Chemistry Teacher Practical Guide

INTERNATIONAL ADVANCED LEVEL

CHEMISTRY EDEXCEL INTERNATIONAL GCSE

ECONOMICS

TEACHER SPECIFICATION PRA PR A CT CTIC ICA A L GU GUID IDE E

Edexcel International GCSE in Economics (9-1) (4ET0) Pearson Edexcel International Advanced Subsidiary in Chemistry (XCH11) First examination June Pearson Edexcel International Advanced Level in Chemistry (YCH11) First teaching September 2018 First examination from January 2019 First certification from August A ugust 2019 (International Advanced Subsidiary) Subsidiary) and August 2020 (Internationa ( Internationall Advanced Level)

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Contents Introduction Practical assessment – the whole picture Preparing students for questions assessing practical understanding Core practicals Using Core Practicals to Teach Skills Progression Planning practical lessons Developing maths skills through core practicals Accuracy and errors in practical work Opportunities for development of maths skills Teaching approaches to core practicals Commentary on the Core Practicals Research and referencing Independent thinking and evaluation Chemical analysis Answers to Student Guide Questions Answers to Core Practical questions

4 5 6 12 13 14 14 15 17 18 19 20 27 28 29 36 38















Introduction This guide is designed to: 1. support you and your students through all elements of practical work in the new International AS and A level specification. Although it will address assessment arrangements, its focus is to ensure good quality practical work is at the heart of teaching and learning in the subject, 2. explain how the new requirements for practical skills can be developed throughout the course using both core practicals and other specification content. The over-arching aim of the specification is to help learners progress from being International GCSE/GCSE students towards becoming ready for the next stage of their development, whether that be university or the workplace. To some extent this can be through developing skills such as non-routine problem solving and ICT literacy but also by personal skills in communication, adaptability and self-management. In terms of practical work, the aim is for students to become b ecome capable of thinking independently. Part of this is developing confidence in their own competence to challenge accepted practice and ask ‘How do I know that?’ , whilst thinking about the science behind the observations. This may be exhibited by e.g. working towards thinking independently in planning and evaluating for themselves the outcome of practical work. Over the course of the new International A level, students will develop a range of skills in practical work. This will vary from the acquisition of specific practical techniques in a range of experiments (the use of a burette or assembling apparatus for carrying out a distillation), through to the development of some investigative techniques requiring independent thinking (planning and carrying out an experiment to determine the effect of a change in concentration of a reactant in an unfamiliar reaction). At one level, practical work undertaken by b y students can be simple, perhaps focusing on observational aspects of the subject (such as Core Practical 8: Analysis of some inorganic and organic unknowns), whereas other practical experiences may be truly experimental (such as Core Practical 9a: Following the rate of the iodine-propanone reaction by a titrimetric technique). Many experimental activities will involve the collection of quantitative data; and this provides opportunities for the development of mathematical skills, which are also required as part of the specification (see Appendix 6 of the specification). There is a students’ guide designed to be used alongside this teacher resource, which is written to explain the new requirements to your students in a straightforward way and to provide exercises to allow them to develop de velop their skills. You will find the suggested answers to these exercises are i ncluded in this teachers’ guide.















Practical assessment – the whole picture At first glance, the specification contains a number of references to practical p ractical work – both in terms of delivery and assessment – so it might be helpful, at the start of this Guide, to see what these are, and how they relate to each other. This is particularly important because, as a teacher of the subject, you will naturally want to focus most closely on what is best for your students in terms of skills development and exam preparation. The most obvious place to start is an assessment overview. Units 3 and 6 remain primarily focussed on the assessment of practical skills and each cover 10% of t he total international A Level specification. Unit 3 exam will assess candidate’s knowledge and understanding of experimental procedures

and techniques developed in Units 1 and 2. Unit 6 will also draw on these skills but also assess candidate’s knowledge and understanding

of experimental procedures and techniques developed in Units 4 and 5. These exam papers constitute the formal assessment of practical p ractical work. The assessment of the core practicals by teachers is of an informal nature and does not contribute to the A Level grade for the students but nonetheless the feedback to students will be invaluable in their preparation for examinations.

