Cambridge A Level Chemistry 9701 — 2011 Oct/Nov Paper 3 · Variant 6

This document consists of 11 printed pages and 1 blank page. DC (SJF) 52039/5 R © UCLES 2011 [Turn over * 6 1 4 5 4 7 5 7 5 0 * UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level 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 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. Qualitative Analysis Notes are printed on pages 11 and 12. 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 9701/36 Advanced Practical Skills 2 October/November 2011 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions Session Laboratory For Examiner’s Use 1 2 Total

2 9701/36/O/N/11 © UCLES 2011 For Examiner’s Use 1 Iodine and propanone react together at room temperature in the presence of an acid catalyst. CH3COCH3(aq) + I2(aq) CH3COCH2I(aq) + HI(aq) In the following experiment you will investigate how the rate of reaction alters when the concentration of a reagent is changed. When the reaction is complete, the solution turns colourless as all the iodine has been used up. It is possible to determine the rate of the reaction by measuring how long it takes for the mixture to go colourless. The product of the reaction, CH3COCH2I, is a strong irritant to the eyes. Make sure that at the end of each experiment you wash out the reaction flask with plenty of water. FB 1 is 2.0 mol dm–3 aqueous propanone, CH3COCH3. FB 2 is 3.0 mol dm–3 hydrochloric acid, HCl. FB 3 is 0.0050 mol dm–3 aqueous iodine, I2. (a) Method Read through the method and prepare a table for your results before starting any practical work. Experiment 1 • Fill the burette labelled FB 1 with the propanone solution, FB 1. • Fill the second burette with distilled water. • Run 20.0 cm3 of FB 1 into a 100 cm3 beaker. • Using a 25 cm3 measuring cylinder, add 20 cm3 of FB 2 to the beaker. • Using a second 25 cm3 measuring cylinder, measure 10 cm3 of FB 3. • Add the measured FB 3 to the solution in the 100 cm3 beaker and start timing immediately. • Stir the mixture once and place the beaker on a white tile. • Stop timing as soon as the solution goes colourless. Record this reaction time to the nearest second. • Wash out the beaker thoroughly. Experiment 2 • Run 14.0 cm3 of FB 1 into the 100 cm3 beaker. • Run 6.0 cm3 of distilled water into the 100 cm3 beaker. • Using the measuring cylinder, add 20 cm3 of FB 2 to the beaker. • Using the second measuring cylinder, measure 10 cm3 of FB 3. • Add the measured FB 3 to the solution in the 100 cm3 beaker and start timing immediately. • Stir the mixture once and place the beaker on a white tile. • Stop timing as soon as the solution goes colourless and record the reaction time as before. • Wash out the beaker thoroughly.

3 9701/36/O/N/11 © UCLES 2011 [Turn over For Examiner’s Use Experiment 3 Repeat the experiment as before using the volumes below. • 8.0 cm3 of FB 1 • 12.0 cm3 of distilled water • 20 cm3 of FB 2 • 10 cm3 of FB 3 Record all your results for experiments 1, 2 and 3 in the space below showing the volume of propanone solution, FB1, the volume of distilled water and the reaction time. [3] (b) Carry out two experiments to investigate further how the reaction time changes with different concentrations of propanone. Remember that the combined volume of propanone solution and distilled water must always be 20.0 cm3. Record these results in the space below. [2]

4 9701/36/O/N/11 © UCLES 2011 For Examiner’s Use (c) (i) Calculate the number of moles of iodine that were added in each experiment. ……………… mol (ii) Calculate the initial concentration of the iodine in 50 cm3 of the reaction mixture. initial concentration of iodine = ……………… mol dm–3 [2] (d) The rate of the reaction can be represented by the following formula. ‘rate’ = concentration of iodine from (c)(ii) reaction time × 105 Use your experimental results to complete the following table to include the reaction time and the ‘rate’. volume of propanone solution, FB1 / cm3 [2] (e) On the grid opposite, plot the ‘rate’ against the volume of propanone solution, FB1. Draw a line of best fit through the points you have plotted.

