Cambridge A Level Chemistry 9701 — 2012 Oct/Nov Paper 3 · Variant 3

READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Give details of the practical session and laboratory where appropriate, in the boxes provided. 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 fl uid. 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. Qualitative Analysis Notes are printed on pages 12 and 13. 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. CHEMISTRY 9701/33 Advanced Practical Skills 1 October/November 2012 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confi dential Instructions UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certifi cate of Education Advanced Subsidiary Level and Advanced Level This document consists of 13 printed pages and 3 blank pages and 1 insert. [Turn over IB12 11_9701_33/FP © UCLES 2012 *0926172746* Session Laboratory For Examiner’s Use 1 2 Total

2 9701/33/O/N/12 © UCLES 2012 For Examiner’s Use 1 You are to investigate how the rate of reaction between sodium thiosulfate and hydrochloric acid changes as the concentration of the sodium thiosulfate solution is varied. When aqueous sodium thiosulfate reacts with aqueous hydrogen ions present in an acid, a fi ne suspension of solid sulfur is formed in the solution. S2O3 2–(aq) + 2H+(aq) → S(s) + SO2(g) + H2O(l) The rate of reaction can be determined by measuring the time taken to produce a fi xed quantity of sulfur. The beaker containing a constant volume of reaction mixture is placed on the printed insert supplied. The time is recorded when the print is no longer visible through the suspension of sulfur. FA 1 is 0.150 mol dm–3 sodium thiosulfate, Na2S2O3. FA 2 is 0.500 mol dm–3 hydrochloric acid, HCl. distilled water Read through the instructions carefully and prepare a table for your results on page 4 before starting any practical work. In each of the following experiments you will use varying volumes of FA 1 and distilled water and a fi xed volume of FA 2. The total volume of solution used will be constant. (a) Method Experiment 1 ● Use the measuring cylinder labelled A to transfer 50 cm3 of FA 1 into a 250 cm3 beaker. ● Use the measuring cylinder labelled B to measure 20 cm3 of FA 2. ● Tip the FA 2 from measuring cylinder B into the beaker and immediately start timing. ● Stir the contents of the beaker once and place the beaker on the printed insert. ● View the print from directly above and through the solution in the beaker. ● Stop timing when the printed material on the insert is just no longer visible. ● Record the reaction time to the nearest second. ● Calculate and record the value of to 3 significant figures. ● Empty, rinse and dry the beaker. (1000) (reaction time)

3 9701/33/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use Experiment 2 ● Use the measuring cylinder labelled A to transfer 40 cm3 of FA 1 into the rinsed and dried beaker. ● Use the same measuring cylinder labelled A to transfer 10 cm3 of distilled water into the same beaker. ● Use the measuring cylinder labelled B to measure 20 cm3 of FA 2. ● Tip the FA 2 from measuring cylinder B into the beaker and immediately start timing. ● Stir the contents of the beaker once and place the beaker on the printed insert. ● View the print from directly above and through the solution in the beaker. ● Stop timing when the printed material on the insert is just no longer visible. ● Record the reaction time to the nearest second. ● Calculate and record the value of to 3 significant figures. ● Empty, rinse and dry the beaker. Experiments 3 – 5 ● Repeat the experiment using the following volumes of FA 1 and distilled water. Experiment 3 30 cm3 of FA 1 + 20 cm3 of distilled water Experiment 4 20 cm3 of FA 1 + 30 cm3 of distilled water Experiment 5 10 cm3 of FA 1 + 40 cm3 of distilled water Experiment 6 When you have completed experiments 1 – 5, carry out one further experiment using a different volume of both FA 1 and distilled water. When you have completed all of your experiments, empty and rinse the beaker. (1000) (reaction time)