How do the core practicals cover the techniques and apparatus? As you will see from the list of core practicals on page 11, some of the techniques and apparatus will be covered several times; whereas oth ers may only be addressed once. This is useful because it gives you an idea id ea of which core practicals are especially important for students to complete.

How flexible are the core practicals? The core practicals represent our suggestion for ensuring that you cover the procedures and techniques witho ut having to worry. Of course, they aren’t the only way – so you are free to develop your own practical program. More commonly, you may find that one or two of the core practicals do not suit you, possibly due to resources, or because you have a preferred practical activity in a particular topic area. In this case, feel free to swap our core practical for one of your own. However, we would very much recommend that you did all the practicals that we specify – and, where time permits, more on top! Any practical work that your students attempt – not















Preparing students for questions assessing practical understanding In addition to the new Sample Assessment Materials (SAMs), (SAMs) , there are many suitable examples in past papers that could be used for students to prepare for this type of questions. Past papers are available on the Edexcel Edex cel website at both AS (Unit 3) and A level (Unit 6) standard.















Sample questions Here is a typical example form an International A level paper (WCHO3/01 January 2015).

































































Commentary This question could be set in either e ither Unit 2 or Unit 3 at AS level, testing the specification specification statement 10C, 10.17(ii): bromination of alcohols. Part (a) deals with possible side reactions; a useful teaching point since students often gain the impression, particularly particularly in Inorganic Chemistry, that only one set of products is possible for a given set of reactants. Parts (b) to (e) focus on the practical aspects of the preparation, asking questions on why and how various steps are carried out. Experience indicates that most students are adept at describing how to carry out preparations, but far fewer are capable of explaining why particular procedures are used. Part (f)(i) is a simple mass calculation that is not level 2 mathematics. Part (f)(ii) is a slightly more sophisticated calculation of percentage yield, with at least one mark at level 2 for the appropriate use of significant figures.

















Core Practicals The Core Practicals are an integral part of your course. They are not there to get you to demonstrate some text book 'fact' or recall some simple information. They are there to help you develop the whole range r ange of practical and mathematical skills which are essential to chemists and which will be tested in the written assessments.

List of Core Practicals 1. Measuring the molar volume of a gas 2. To determine the en thalpy change of a reaction using Hess’s Law 3. Finding the concentration of a solution of hydrochloric acid 4. Preparation of a standard solution from a solid acid and use it to find the concentration of a solution of sodium hydroxide 5. Investigation of the rates of hydrolysis of halogenoalkanes 6. Chlorination of 2-methylpropan-2-ol with concentrated hydrochloric acid 7. The oxidation of propan-1-ol to produce propanal and propanoic acid 8. Analysis of some inorganic and organic unknowns 9. Following the rate of the iodine-propanone reaction by a titrimetric method and investigating a ‘clock reaction’ (Harcourt-Esson, iodine clock) 10. Finding the activation energy of a reaction 11. Finding the K a value for a weak acid 12. Investigating some electrochemical cells 13. Carry out redox titrations with both:



















Using Core Practicals to Teach Skills The most important principle, which will be reiterated throughout this guide, is that the assessments stress the idea of developing skills. Whilst students are expected to have some knowledge of the techniques and procedures they encounter throughout the course, recalling small details is the simplest part of what is required. r equired. Developing skills implies that there is significant progression in terms of independent thinking and understanding of the underlying science behind what they are undertaking .

We have selected core practicals to be included in our specification that are accessible to all students and provide opportunities to develop d evelop the skills listed, and not because they are 'perfect' examples of experimentation or can be used to demonstrate a textbook 'fact'. In addition to the core practicals, p racticals, schemes of work need to include at least some of the experiments given in the introduction to each specification topic and in the topic i tself. For example in Topic 17: Transition metals.

Section

Practical work

In the laboratory

19

Reduction of vanadium(V) to vanadium(II) to show the colours of the oxidation states

22

Addition of NaOH(aq) and NH3(aq) to transition metal ions

As a teacher demonstration: Add Zn to an acidified solution of NH 4VO3 to show the changes in colour as vanadium is is reduced through its successive oxidation states On a test tube scale: add dilute NaOH(aq) and dilute NH 3(aq), until in excess, to the TM ions listed in 24.



















