Can we make predictions about the reactions of metals with oxygen?

•   to use a proposed reactivity series to make predictions

•   to test predictions made

•   that metals react with oxygen to form oxides 

•   Remind pupils that metals also react with oxygen (or the oxygen in the air) to form oxides. Ask them about word equations. Ask pupils to use their proposed reactivity series to suggest how readily different metals would react, and then use a mixture of demonstration and video clips to test whether the predictions are supported. Point out that in establishing a reactivity series, more secure evidence than qualitative observations is needed. Establish with pupils that, in terms of the evidence collected, the order of reactivity of metals with oxygen is generally similar to that with water and with acids.

•  use the reactivity series to make a sensible prediction,
eg sodium would be more reactive with oxygen than copper

•  evaluate the evidence obtained, eg magnesium reacted more violently than copper, but it was difficult to compare sodium and calcium

•  state that all the metals tested produced oxides

•   Extension: some pupils may be ready to look at quantitative data supporting an established reactivity series. In unit 9I ‘Energy and electricity’ pupils explore the voltage of simple cells with poles made from different metals.

•   Extension: pupils could be asked to write the symbols and formulae for reactants and products, and from these write symbol equations.

Safety

– magnesium and some other metals are highly flammable. Risk as­sessments should be followed. Eye protection should be used. Avoid looking directly at burning magne­sium. Safety screens should
be used

    Can metals displace each other?

•   that a metal will displace a less reactive metal from a solution of one of its salts

•   to construct a table to show patterns clearly

•   to identify patterns in observations

•   to use a model to explain results 

•   Provide pupils with small samples of metals, eg magnesium, iron, copper, zinc, and solutions of metal salts, eg zinc sulphate, iron (II) sulphate, copper sulphate, silver nitrate. Ask pupils to plan tests of combinations of metal and metal salt to find out if there is a reaction, recording their results in a table. Ask pupils to find a pattern in their results and, if possible, to reorder their table to show the results more clearly. Discuss the results with the pupils and use an analogy or model to explain the displacement of the less reactive metal by the more reactive one. Ask pupils to predict whether other reactions will occur.

•   Show using an analogy, eg ‘pull’ of metal on the sulphate, and word or symbol equations that whether there is a reaction or not depends on the metal and the metal in the salt, not on the acid from which the salt was derived.

•   If appropriate, link to work pupils have done on the voltages of simple cells.

•  identify where reactions occur and where they do not

•  relate their results to the position of the metal in the reactivity series

•  articulate the pattern, eg it’s the metal that’s important; a metal high in the reactivity series will push out one lower down, but a lower one won’t push out a higher one

•  use an analogy or model to explain the results, eg the zinc has a stronger pull on the sulphate than the copper does

•   Using very small quantities in a dimple tile works well. In some cases, eg if magnesium is added to copper sulphate solution, the reaction may be between the water and the metal rather than between the salt and the metal.

•   This activity provides an opportunity to use ICT to reorder tables of results.

•   This work could be extended to heating metals, eg copper, zinc, with metal oxides to determine whether there is a reaction. Some mixtures may be dangerous.

•   Although analogies, eg ‘pull’ of metal, are not strictly correct, they may be helpful to pupils in establishing principles about displacement.

•   Extension: pupils could be asked to write the symbols and formulae for reactants and products, and from these write symbol equations.

Safety

– 0.4 mol dm^-3  or 0.1 mol dm^-3  solutions of salts can be used.
Eye protection should be worn.

– appropriate risk assessments
should be followed before practical work begins

•   that displacement reactions can be useful

•   Demonstrate the thermit reaction between iron (III) oxide and aluminium. Ask pupils to explain where the energy to melt the iron produced comes from, and explain, eg using a video clip, the use of the reaction in welding. Use the displacement model to describe what is taking place during the reaction.

•  explain that energy released by the reaction is sufficient to melt the iron

•  describe how molten iron is used in welding, eg on railway lines

Safety

– an appropriate method should be used and a risk assessment followed. Safety screens and face shields should be used

     Checking progress

•   how an activity series can help to make sense of the reactions of metals

•   how an activity series can be used to make predictions

•   that sometimes the data doesn’t enable firm predictions/ conclusions to be made 

•   Provide pupils with an activity series of metals (including some that they haven’t tested, eg aluminium, lead, silver) and help them make a summary sheet showing reactions of the metals.