4 9701/33/O/N/12 © UCLES 2012 For Examiner’s Use I II III IV V VI VII VIII IX X XI Record the results for all six experiments in the space below. Your table should include columns for the following. ● experiment number ● volume of FA 1 ● volume of distilled water ● reaction time ● [11] (b) The rate of reaction can be represented by the following formula. ‘rate’ = On the next page plot a graph of ‘rate’ against the volume of FA 1. Start each of the axes at zero. Draw the line of best fi t. (1000) (reaction time) (1000) (reaction time)

5 9701/33/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use I II III IV V [5]

6 9701/33/O/N/12 © UCLES 2012 For Examiner’s Use (c) A student carried out the experiments in a 100 cm3 beaker instead of a 250 cm3 beaker. State and explain what effect this would have on the times recorded. … … [2] (d) FA 1 is 0.150 mol dm–3 Na2S2O3. Calculate the initial concentration of Na2S2O3 in the reaction mixture in Experiment 5. Show your working. The initial concentration of Na2S2O3 in Experiment 5 = ………………………… mol dm–3 [2] (e) In your experiments, the volume of FA 1 represents the initial concentration of sodium thiosulfate in the reaction mixture. A text book states that the rate of reaction between aqueous sodium thiosulfate and hydrochloric acid is directly proportional to the concentration of sodium thiosulfate. Use your graph to decide whether the statement in the text book is correct or not. Explain your answer. … … … … [2]

7 9701/33/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use (f) When viewing the insert through the solution it is diffi cult to judge the exact moment when the printed material just disappears. This uncertainty is different for each experiment and is greater for longer reaction times when the printed material disappears slowly. Complete the table below, assuming the uncertainties given. Experiment 1 Experiment 5 recorded reaction time / s uncertainty / s ± 2 ± 8 percentage uncertainty % % [1] (g) Complete the headings in the table below to record the volume of FA 1 (aqueous sodium thiosulfate), the volume of distilled water and the volume of FA 2 (hydrochloric acid). In the second row copy the volumes used in Experiment 3 from your table of results on page 4. In the following two rows suggest volumes of each of the reagents that could be used in two further experiments, Experiment 7 and Experiment 8, to investigate how the rate of reaction varies with a change in the concentration of the acid. Do not carry out these experiments. Experiment 3 7 8 [2] [Total: 25]

8 9701/33/O/N/12 © UCLES 2012 For Examiner’s Use 2 Qualitative Analysis At each stage of any test you are to record details of the following. ● colour changes seen ● the formation of any precipitate ● the solubility of such precipitates in an excess of the reagent added Where gases are released they should be identifi ed by a test, described in the appropriate place in your observations. You should indicate clearly at what stage in a test a change occurs. Marks are not given for chemical equations. No additional tests for ions present should be attempted. If any solution is warmed, a boiling tube MUST be used. Rinse and reuse test-tubes and boiling tubes where possible. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. Solutions FA 3, FA 4, FA 5 and FA 6 each contain one cation and one anion from those listed on pages 12 and 13. (a) Some cations interfere with tests for anions and have to be removed from the solution before the tests for anions present can be performed. One way in which this can be carried out is to precipitate the cation in the form of its insoluble carbonate. Carry out the following tests on both FA 3 and FA 5. test observation FA 3 FA 5 To 5 cm depth of solution in a boiling tube, add all of the sodium carbonate, Na2CO3, from one of the tubes provided. Stir the mixture. Retain the mixture from FA 3 for use in (b). [4]

9 9701/33/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use (b) Filter the mixture from FA 3 from (a) into another boiling tube. Ignore any colour in the fi ltered solution. Add 5 cm depth of dilute nitric acid. This removes any excess of carbonate ions. Carry out the following tests on the acidifi ed fi ltrate from FA 3. test observation To 2 cm depth of the acidifi ed fi ltrate from FA 3 in a test-tube, add 1 cm depth of aqueous silver nitrate, then add an excess of aqueous ammonia. [1] (c) Carry out the following test on FA 4. test observation To 1 cm depth of FA 4 in a test-tube, add 1 cm depth of FA 3, then add a few drops of starch solution. [2]

