Cambridge A Level Chemistry 9701 — 2011 May/June Paper 5 · Variant 3

This document consists of 9 printed pages and 3 blank pages. DC (NF/DJ) 41305 © UCLES 2011 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Level READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. You may lose marks if you do not show your working or if you do not use appropriate units. Use of a Data Booklet is unnecessary. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. * 5 7 5 2 0 0 1 3 1 1 * CHEMISTRY 9701/53 Paper 5 Planning, Analysis and Evaluation May/June 2011 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. For Examiner’s Use 1 2 Total

2 © UCLES 2011 9701/53/M/J/11 For Examiner’s Use 1 Reactions involving two aqueous solutions are dependent on collisions occurring between the particles of the two reagents. As the temperature of the system is raised, the average kinetic energy of the particles increases. You are to plan an experiment to investigate how the rate of the reaction between hydrochloric acid and sodium thiosulfate, Na2S2O3, depends on the temperature of the reaction. When these two reagents react, after a short period they slowly produce a white or yellow precipitate of sulfur. As more sulfur is produced, the reaction mixture becomes more cloudy until it cannot be seen through (i.e. it is opaque). The time taken for the mixture to become opaque can be dependent on the relative concentrations of the reagents or the temperature of the reaction mixture. (a) (i) Predict how the rate of reaction will change if the temperature of the reagents is increased. Using the idea of how the kinetic energy of the particles changes as the temperature of the reagents increases, explain your prediction in terms of particle collisions. prediction … … … explanation … … … … (ii) Display your prediction in the form of a sketch graph, clearly labelling the axes. 0 [3]

3 © UCLES 2011 [Turn over 9701/53/M/J/11 For Examiner’s Use (b) In the experiment you are about to plan, identify the following. (i) the independent variable … (ii) the dependent variable … [2] (c) Draw a diagram of the apparatus and experimental set up you would use to carry out this experiment. Your apparatus should use only standard items found in a school or college laboratory and show clearly the following. (i) the apparatus used as the reaction vessel and how the thermometer will be positioned in order to measure the temperature of the solution as accurately as possible (ii) how the solution will be heated Label each piece of apparatus used, indicating its size or capacity and the temperature range that the thermometer should cover. [2]

4 © UCLES 2011 9701/53/M/J/11 For Examiner’s Use (d) Using the apparatus shown in (c) design a laboratory experiment to test your prediction in (a). In addition to the standard apparatus present in a laboratory you are provided with the following materials, 0.100 mol dm–3 aqueous sodium thiosulfate, 1.00 mol dm–3 hydrochloric acid, A stop-watch/clock with second hand. Give a step-by-step description of how you would carry out the experiment by stating (i) the number of experiments you would do, and their temperature range (minimum and maximum temperatures), (ii) what you would keep constant in all the experiments, (iii) what temperature measurements you would make, (iv) how you would use the cloudiness (opacity) of the reaction mixture to measure the time taken for each reaction. … … … … … … … … … … … … … … … … … … … [5]

5 © UCLES 2011 [Turn over 9701/53/M/J/11 For Examiner’s Use (e) State a hazard that must be considered when planning the experiment and describe precautions that should be taken to keep risks to a minimum. … … [1] (f) Draw a table with appropriate headings to show the data you would record when carrying out your experiments and the values you would calculate in order to construct a graph to support or reject your prediction in section (a). The headings must include the appropriate units. [2] [Total: 15]

