Common misunderstandings and misconceptions Although the basic understanding of a chemical reaction may be relatively straightforward, as is the use of word equations, the technique of balancing equations proves problematic for some students. As mentioned earlier, the key is to develop some confidence in handling some of the less complex examples before building up the level of difficulty.
Homework ideas ◆ ◆
Worksheet 4.2 Balancing chemical equations Coursebook questions 4.4 and 4.5
Topic 3 Types of chemical reaction Coursebook section 4.3 (pp. 94–99)
Teaching ideas Survey the important types of chemical reaction. Define redox in terms of oxygen transfer. Discuss the further definitions of redox reactions. ◆
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The aim here is to demonstrate, or get the students to carry out, some of the different types of chemical reaction. This can be made quite interesting to the students and can be used to intersperse the ‘theoretical’ treatment of the work on chemical equations. The key types of reaction can all be introduced but some focus is placed on the important topic of the different definitions of oxidation and reduction; focus here on the definition in terms of oxygen loss or gain. Again, there is good scope for practical examples to help reinforce the ideas. The terms ‘oxidising agent’ and ‘reducing agent’ need to be carefully introduced alongside the idea of an overall redox reaction.
Common misunderstandings and misconceptions Most of the definitions for the different reaction types are clear-cut, even allowing for the fact that some reactions can fall into several categories. The most complex ideas here relate to the definitions of oxidation–reduction and the use of the terms ‘oxidising agent’ and ‘reducing agent’.
Homework ideas ◆ ◆ ◆ ◆
Worksheet 4.3 Different types of chemical reaction and Worksheet 4.8 Types of chemical reaction Exercise 4.2 The action of heat on carbonates and Exercise 4.4 Displacement reactions of the halogens Questions 4.6 to 4.8 and End-of-chapter questions 2, 3, 4 and 7 from the Coursebook are useful in this context. The photochemical reactions of silver halides are discussed in Worksheet 4.5 Film chemistry while Exercise 4.5 Self-heating cans, hand warmers and cool packs shows some novel uses of chemical reactions.
Topic 4 A closer look at reactions, particularly redox reactions Coursebook section 4.4 (pp. 100–102)
Teaching ideas ◆ ◆ ◆ ◆
Extend the definition of redox to include the loss or gain of electrons and change in oxidation state. The use of the mnemonic ‘oil rig’ is clearly of benefit. The use of oxidation state here is quite limited but relevant to the naming of various compounds. Include in your discussion the tests for, and definitions of, oxidising and reducing agents. The displacement reactions of the halogens are useful here, while the thermit reaction provides a spectacular demonstration.
Common misunderstandings and misconceptions The most complex ideas here relate to the different definitions of oxidation–reduction and their application to particular examples. It is important to maintain clarity in the presentation of the different examples. The use of the mnemonic ‘oil rig’ related to the definition in terms of electrons is very familiar, but remains very effective. Original material © Cambridge University Press 2014 © Cambridge University Press 2014 IGCSE Chemistry
Teaching ideas: Chapter 4
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