10 9701/33/O/N/12 © UCLES 2012 For Examiner’s Use (d) Carry out the following tests. test observation FA 3 FA 4 FA 5 FA 6 To 1 cm depth of solution in a test-tube, use a dropping pipette to add, a little at a time, 0.5 cm depth of aqueous sodium hydroxide, then add a further 2 cm depth of aqueous sodium hydroxide. To 1 cm depth of solution in a test-tube, use a dropping pipette to add, a little at a time, 0.5 cm depth of aqueous ammonia, then add a further 2 cm depth of aqueous ammonia. [4] (e) The results from tests in (d) should enable you to identify either a single cation in a solution, or a pair of cations which have identical reactions with the reagents used. Identify any single ion that is present or suggest a pair of ions that may be present in each of the solutions. solution cation(s) FA 3 FA 4 FA 5 FA 6 [2]

11 9701/33/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use (f) Where you were unable to identify a single cation in (e), suggest a suitable reagent which would allow you to identify which cation is present in the solution. Do not carry out this test. The reagent to be used is … State the expected observations to identify the presence of each of the cations from the pair of ions you have given in (e). cation 1 … … cation 2 … … [1] (g) By considering the results of all your tests, enter one of the following responses in each of the boxes below. ● chloride ● bromide ● iodide ● no halide ion is present ● insufficient tests (have been performed to identify any halide ion) FA 3 FA 4 FA 5 [1] [Total 15]

12 9701/33/O/N/12 © UCLES 2012 Qualitative Analysis Notes Key: [ppt. = precipitate] 1 Reactions of aqueous cations ion reaction with NaOH(aq) NH3(aq) aluminium, Al 3+(aq) white ppt. soluble in excess white ppt. insoluble in excess ammonium, NH4 +(aq) no ppt. ammonia produced on heating – barium, Ba2+(aq) no ppt. (if reagents are pure) no ppt. calcium, Ca2+(aq) white ppt. with high [Ca2+(aq)] no ppt. chromium(III), Cr3+(aq) grey-green ppt. soluble in excess giving dark green solution grey-green ppt. insoluble in excess copper(II), Cu2+(aq) pale blue ppt. insoluble in excess blue ppt. soluble in excess giving dark blue solution iron(II), Fe2+(aq) green ppt. turning brown on contact with air insoluble in excess green ppt. turning brown on contact with air insoluble in excess iron(III), Fe3+(aq) red-brown ppt. insoluble in excess red-brown ppt. insoluble in excess lead(II), Pb2+(aq) white ppt. soluble in excess white ppt. insoluble in excess magnesium, Mg2+(aq) white ppt. insoluble in excess white ppt. insoluble in excess manganese(II), Mn2+(aq) off-white ppt. rapidly turning brown on contact with air insoluble in excess off-white ppt. rapidly turning brown on contact with air insoluble in excess zinc, Zn2+(aq) white ppt. soluble in excess white ppt. soluble in excess [Lead(II) ions can be distinguished from aluminium ions by the insolubility of lead(II) chloride.]

13 9701/33/O/N/12 © UCLES 2012 2 Reactions of anions ion reaction carbonate, CO3 2– CO2 liberated by dilute acids chromate(VI), CrO4 2–(aq) yellow solution turns orange with H+(aq); gives yellow ppt. with Ba2+(aq); gives bright yellow ppt. with Pb2+(aq) chloride, Cl –(aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)); gives white ppt. with Pb2+(aq) bromide, Br –(aq) gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq)); gives white ppt. with Pb2+(aq) iodide, I –(aq) gives yellow ppt. with Ag+(aq) (insoluble in NH3(aq)); gives yellow ppt. with Pb2+(aq) nitrate, NO3 –(aq) NH3 liberated on heating with OH–(aq) and Al foil nitrite, NO2 –(aq) NH3 liberated on heating with OH–(aq) and Al foil; NO liberated by dilute acids (colourless NO → (pale) brown NO2 in air) sulfate, SO4 2–(aq) gives white ppt. with Ba2+(aq) or with Pb2+(aq) (insoluble in excess dilute strong acids) sulfi te, SO3 2–(aq) SO2 liberated with dilute acids; gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids) 3 Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 gives a white ppt. with limewater (ppt. dissolves with excess CO2) chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 “pops” with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidifi ed aqueous potassium dichromate(VI) from orange to green