6 © UCLES 2011 9701/53/M/J/11 For Examiner’s Use 2 The solubility of potassium chlorate(V) in water increases with temperature. The units of solubility are grams per one hundred grams of water (g / 100g water). An experiment is carried out to investigate this solubility. • An empty boiling tube was weighed and the mass recorded. • Some distilled water was added to the boiling tube and the new mass recorded. • A small sample of potassium chlorate(V) was added and this new mass recorded. • The boiling tube was carefully heated with stirring until all the solid had dissolved. • The apparatus was allowed to cool slowly while constantly stirring and the temperature recorded when the first crystals appeared in the tube. (a) The results of several such experiments are recorded below. A B C D E F G crystallising temperature / °C mass of boiling tube / g mass of boiling tube and water / g mass of boiling tube, water and solid / g 20.0 10.10 35.10 36.85 25.0 10.20 35.20 37.45 30.0 9.80 29.20 31.20 40.0 9.95 32.95 36.55 45.0 10.35 30.35 33.45 50.0 9.90 34.90 39.40 60.0 9.70 30.70 35.53 65.0 9.95 33.95 40.07 70.0 10.45 30.45 36.15 75.0 10.35 35.35 42.75 80.0 10.05 35.05 44.05 90.0 10.10 40.10 53.90 Process the results in the table to calculate the solubility in g / 100 g of the potassium chlorate(V) for each of the temperatures listed. Record these values to two decimal places in the additional columns of the table. You may use some or all of the columns. Label the columns you use. For each column you use include units where appropriate and an expression to show how your values are calculated. Use the column headings A to G for these expressions (e.g. A–B). [3]

7 9701/53/M/J/11 © UCLES 2011 [Turn over (b) Plot a graph to show the variation of solubility with temperature. Draw the line of best fit. [4]

8 © UCLES 2011 9701/53/M/J/11 For Examiner’s Use (c) Circle and label on the graph any point(s) you consider anomalous. For each anomalous point give a different reason why it is anomalous clearly indicating which point you are describing. … … … … … … … … [4] (d) A solution of potassium chlorate(V) is made up using 50 g of water. This is found to be saturated at 85 °C. The solution is then cooled to 35 °C. Using your graph calculate the mass of solid deposited as a result of this temperature change. [2]

9 © UCLES 2011 9701/53/M/J/11 For Examiner’s Use (e) From the pattern of solubility demonstrated by your graph predict and explain whether the dissolving of potassium chlorate(V) in water is an exothermic or an endothermic reaction. prediction … … … … explanation … … … … … … [2] [Total: 15]

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12 9701/53/M/J/11 © UCLES 2011 Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. BLANK PAGE