•   Tell pupils the position in a series of an unknown metal and ask them to predict its reactions. Give pupils information about the reactions of metals not already in the series and ask them to predict where they might come.

•   Discuss with pupils any difficulties in coming to decisions.

•  summarise reactions of metals, making use of patterns in the reactivity series

•  use the activity series to make predictions about the reactions of metals

•  identify where an element cannot be given a position or where a firm prediction cannot be made, giving reasons for the difficulty 

•   Extension: some pupils could be given quantitative data.

    How does the activity series relate to uses and sources of metals?

•   to identify what information is needed, and use different texts as sources

•   to structure paragraphs to develop points, using evidence and additional facts

•   to relate the occurrence, extraction and use of metals to their position in the activity series

•   Introduce the activity with a short video illustrating the range and uses, and possibly extraction, of metals.

•   Ask pupils to use secondary sources, together with their own knowledge of metals to find the answers to a series of questions of varying difficulty, eg

– Why is sodium not used for cutlery?

– Why is a light metal like magnesium not used for car bodies?

– Why has so much gold jewellery survived from ancient civilisations?

– Why was bronze used before iron?

– Aluminium is much more abundant than iron, so why wasn’t it used until the beginning of the twentieth century?

– Which metals are found naturally?

– What are the sources of magnesium? Why is it not found naturally?

– How are metals recycled?

•   Ask pupils to present their findings and help them to organise the points to produce an information leaflet linking metals’ reactivity to their uses (including when they were first used).

•  identify key points relevant to the questions asked

•  make connections between reactivity and aspects of use, eg aluminium is reactive, and therefore hard to extract – this is why it wasn’t used as early as iron

•   In unit 9E ‘Reactions of metals and metal compounds’ pupils will have found out something about uses and sources of metals. This activity extends that work by relating it to the reactivity series.

•   Pupils should be encouraged not to look in too much detail at extraction processes, but to identify the key point about the method, eg electrolysis, smelting with carbon.

•   Information about copper can be found on the internet, eg at www.copper.org

    How can we find out more about the reaction of metals with acids?

•   to decide which observations or measurements are appropriate

•   to identify variables that need to be controlled and decide how to do this

•   to choose axes and scales for graphs

•   to decide whether results that do not fit the pattern expected arise from experimental shortcomings or are significant

•   to explain results in the light of scientific knowledge and understanding 

•   Review what pupils remember about the reactions of acids with metals and remind them of how they compared their reactivity. Explain that they are going to investigate more systematically the differences in reactivity of zinc, magnesium and aluminium with hydrochloric acid. Discuss the indicators, eg changes in temperature, amount of gas produced, that might be measured and which variables they will need to control. Help pupils plan and carry out their investigations safely and, where appropriate, present their results as graphs. Ask pupils to tell the story of what the graphs show and to explain whether the results are what they expected from the relative positions of the metals in the reactivity series. Remind them of earlier work on the extraction of aluminium. Discuss with pupils the key points in this investigation and help them to write an account that brings these out clearly.

•  identify a workable procedure, eg to measure the temperature of the reacting mixture every minute for 10 minutes

•  identify variables that need to be controlled, eg quantity of metal, volume of acid

•  present results clearly and appropriately

•  explain the results obtained in the light of the reactivity series and knowledge about aluminium

•   If pupils devise their own methods for this investigation, they may choose measures that compare the rates of the reactions rather than the reactivity of the metals. Some teachers may wish to discuss this with some pupils.

Safety

– 0.4 mol dm^-3 acid and coarse-mesh filings of the metal can be used. Eye protection should be worn. Coarse-mesh magnesium and aluminium are highly flammable. Supervise this investigation closely

– pupils’ plans should be checked for health and safety before practical work begins

    Reviewing work

•   key ideas about the relative reactivity of different metals

•   how to apply the ideas

•   how to recognise what information questions are seeking and to evaluate answers 

•   Prepare a short test on the content of the unit, eg using comprehension and data-handling questions about different metals, together with additional questions to provide practice materials. Discuss the additional questions with pupils, eg by asking them to read questions out loud, discuss what the questions mean and what sort of answers are required before they take the test. When pupils have taken the test and it has been marked, discuss their answers to the test questions in a similar way. Provide real (or made-up) answers to some questions and ask pupils to identify good and bad points in each.

•  recall key ideas about the relative reactivity of different metals

•  use and apply these ideas in different contexts

•  identify how sample answers provide, or do not provide, the information required