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16 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. 9701/33/O/N/12 © UCLES 2012 BLANK PAGE

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2012 series 9701 CHEMISTRY 9701/33 Paper 3 (Advanced Practical Skills 1), maximum raw mark 40 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 should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 2012 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

Page 2 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2012 9701 33 © Cambridge International Examinations 2012 Question Sections Indicative material Mark Total 1 (a) PDO Recording MMO Decisions PDO Display ACE Interpretation MMO Quality I All columns correctly headed and correct units given for all columns except for rate/(1000/time) e.g. /s, (s), time in s, time in seconds. II Records all times to the nearest second. Allow for only 5 expts carried out. III Additional experiment (experiment 6) uses volume of FA 1 [ 3 cm3 of any other, and adds water to make 50 cm3. Other volumes are those specified. IV Candidate gives all values of (1000/time) to 3 sig fig – ignore calculation or rounding errors (minimum of 4 expts carried out). V All values of (1000/time) correctly calculated to sig fig shown by candidate (minimum of 4 expts carried out). VI and Experiments 2 and 4: VII calculate 100(2t2 – t4)/t4 Y 20% for 1 mark; Y 10% for 2 marks. VIII and Experiments 3 and 5: IX calculate 100(3t3 – t5)/t5 Y 30% for 1 mark; Y 10% for 2 marks. X and Experiments 4 and 5: XI calculate 100(2t4 – t5)/t5 Y 30% for 1 mark; Y 10% for 2 marks. If the candidate has not completed the 5th experiment, marks VI and VII are available. Also check Experiments 1 and 2: t2 should equal to t1 × 5/4. Use the 10% and 20% boundaries. If only the first three experiments are completed, award Q marks based on Experiments 1 and 2 (as above). (If 50, 45, 40, 35, marks X and XI not available. Use 40 and 20 if there + ‘rescue’ pair as above.) The Examiner is to round all reaction times to the nearest second before awarding accuracy marks. (Volumes FA 1/expt no as specified in Qn) 1 1 1 1 1 6 [11]

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2012 9701 33 © Cambridge International Examinations 2012 (b) PDO Layout I Plots rate or (1000/time) on y-axis and volume of FA 1/FA 1 cm3 on x- axis. Axes correctly labelled. II Uniform scales selected. Each scale starts at zero and highest point plotted on each axis has used more than half of the available grid. III and Examiner to check all plotted points. IV Points must be correct to ½ small square and in correct small square. Award III and IV for correct points for all experiments carried out (minimum 5). Award III only if one mistake made. (If only four expts carried out then all 4 correct.) V Draws a “best-fit” straight line – one that passes close to the majority of points and points are balanced. The line does not have to pass through the origin. (Allow curve if appropriate.) 1 1 2 1 [5] (c) ACE Conclusions Depth (of solution) is greater, ... so time is shorter/less//time is faster//fewer seconds (time is conditional on depth) or solution/liquid depth unchanged so reaction time unchanged for 1 mark. 1 1 [2] (d) ACE Interpretation PDO Display Give one mark for a concentration of 0.021/0.0214/0.02143 mol dm–3 for expt 5. Working shown must include correct use of 70. 1 1 [2]

