask pupils to explain why they chose or rejected particular statements and agree an overall summary with them.