5 9701/36/O/N/11 © UCLES 2011 [Turn over For Examiner’s Use [8] I II III IV V VI VII VIII

6 9701/36/O/N/11 © UCLES 2011 For Examiner’s Use (f) (i) From your results what conclusion can you draw about the relationship between the rate of this reaction and the concentration of propanone? … … (ii) Suggest an improvement to the experiment that would allow you to be more confident about this conclusion. … … [3] (g) Carry out one additional experiment to investigate how the ‘rate’ is altered when the concentration of iodine is halved. Record the volume of each solution used and the reaction time in the space below. Calculate the ‘rate’ using the equation in (d). ‘rate’ = ……………… [2] (h) From your results in (d) and (g), what conclusion can you draw about the relationship between the rate of reaction and the concentration of iodine? … … [1] (i) In these experiments you used a burette to measure 20.0 cm3 of FB 1. Calculate the percentage error in measuring this volume. percentage error = ……………… [2] [Total: 25]

7 9701/36/O/N/11 © UCLES 2011 [Turn over For Examiner’s Use 2 Qualitative Analysis At each stage in 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 identified 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 full name or correct formula of the reagents must be given. FB 4, FB 5 and FB 6 are aqueous solutions each of which contains a single cation and a single anion. One of these solutions is a dilute acid and this is the only acid present. By carrying out specific tests you will identify all three compounds. (a) (i) Select a single chemical reagent which would allow you to identify the dilute acid. You may not use indicator paper. reagent ……………………………………… (ii) Use this reagent to test all three solutions and record your observations in an appropriate form in the space below. (iii) From your observations in (ii), identify which solution is the dilute acid. FB ……………………………………… is the dilute acid. [4]

8 9701/36/O/N/11 © UCLES 2011 For Examiner’s Use (b) The acid you have identified in (a)(iii) is dilute sulfuric acid. Complete the following table. test observations To 1 cm depth of FB 4 in a test-tube, add 1 cm depth of FB 5. To 1 cm depth of FB 5 in a test-tube, add 1 cm depth of FB 6. To 1 cm depth of FB 6 in a test-tube, add 1 cm depth of FB 4. [3] (c) Test the two remaining unidentified solutions separately with aqueous sodium hydroxide and aqueous ammonia. Record your observations in a suitable form below. You are reminded that if any solution is warmed a boiling tube MUST be used. [4]

9 9701/36/O/N/11 © UCLES 2011 [Turn over For Examiner’s Use (d) From your observations in (a), (b) and (c), identify the ions present in the two solutions tested in (c), giving the relevant evidence for each. If you have not been able to identify one or more of the ions, explain why the evidence obtained was insufficient. FB … cation … evidence … … … … anion … evidence … … … FB … cation … evidence … … … … anion … evidence … … … [4] [Total: 15]

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11 9701/36/O/N/11 © UCLES 2011 [Turn over Qualitative Analysis Notes Key: [ ppt. = precipitate ] 1 Reactions of aqueous cations ion reaction with NaOH(aq) NH3(aq) aluminium, Al3+(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.]

12 9701/36/O/N/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. 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) sulfite, 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, Cl2 bleaches damp litmus paper hydrogen, H2 “pops” with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium dichromate(VI) from orange to green