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2012 9701 33 © Cambridge International Examinations 2012 (e) ACE Interpretation Two pieces of evidence with no conclusion or one piece and conclusion. 2nd piece of evidence and conclusion. Evidence for ‘correct’ (i) a straight line/(line with) constant gradient (ii) straight line passes through origin (if appropriate from results) is 2 pieces of evidence (iii) line passes through origin = 1 if line drawn is straight Evidence for ‘incorrect’ (i) a curve has been drawn/no straight line/not constant gradient (ii) straight line does not pass through the origin (iii) points too scattered/not on best fit line (iv) a curve drawn but expect straight line = 2 A straight line, not passing through the origin could score both marks depending on explanation given (proportional but not directly proportional). If two points are compared they must be on or very close to the graph line. 1 1 [2] (f) ACE Interpretation Candidate correctly evaluates each % uncertainty. 1 [1] (g) ACE Improvement/ s Constant volume of FA 1. Varies volume of FA 2 and water correspondingly (Volume FA 2 + H2O same). 1 1 [2] Total 25

Page 5 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2012 9701 33 © Cambridge International Examinations 2012 FA 3 is CuCl2(aq); FA 4 is AlK(SO4)2(aq) + KI(aq); FA 5 is FeCl3(aq); FA 6 is Pb(NO3)2(aq) 2 (a) MMO Collection MMO Decisions Records a blue / greenish-blue ppt / solid with FA 3 and Na2CO3. Records a brown / rust / orange-brown / red-brown ppt / solid with FA 5 and Na2CO3. Records effervescence with FA 5 (or FA 3). Tests gas evolved with limewater. Allow from effervescence. 1 1 1 1 [4] (b) MMO Collection Records a white precipitate with silver nitrate solution and soluble in aqueous ammonia. 1 [1] (c) MMO Collection Records yellow-brown / orange-brown / brown / tan colour (solid/solution) (formed on mixing FA 4 and FA 3). Allow dark brown for solution only. Allow (qualified) brown solution with white / off-white / grey ppt. Dark / deep blue / blue-black / black / purple colour on adding starch solution 1 1 [2] (d) MMO Collection Mark the observations in the table horizontally or vertically to maximise marks available to the candidate. 4 [4] Observations Test FA 3 FA 4 FA 5 FA 6 NaOH(aq) blue ppt not dark/deep blue ppt white ppt (which dissolves as more added/then dissolves) red-brown / orange- brown / brown / rust ppt (not dark / deep brown) white ppt excess NaOH ppt insoluble (no change no observation provided ppt above) ppt soluble (if no ppt in 1st box allow no change) ppt insoluble (no change no observation provided ppt above) ppt soluble (not no change after ‘no ppt’) NH3(aq) blue ppt not dark/deep blue ppt white ppt red-brown / orange- brown / brown / rust ppt (not dark / deep brown) white ppt excess ammonia (ppt soluble) deep blue soln ppt insoluble (no change no observation provided ppt above) ppt insoluble (no change no observation provided ppt above) ppt insoluble (no change no observation provided ppt above)

Page 6 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2012 9701 33 © Cambridge International Examinations 2012 FA 3 is CuCl2(aq); FA 4 is AlK(SO4)2(aq) + KI(aq); FA 5 is FeCl3(aq); FA 6 is Pb(NO3)2(aq) (e) ACE Conclusions Con2 Con2 Give one mark for FA 3 Cu2+/copper/copper(II) and FA 5 Fe3+/iron(III). Give one mark for FA 4 and FA 6 Al3+/aluminium, Pb2+/lead Allow FA 4 Al3+(Pb2+) and FA 6 Al3+, Pb2+ (There must be some correct evidence for Cu2+ and Fe3+ in (d) but does not have to be fully correct.) 1 1 [2] (f) MMO Decisions De7 Selects appropriate reagent to distinguish between Al3+ and Pb2+ e.g. KI, K2CrO4, H2SO4, HCl (not BaCl2). 1 [1] (g) ACE Conclusions Con2 No error carried forward in this section. Award the mark for: FA 3 chloride FA 4 iodide FA 5 insufficient tests 1 [1] Total 15