Chemical Reactions: combustion, thermal decomposition, oxidation and displacement
KS3 practical resources for chemical reactions, including some exciting demos of oxidation, combustion and decomposition.
Visit the practical work page to access all resources and lists focussing on practical work in secondary science: www.nationalstemcentre.org.uk/sciencepracticals
Flaming Hand
This makes a great attention grabbing start to a lesson about combustion reactions. Once students have seen and experienced for themselves the explosive reaction, the teacher can go on to talk about the fire triangle and discuss the word equation for the reaction. You can also introduce the term “exothermic” since students will have felt for themselves the heat energy released.
The demo has been successfully carried out just wetting the hands thoroughly with water rather than covering them with washing up liquid which takes more effort to remove.
Be sure to keep the hands at arm’s length; there can be a tendency to pull the hands away from the flame and towards the body. Of course the flame comes too and then there’s a risk that hair can get caught in the flame.
The whoosh bottle (see next resource) is a lovely follow on as the products of the reaction are more obvious.
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Whoosh bottle
This favourite demonstration follows on very well from the flaming hand demo and is an excellent illustration of a combustion reaction.
There's no need to use propanol as suggested in the film as IMS/meths works just as well, if not better, and is much cheaper. As you prepare the bottle, discuss the mixing of the vaporised fuel with oxygen and be sure to make sure the class see you pour away the excess liquid fuel. When you light the fuel make sure it isn't too close to the ceiling and ensure the bottle isn't underneath a projector.
After the combustion reaction the bottle can be passed around the class so students can feel how warm it is. You can demonstrate the presence of carbon dioxide as a product of the reaction by showing that a lit spill goes out if placed in the bottle. Pouring out the condensed water (without soot if you use meths!) is effective for showing the other product of the reaction.
Students should now be able to write a word equation for the combustion reaction and go on to predict the equations for other fuels. If you have a second bottle, the reaction can be shown again at the end of the lesson if students work well enough! If you don't already have a suitable bottle in school, they can be bought via the internet at modest cost.
ChemWars *suitable for home teaching*
Visualising displacement reactions as a "fight" between two elements helps to make the concept more concrete for students and this resource shows the fights as a Sumo wrestling match between metals. The animation can be worked through individually if you have access to a computer suite but a teacher led discussion with the whole class watching via a projector can work equally well.
There are videos of each reaction to show but allowing students to carry out the reactions for themselves is always recommended. Having discussed the reaction beforehand, students will get more from the experiment as they will know what they are looking for. Again students should be able to write word equations and be able to find patterns in the results. You can find practical details and equipment lists in the accompanying documents.
Stuff and Substance: Ten Key Practicals in Chemistry *suitable for home teaching*
Activity A8 in this SEP booklet (page 31) gives details of how the oxidation of magnesium could be taught. Students can readily carry out the oxidation of magnesium ribbon for themselves, and the nice extra here is a teacher demonstration which adds a bag of oxygen to the equipment. Students will be able to watch the oxygen being used up as the reaction progresses.
Part 3 of the presentation includes some slides (slides 7, 8 and 9) which teachers might like to use. Slide 9 which shows the structures of the chemicals before and after the reaction is particularly useful and links to the ideas of elements and compounds. There is a student worksheet available in both pdf and word versions. Teachers may like to spend some time reading through the SEP booklet. It is well written and helpful for when explaining key chemical ideas about particles and reactions to students.
Demonstrating Chemistry: The Science of Fireworks *suitable for home teaching*
The first half of this film shows some lovely chemical reactions, including oxidation and combustion reactions, in the context of fireworks. (The second half of the film still uses fireworks but is based around physics.) Teachers might like to base their teaching of this section of the national curriculum around this topic as it is likely to generate considerable interest and enthusiasm from the students.
Although the film only shows a teacher carrying out the reactions, there is no reason why students shouldn't carry out some of them for themselves, for example, gently sprinkling iron filings into a Bunsen flame. Students could "write up" this work by preparing a leaflet on the chemistry of fireworks that might go in each box of fireworks sold.
