Common misunderstandings and misconceptions There are few areas of misconception in this topic. Students need to aware of the procedures involved and be careful in their drawing of the apparatus for various techniques.
Homework ideas ◆ ◆
End-of-chapter questions 6 and 7 and Questions 5.34 to 5.38 in the Coursebook Students can practise the analysis of titration results using Exercise 5.6 The analysis of titration results.
Topic 10
Preparing insoluble salts
Coursebook section 5.10 (pp. 141–143)
Teaching ideas ◆ ◆ ◆
The preparation of an insoluble salt by precipitation needs to be demonstrated and the procedure carried out by the students. There is opportunity to discuss and revise the solubility rules for salts. The use of the quantity of precipitate formed in the calculation of the formula of a salt should be practised.
Common misunderstandings and misconceptions The idea that some salts are insoluble and the preparation methods are straightforward but students can have difficulty with remembering which salts are insoluble and with the calculation method.
Homework ideas ◆ ◆
Exercise 5.8 Deducing a formula from a precipitation reaction Coursebook question 5.39
Topic 11
Strong and weak acids and alkalis
Coursebook section 5.11 (pp. 143–147)
Teaching ideas ◆
◆ ◆
The work on acids and alkalis can be extended to discuss the nature of and distinction between strong and weak acids (and alkalis), introducing the idea of partial ionisation. The concept of partial ionisation of a covalent molecule will already have been raised in discussing the nature of water. These ideas can be linked to a discussion of reversible reactions. The practical consequences of an acid being weak are illustrated in Activity 10.4 The acidic reactions of ethanoic acid where this acid is compared with hydrochloric acid in a series of reactions. More sophisticated definitions of acids and bases can be elaborated.
Common misunderstandings and misconceptions The conceptual difficulties arise when discussing the topic of weak and strong acids/alkalis. The practical demonstration of the differences between solutions of, say, hydrochloric acid and ethanoic acid are important in showing the reality of the distinction between a strong and a weak acid (Activity 10.4 The acidic reactions of ethanoic acid).
Homework ideas ◆
Coursebook questions 5.40 to 5.46 and End-of-chapter question 2
Original material © Cambridge University Press 2014 © Cambridge University Press 2014 IGCSE Chemistry
Teaching ideas: Chapter 5
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