Progression Students beginning a two-year International A Level Chemistry course will have some experience of practical laboratory work from their International GCSE/GCSE studies. They will have developed some practical skills and be able to recognise and safely use simple laboratory equipment. They should be familiar with common laboratory substances such as dilute acids and alkalis and be capable of using these in practical work, paying due regard to the safety of themselves and of others. Students beginning the course should appreciate that there is a scientific method involved in Chemistry. They will have carried out enough practical work to understand that Chemistry has developed as a science on the basis of observations and measurements made in the laboratory. In their International A Level Chemistry course, students will build on the laboratory skills developed at GCSE. They will use more complex equipment and handle a greater range of substances. It is likely that they will spend more time carrying out practical work than at International GCSE/GCSE so will need to keep detailed records of their experiments.

Planning practical lessons It is a common belief that simply including practical sessio ns within the course is a ‘good thing’ which helps to motivate students. However, this is not always the case - as students will often say themselves! Like any other lesson, students are only engaged when they see clear aims and objectives which are relevant to their course. These aims must be relevant, achievable and explicit. As teachers, we know what is likely to happen during any one practical session. We also know that the time available for each practical is limited so it is vital to consider what w hat our main



















Developing maths skills through core practicals Full details of the mathematical skills requirements can be found i n Appendix 6 of the specification along with exemplification of each assessment objective. All of the skills are to be examined at level 2. ● ● There will be at least 20% of the marks awarded at Advanced Level and for Advanced Subsidiary Level for mathematical skills. ● Mathematical skills will be expected in papers for units 1, 2, 4 and 5.

What is meant by level 2 mathematics? Level 2 mathematics is of the standard of higher tier GCSE/International GCSE. The definition of level 2 can be affected by the context in which it is applied. For instance, where there is a great deal of structure or 'scaffolding' for a question then the demand is lower and may not be level 2. Simply providing a formula and a list of data which is carefully defined would involve only simple substitution and be unlikely to meet level 2. However, selecting which data to apply and which formula to use would. It is also useful to understand what is i s not regarded as mathematical skills. Questions often provide data from which students are expected to make conclusions by applying their chemical knowledge and understanding. Even though data may be involved this would not be regarded as mathematical skill. Similarly, simply defining mathematical terms or describing them would not be a mathematical skill. The new requirements for mathematics in all science specifications have obvious implications for planning schemes of work. It is common for chemistry teaching groups to contain students with varied mathematical ability and careful careful thought will be needed to meet their needs.



















Graphs The following are some useful points for students to consider when drawing graphs: ●

●

● ●

●

●

●

Put the dependent variable, the quantity being measured (e.g. temperature), on the y axis, and the pre-determined quantity (e.g. volume of solution) on the x -axis. -axis. Choose the scales so that the results are spread out as far apart as the size of the grid allows. However this should not be at the expense of using a sensible scale, e.g. using 1 cm on the axis to represent 3 or 4 units might spread the readings better than using 1 cm to represent 5 units, but the scale would be hard to read. In exams, the plots should cover at least half of of the grid supplied for the graph. Always label Axes should always with the quantity qu antity being measured and the units. These should be separated with a forward slash mark, e.g. time / time / s. Data points should be marked with a cross ( ), but care should be taken that data points can be seen against the grid. The origin (0, 0) does not need to be included on either scale if it is not relevant, for example if temperature readings between 21.0°C and 39.0°C are to be plotted there is no need to begin the y axis axis at 0. Rather it could be scaled from 20.0°C to 40.0°C. The line of best fit should be a continuous straight line, drawn with the aid of a ruler, or smooth curve (most likely drawn freehand, unles s a ‘flexicurve’ is available). Since the readings are all subject to experimental error the line drawn may not necessarily pass through every point. There is no definitive way of determining where a line of best fit should be drawn. A good rule of thumb is to make sure that there are as many points on one side of the line as the other. Often the line should pass through, or very close to, the majority of plotted points. Never join Points by a series of short, straight lines.

