WJEC Chemistry for AS Level Student Book: 2nd Edition

On pp1–2 of the WJEC lab book is a spreadsheet with a list of the speci ed practical tasks. The rst twelve practicals relate to the AS course. Read the Guidance Notes (pp3–4) in the WJEC lab book every time you do an experiment. It will not take long for you to become familiar with them. They tell you about experimental design, risk assessments, how to display readings and how to plot graphs. They also list aspects of the analysis of your results. It is important to undertake all twelve practicals, as you may be asked about these, or very similar, experiments in an examination. You should write the date that you did the experiment. There is space for notes and comments. Use this space to remind you of particular issues that occurred to you, so that when you revise for your examinations, you will remember aspects of the experiments that you found signi cant or challenging at the time. This book will also help you develop your practical skills and understanding of experimental chemistry. The speci ed tasks are discussed in detail in the relevant chapters. In addition, advice is given on how to improve a method and how to analyse and evaluate the results. Assessment Assessment objectives Examinations test your subject knowledge and the skills associated with how you use that knowledge. These skills are described in Assessment Objectives. Examination questions are written to re ect these objectives, with marks in the proportions shown: AO1 AO2 AO3 AS Level 36.2% 43.8% 20% You must meet these Assessment Objectives in the context of the subject content, which is given in detail in the speci cation. Your ability to select and communicate information and ideas, clearly using appropriate scienti c terminology will be tested within each Assessment Objective. The Assessment Objectives are explained below, with examples of how they are tested. The mark schemes for these questions are on page 214. Assessment Objective 1 (AO1) Demonstrate knowledge and understanding of scienti c ideas, processes, techniques and procedures. This AO tests what you know, understand and remember. It is a test of how well you can recall and explain what is relevant. That is why it is essential that you know the content of the speci cation. The questions that test this AO are often short-answer questions, using words such as ‘state’, ‘give’, ‘explain’ or ‘describe’. Here are two examples: AO1 Demonstrate knowledge Give the meaning of the word electronegativity . [1] This question tests AO1 because it asks you to recall factual information. AO1 Demonstrate understanding of scienti c ideas Explain why a change in concentration affects the rate of a reaction. [2] This question tests AO1 because it asks for an explanation based on your factual knowledge. Assessment Objective 2 (AO2) Apply knowledge and understanding of scienti c ideas, processes, techniques and procedures: ▪ in a theoretical context ▪ in a practical context ▪ when handling qualitative data ▪ when handling quantitative data. AO2 tests how you use your knowledge and apply it to different situations, in the four possible ways shown above. A question may present you with a situation that you may not have met before, but it will give you enough information so that you can use what you already know to provide an answer. Make sure you understand the methods of all the experiments you have done; the tests for cations and anions in inorganic chemistry; the tests for functional groups in organic chemistry. Be sure you understand how to do all the calculations needed to process the results. In testing AO2, a question may have command words such as ‘use your knowledge of…’, ‘calculate’ or ‘explain…’. Here are four examples: AO2 In a theoretical context Use ideas that you have studied in your Chemistry course to comment on and explain the following observation. When dilute sulfuric acid is added to aqueous magnesium chloride no visible change occurs but when it is added to aqueous barium chloride a white precipitate is observed. Include an equation for any reaction that you observe. [3] ‘Use ideas that you have studied’ indicates that you should use your theoretical knowledge and understanding to explain a chemical observation. AO2 In a practical context A compound is known to be one of butan-2-ol, CH 3 CH 2 CH(OH)CH 3 , 2-methylpropanoic acid, CH 3 CH(CH 3 ) COOH, and 3-hydroxybutanoic acid, CH 3 CH(OH)CH 2 COOH. 6 WJEC Chemistry for AS Level