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Level MARK SCHEME for the May/June 2011 question paper for the guidance of teachers 9701 CHEMISTRY 9701/53 Paper 5 (Planning, Analysis and Evaluation), maximum raw mark 30 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes must be read in conjunction with the question papers and the report on the examination. • Cambridge will not enter into discussions or correspondence in connection with these mark schemes. Cambridge is publishing the mark schemes for the May/June 2011 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme: Teachers’ version Syllabus Paper GCE A LEVEL – May/June 2011 9701 53 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark 1 (a) PLAN Problem Predicts that rate of reaction will be proportional to the temperature/ increasing temperature increases rate Greater frequency/greater chance/greater/energy of collision/more particles have energy greater than the activation energy/more effective collisions/more often. Any graph showing an increasing rate with temperature (curve or straight line) Line may start anywhere. Ignore units but axes must be labelled and can be ‘either way round’. Use of ‘time’ negates (If time is mentioned in the prediction the graph might be worth a mark as an ECF, the prediction of course would be worth zero) Allow a consequential answer from an incorrect prediction. [1] [1] [1] (b) PLAN Problem (i) Temperature as the independent variable (ii) Time identified as dependent variable/rate (of reaction). Other incorrect suggestions negate in either part. [1] [1] (c) PLAN Methods (i) A ‘container’ with liquid and an immersed thermometer being heated. No mark if sealed. (If the candidate chooses at this stage to set up an experiment using a water-bath [which is of course the way many of us would carry out this exercise] with the thermometer immersed in the bath and reaction vessel(s) shown we should give this mark here. However, in (d) in order to access the ‘temperature’ mark using such a water-bath ‘equilibration’ must be stated or clearly implied.) (ii) Volume of ‘container’ (any conical flask or beaker must have a volume of at least 20 cm3) and thermometer range (to cover the candidate’s expts.) (Upper and lower temps on the thermometer to be given). Allow a boiling/test tube without a volume. [1] [1] (d) PLAN Methods (i) At least 5 experiments (not repeats of the same expt.) To cover at least a 25 oC range (no greater than 100 oC) (ii) Maintaining the volumes of both reagents (not total vol.) If a candidate states that the experiment should be repeated, (even if it is the same experiment) in the absence of any contrary detail, give this mark. (iii) Temperature(s) of both reagents taken/or temperature taken immediately after mixing. (see note above) [1] [1] [1] [1]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE A LEVEL – May/June 2011 9701 53 © University of Cambridge International Examinations 2011 (iv) Statement of timing to (first) opacity/determination of the point of opacity (e.g. the disappearing cross). [If it is clear that the timing starts after mixing and heating has taken place do not award this mark]. Some of these points ((i), (ii) and (iii))may be available from the table. These first three marks can also be awarded even if the candidate is clearly bent on carrying out a different experiment. E.g. an experiment which involves an apparent rise of temperature during the experiment or one which seems to be measuring the time between the first opacity and a ‘final’ opacity. [1] (e) PLAN Methods Reference to ‘hot’ apparatus/sulfur dioxide evolved/hydrochloric acid (ignore any reference to possible effects) with ‘use of heat proof gloves/use of tongs’/use of fume cupboard/gloves and goggles. Ignore spillages [1] (f) PLAN Methods There are four items to be covered here table to include; Temperature; (If candidates record two temperatures per experiment and this is as a result of a ‘flawed experimental design’ allow the temperature mark even if a ∆t is also given. However ∆t alone does not gain the mark.) Time to opacity (ignore start times); Rate (allow 1/t or 1/time); All with correct units. Allow /s or seconds, (s or seconds). Allow /s–1 or seconds–1, (1/s or 1/seconds) Ignore all other columns All four correct 2 marks; Any error 1 mark; Two or more errors zero. If one column missing but others fully correct allow one mark [2] Total [15]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE A LEVEL – May/June 2011 9701 53 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark 2 (a) ACE Data Focus on the solubility column initially then: Correct heading and formula, Correct units,(allow g/100g without the solidus) All calculations correct (allow one calculation or sf error). (No ecf from earlier errors) (no ecf in solubility calc) Give one mark for; two fully correct headings including units/two correct columns/one heading with units and one column correctly calculated ( any combination) (allow one error) [1] [1] [1] (b) ACE Data Unambiguously labelled axes (ignore units) (Solubility must be on the y-axis) If either mass is plotted against temperature all the three subsequent marks are available but not this first mark. But, see below. Appropriate scaling (axes to allow points to cover at least half of the grid in each direction). Check points 1,5, 7 and 12. Points need to be plotted in the correct small square unless the points should be on a line or at a corner (then it has to be there).If the point is on a grid line and should not be it is incorrect. Line of best fit (the correct graph is a curve, hence straight lines gain zero. If however a wrong set of results genuinely produces a straight-line, award the mark for a straight-line) (ignore extrapolation at temperatures lower than 20 oC) Examiner judgement for best-fit curves. [1] [1] [1] [1] (c) ACE Evaluation One identified anomaly At least one more anomaly identified (max 6 anomalies) (must include the most anomalous)(any anomaly on the line negates) Correct explanation for the anomaly. If either or both of the anomalies are mentioned here but not ‘ringed’ on the graph allow the marks. Correct explanation for the second anomaly Anomalies above the line: temperature read too late/super cooling Below the line: water lost (due to evaporation) (so crystals form at a higher temp.)/temperature read before crystallisation. ONE mark for two correct reasons which are not tied to a particular point. Ignore any reference that might be ‘human error’ e.g. reference to spillage, mass loss, misreading of the balance or thermometer etc. These last two marks are not available if the graph includes a mass and no further marks are available in (d) or (e) [1] [1] [1] [1]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE A LEVEL – May/June 2011 9701 53 © University of Cambridge International Examinations 2011 (d) ACE Data ACE Conclusions Takes readings from the graph at 85 oC and 35 oC Calculates the mass of solid (divides by 2 and subtracts or the reverse). Correct answer alone gets both marks. [1] [1] (e) ACE Conclusions For stating ‘endothermic’. For the statement ‘solubility increases with temperature’ (Allow alternatives for both marks if the graph supports e.g. exothermic if the graph slopes the other way and solubility decreasing with temperature etc.) [1] [1] Total [15]