Common misunderstandings and misconceptions There are no substantial misunderstandings or misconceptions here. The main difficulty lies in students failing to give sufficiently comprehensive answers to questions in the tests. Stress the need to give the colour before and after the test when describing a colour change. Also stress the need to describe the negative result when comparing, say, the result of the bromine water test on an alkane and alkene.
Homework ideas ◆
Coursebook questions 12.10 to 12.12, p. 305 and End-of-chapter question 5 indicate the type of question that can be asked on testing for organic substances.
Topic 3
Experimental design and investigation
Coursebook section 12.3 (pp. 305–310)
Teaching ideas ◆
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In the early stages of the course, use questioning to find out the learners’ current understanding of what these measurements mean, and what units are involved. Possibly play a game of ‘Name that apparatus’ in small teams of students. Provide students with a number of challenges to help them choose the most appropriate equipment to measure a certain amount., e.g. ‘Bring me 20 ml of water’, ‘Bring me 1 g of salt’, etc. Students practise using the equipment with a ‘circus’ of activities to include measurements of temperature, volume, mass and time in the laboratory. Provide guidance and opportunities for the design, investigation and evaluation of practical activities. The comments made earlier in the notes for this chapter are again relevant.
Common misunderstandings and misconceptions The most common errors when handling measuring equipment in the laboratory include: ◆ ◆ ◆ ◆ ◆
time recorded in minutes and seconds, rather than seconds only correct use and positioning of a decimal point when measuring small masses in grams understanding the graduations on thermometers, burettes and measuring cylinders selecting a beaker rather than a measuring cylinder for recording volumes – students need general guidance on the relative accuracy of graduated glassware general misuse of correct units.
Students find the area of planning and evaluating experiments difficult – often resorting to very generalised comments about ‘fair testing’. The ideas involved should be broached and developed over an extended period. To assist with this, a range of resources is listed here which can be drawn on at these various points during the course. These are areas of practical work that students can find rewarding. However, they may detract from their achievement by lazy and unskilled presentation of diagrams, tables and graphs. The exercises in the Workbook coupled with the self-assessment tables given there are intended to help students to be more disciplined in these areas. The use of IT packages to assist with data logging and presentation is one area that may generate additional interest in students and help with the evaluation of data. However, it should be remembered that students will have to work ‘by hand’ in examinations, so they cannot leave aside the development of these skills.
Homework ideas ◆ ◆
Use the examples given in the end-of-chapter questions, the Model Paper 6s and the exercises in the Workbook to familiarise students with the types of question they will meet in the examination. The exercises presented in Chapter 12 of the Workbook are specifically designed to cover the type of questions on planning and evaluation that can now occur on both the practical papers (Papers 5 and 6) of the exam: Exercises 12.3 Planning a controlled experiment, Exercise 12.4 Chemical testing and evaluation and Exercise 12.5 Experimental design.
Original material © Cambridge University Press 2014 © Cambridge University Press 2014 IGCSE Chemistry
Teaching ideas: Chapter 12
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