Significant figures



















Accuracy and errors in practical work Students need to understand the limitations of the equipment that they use in i n their practical work and be able to express errors and uncertainties quantitatively. It is essential that they are clear about the different terms associated with wi th accuracy and uncertainty. ●

● ● ●

● ●

Any piece of equipment used in i n a quantitative practical has a measurement uncertainty, however carefully it is used. The manufacturer of the equipment supplies the measurement uncertainty. The percentage uncertainty for a reading from the equipment may be calculated. A burette with an uncertainty of ±0.05 cm cm 3 for each reading is used to measure a volume of 24.50 cm3. For this reading,: 2 x 0.05 percentage uncertainty = × 100 = 0.41% 24.50 (In this case, the burette is used twice – to measure and initial and a final reading – so the uncertainty is doubled) Errors due to the apparatus are systematic errors . Uncertainties may be combined to find the total uncertainty in a final value calculated from experimental results. The results of a titration are used to calculate the molar mass of a compound as 126.0 g mol-1. The percentage uncertainties in the balance, pipette and burette readings used in the calculation are 0.12%, 0.25% and 0.55%. Total percentage uncertainty = 0.12 + 0.24 + 0.55 = 0.91%. 136 Total uncertainty in molar mass = 0.91 × = 1.15 100





















Opportunities for development of maths skills This grid shows how the core practicals can be used to develop mathematical skills within Chemistry; and also makes some links to the skills that may be tested indirectly (i.e. on written question papers).

Practical activity 1: Measuring the molar volume of a gas 2: To determine the enthalpy change of a reaction using

Mathematical skills 0.0, 1.1, 3.1, 3.2 0.0, 0.1, 1.1, 2.2, 2.3, 2.4

Hess’s Law

3: Finding the concentration of a solution of hydrochloric acid 4: Preparation of a standard solution from a solid acid 5: Investigation of the rates of hydrolysis of halogenoalkanes 6: Chlorination of

0.0, 0.1, 0.2, 1.1, 1.2 1.3, 2.2, 2.4 0.0, 0.1, 0.2, 1.1, 1.2 1.3, 2.2, 2.4



















Teaching approaches to core practicals The 16 core practicals should be used to allow students to develop their practical techniques and skills, and also to use their mathematical skills. It is expected that the course will wi ll include other practicals that also allow these techniques and skills to be introduced and practised but it is essential that the core practicals are given priority and emphasis. For example in Core Practical 4 students are to make up a standard solution of a solid acid and use it to find the concentration of a solution of sodium hydroxide. They may then go on to complete Core Practical 2 Finding the concentration of a solution of hydrochloric acid . There are experiments that may be included in the course before these two core practicals are set in order to give students the opportunity to practice the appropriate techniques. Students could make up a standard solution of sodium sodi um carbonate then use this, in a titration, ti tration, to find the concentration of dilute sulphuric acid. Most of the core practicals should be able to be carried out in i n one laboratory session. Some, however, will need a following session in order to be completed. For example in Core Practical 14 The preparation of a transition metal complex , crystals will have to be left overnight to dry out so that the yield may be accurately weighed.



















Commentary on the Core Practicals 1. Measuring of the molar volume of a gas This experiment provides opportunities for students to consider procedural errors and measurement uncertainties, and to identify changes that could be made to improve the accuracy of the results obtained. Procedural errors include placing the bung into the tube after the reaction has started and collecting the gas over water. Both lead to a loss of gas collected. There are three measurements taken: 1. the volume of ethanoic acid using a 50 cm3 measuring cylinder 2. the mass of calcium carbonate using a two decimal place balance 3. the volume of gas using a 100 cm3 measuring cylinder The percentage measurement uncertainty for each can be calculated and then a comparison can be made to decide which, if any, would produce the most significant effect when a change is made. For example, using a two decimal place balance, the measurement uncertainty for each



















3. Finding the concentration of a solution of hydrochloric acid

This is a straightforward titration using the standardised sodium hydroxide from Core Practical 4. Students could be asked to calculate the overall measurement uncertainty in their calculated concentration of hydrochloric acid. 4. Preparation of a standard solution from a solid acid and use it to find the concentration of a solution of sodium hydroxide