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2011 question paper for the guidance of teachers 9701 CHEMISTRY 9701/36 Paper 3 (Advanced Practical Skills 2), 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 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 October/November 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 AS/A LEVEL – October/November 2011 9701 36 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark 1 (a) PDO Layout Constructs a table for results to show volume FB 1, volume distilled water and time. 1 PDO Recording Correct headings and units. Units must have solidus: /s; brackets: (s); or describe in words: time in seconds or time in s. Units of volume: cm3 with solidus etc. as above. All recorded readings must have units. If units in headings they must not be repeated for each individual reading. 1 All times recorded to 1 second. Volumes of FB 1 and water to 1 or 0.05 cm3. 1 [3] (b) MMO Decision Two additional volumes of propanone chosen both of which are less than 20 cm3. These must not be more than one in the region 20–14, 14–8 and < 8 and not within 1 cm3 of the original values. 1 MMO Collection In both additional experiments water is added to make a total of 20 cm3. Some FB 1 must be used. 1 [2] (c) PDO Display (i) Working shown and answer = 5 × 10–5 mol. 1 (ii) Working shown and answer = (5 × 10–5) / 0.050 = 1 × 10–3 ecf from (i). 1 [2] (d) ACE Interpretation Calculates the rate correctly using ans (c) (ii) × 105/ time. Answers given to minimum 2 sig figs. 1 PDO Recording Units for rate given as mol dm–3s–1. 1 [2]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – October/November 2011 9701 36 © University of Cambridge International Examinations 2011 (e) PDO Layout I Rate on y-axis and volume on x-axis. Axes clearly labelled. 1 II Uniform scale chosen to use at least 6 large squares on y-axis and 4 on x-axis. This can include 0,0 if point plotted or line extrapolated. Ignore extrapolation > 20. 1 III Plotting of points. Points to be within ½ small square and in correct square. All recorded values should be plotted. 1 IV Draws a line of best fit. 1 MMO Quality Award V and VI for δ = ± 3 s 1 Award V only for δ= ± 6 s 1 Award VII and VIII for δ = ± 8 s 1 Award VII only for δ = ± 16 s 1 [8] (f) ACE Conclusion Notes linear relationship/(directly) proportional/ reaction is 1st order with respect to propanone. Rate increases as concentration (volume) increases would score one. 2 ACE Improvement Other volumes of iodine and repeat for varying volumes of propanone/repeat values for each run/carry out all experiments again/repeat any anomalous results/use burettes for FB 2 OR FB 3/ carry out relevant specified experiments/use a colorimeter/use starch to show colour change/ minimise intervals in volumes used. Do not allow: carry out more experiments/use other volumes of propanone/do experiments again/effects of changing conditions. 1 [3] (g) MMO Decision Uses 5 cm3 of iodine solution with extra 5 cm3 of distilled water. 1 ACE Interpretation Uses the expression (c) (ii)/2 and time from (g). Time must be different from that in (d). 1 [2] (h) ACE Conclusion Makes logical statement to compare rate with corresponding rate in (d). 1 [1]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – October/November 2011 9701 36 © University of Cambridge International Examinations 2011 (i) ACE Interpretation Uncertainty in each measurement is 0.05 cm3/0.1 cm3 is overall burette error. 1 0.10 × 100 = 0.50% 20.0 0.50 alone scores 2 0.05 × 100 = 0.25% scores 1 20.0 1 [2] [Total: 25] FB 4 is H2SO4; FB 5 is Pb(NO3)2; FB 6 is (NH4)2CO3 2 (a) MMO Decision (i) Named reagent involving CrO4 2– or CO3 2– solution/ Mg. Allow NaOH only if increase in T for FB 4 is used. 1 MMO Collection (ii) FB 4 gives orange solution/FB 4 gives effervescence/ / FB 4 gives effervescence Gas liberated not allowed unless test for gas given. 3 FB 5 gives yellow ppt/white ppt/no reaction/black ppt. FB 6 gives yellow solution/no reaction/no change. [4] (b) MMO Collection FB 4 + FB 5 and FB 5 + FB 6 white ppt. 1 FB 6 + FB 4 effervescence/bubbling. 1 Gas turns limewater milky/cloudy/chalky. 1 [3] (c) PDO Recording Presents information in a table to include both reagents and excess of each. Ignore anything described as the acid in (a). No additional reagents allowed. 1 FB 5 gives white ppt soluble in excess NaOH and white ppt insol in excess NH3(aq). 1 FB 6 gives no reaction with either NaOH or NH3(aq). 1 (Warms FB 6 + NaOH and tests) gas/ammonia turns damp red litmus blue. 1 FB 4 no change scores 1. [4]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – October/November 2011 9701 36 © University of Cambridge International Examinations 2011 (d) ACE Conclusions All conclusions must follow observations. For each unknown. One mark for ion and one mark for satisfactory evidence. FB 5 If CrO4 2– in (a), Pb2+ (1) 1 Evidence: yellow ppt and white ppt with NaOH or NH3 (1) 1 or if not CrO4 2– in (a) Al3+ or Pb2+ (both needed) (1) Evidence NH3 (ignore NaOH) (1) One of Al3+ or Pb2+ can score MP 2. FB 6 NH4 +/ CO3 2– (1) 1 Evidence: formation of NH3/CO2 from appropriate tests (1) 1 or FB 6 Ba2+ or NH4 + (both needed) (1) Evidence: no ppt both NaOH and NH3 (1) [4] [Total: 15]