Before this experiment, students could research why pri mary standard solutions cannot be made directly using some solids. In the case of sodium hydroxide it i t is because it is difficult to obtain it pure. It is hygroscopic and reacts with carbon dioxide when exposed to the air, so a certain amount of both water and sodium carbonate is always present. If other cases, such as sodium carbonate-10-water, the salt is efflorescent. Students could then go on to research suitable solids for making primary standard solutions that can be used to standardise aqueous acids. The next task would be to research suitable solids to use as primary p rimary standards for standardising aqueous sodium hydroxide. If sulfamic acid is not available, then it can be substituted by another suitable solid acid, such as butanedioic acid (succinic acid), ethanedioic acid (oxalic acid) or even benzoic acid,



















7. The oxidation of propan-1-ol to produce propanal and propanoic acid

In preparation for this practical, students could be asked to research how to oxidise oxidi se propan-1-ol separately into propanal and propanoic acid, including how to identify the final product. Volunteers could then give a short presentation on each preparation, explaining the need for the varying conditions. The presentation could include, with reasons, any safety measures that need to be taken. There are many questions that can be asked about the practical procedure for the preparation of propanoic acid. For example, the need to use anti-bumping granules and why the water enters the bottom of the condenser and exists the top. Why does the mixture need to be refluxed? The students could then extend their research into the oxidation of secondary and tertiary alcohols. 8. Analysis of some inorganic and organic unknowns

In preparation for this practical, students could produce tabulated summaries of the tests for cations and anions (inorganic compounds), and for the functional groups they have so far studied (organic compounds).





















9a. Following the rate of the iodine-propanone reaction by a titrimetric method

The reaction between propanone and iodine in aqueous solution may be acid catalysed: I2(aq) + CH3COCH3(aq) + H+(aq) * CH3COCH2I(aq) + 2H+(aq) + I-(aq) The influence of the iodine on the reaction rate may be studied if the concentrations of propanone and acid protons effectively remain constant during the reaction. This is achieved by using a large excess of both acid and propanone in the original mixture. A single reaction mixture is made up and samples are withdrawn at regular reg ular time intervals, quenched and titrated against standard sodium thiosulfate. The titres are then plotted against the time of quenching of the sample. The results will show that the reaction i s zero



















10. Finding the activation energy of a reaction

In this activity students will calculate the activation energy of a reaction. Ther e are many places where they may slip up. The main ones are: 1.

The graph to be drawn needs to be ln t against 1/T, where T is in K. Check that

they are using the ‘ln’ ‘l n’ button on their calculator correctly.

2. They need to convert T from °C into K, and then work out 1/T. 3. A graph has to be plotted. Some may find the axes tricky if the numbers are very small or very large. 5. A line of best fit is then required. 6. The gradient of the line of best fit needs to be determined. The gradient is NOT the



















Further investigations could be based around the change in concentration of the



















14. The preparation of a transition metal complex

Two reliable preparations are: 1. 2.

[Cu(NH3)4SO4.H2O from aqueous ammonia and aqueous copper(II) sulfate. Fe(COO)2.2H2O from acidified iron(II) ammonium sulfate and ethanedioic acid.

In either case, the maximum possible mass of the complex can be calculated and then used to calculate the percentage yield. 15. Analysis of some inorganic and organic unknowns



















Research and referencing Students need to understand how scientific advances are communicated and reviewed. The process of peer-review, citations and attention to detail needed to present p resent scientific papers should be understood, as should the role of scientific journals, conferences and the international nature of research. Evidence revealed by research might 'support the idea that' but is not described as 'proving'. Objective scientific language is cautious and often conditional and this needs to be reflected in students' own practical recording.





















Independent thinking and evaluation



















Chemical analysis



















Addition of sodium hydroxide solution When dilute, aqueous sodium hydroxide is added to an aqueous solution of a metal ion a



















Addition of ammonia solution



















Silver nitrate solution for the presence of halide











































































































































Chemistry Teacher Practical Guide

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