Cambridge A Level Chemistry 9701 — 2015 Oct/Nov Paper 3 · Variant 6

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 an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fl uid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. 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 Paper 3 Advanced Practical Skills 2 October/November 2015 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confi dential Instructions Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level This document consists of 12 printed pages. [Turn over IB15 11_9701_36/3RP © UCLES 2015 *0597751623* Session Laboratory For Examiner’s Use 1 2 Total

2 9701/36/O/N/15 © UCLES 2015 1 You will investigate the rate of reaction between iron(III) ions, Fe3+, and iodide ions, I–. 2Fe3+(aq) + 2I–(aq) → 2Fe2+(aq) + I2(aq) The iodine, I2, produced can be reacted immediately with thiosulfate ions, S2O3 2–. I2(aq) + 2S2O3 2–(aq) → 2I–(aq) + S4O6 2–(aq) When all the thiosulfate has been used, the iodine produced will turn starch indicator blue-black. The rate of the reaction can therefore be measured by fi nding the time for the blue-black colour to appear. FB 1 is aqueous iron(III) chloride, FeCl 3. FB 2 is aqueous potassium iodide, KI. FB 3 is 0.0060 mol dm–3 sodium thiosulfate, Na2S2O3. starch indicator You are advised to read the instructions before starting any practical work and draw a table for your results in the space on page 3. (a) Method Experiment 1 ● Fill a burette with FB 1. ● Run 20.00 cm3 of FB 1 into a 100 cm3 beaker. ● Use the measuring cylinder to place the following in a second 100 cm3 beaker. ○ 10 cm3 of FB 2 ○ 20 cm3 of FB 3 ○ 10 cm3 of starch indicator ● Add the contents of the second beaker to the first beaker and start timing. ● Stir the mixture once and place the beaker on the white tile. ● The mixture turns brown and then yellow before turning a blue-black colour. Stop timing when this blue-black colour appears. ● Record in your table the volume of FB 1 used, the volume of distilled water used and the time to the nearest second for the blue-black colour to appear. ● Wash both beakers. For each of Experiments 2-6 you should complete your results table to show the volume of FB 1 used, the volume of distilled water used and the time taken to the nearest second for the blue-black colour to appear. Experiment 2 ● Fill the other burette with distilled water. ● Run 10.00 cm3 of FB 1 into a 100 cm3 beaker. ● Run 10.00 cm3 of distilled water into the same beaker. ● Use the measuring cylinder to place the following in a second 100 cm3 beaker. ○ 10 cm3 of FB 2 ○ 20 cm3 of FB 3 ○ 10 cm3 of starch indicator ● Add the contents of the second beaker to the first beaker and start timing. ● Stir the mixture once and place the beaker on the white tile. ● Stop timing when a blue-black colour appears. ● Wash both beakers.

3 9701/36/O/N/15 © UCLES 2015 [Turn over I II III IV V VI VII VIII Experiments 3-6 Carry out four further experiments to investigate the effect of changing the concentration of Fe3+(aq) by altering the volume of aqueous FeCl 3, FB 1, used. You should not use a volume of FB 1 that is less than 6.00 cm3 and the total volume of the reaction mixture must always be 60 cm3. [8]

4 9701/36/O/N/15 © UCLES 2015 (b) Calculations The rate of reaction can be found by calculating the change in concentration of Fe3+(aq) that occurred when enough iodine was produced to change the colour of the indicator to blue-black. Use your data and the equations on page 2 to carry out the following calculations. Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Calculate the number of moles of thiosulfate ions, S2O3 2– used in each experiment in (a). moles S2O3 2– = … mol (ii) Calculate the number of moles of iodine, I2, that react with the number of moles of S2O3 2– in (i). moles I2 = … mol (iii) Calculate the number of moles of iron(III) ions, Fe3+, that were used to produce the number of moles of iodine in (ii). moles Fe3+ = … mol (iv) When the moles of Fe3+ that you calculated in (iii) reacted, a change in the concentration of moles of Fe3+ occurred. Calculate this change in concentration. change in concentration of Fe3+(aq) = … mol dm–3 (v) The following formula can be used as a measure of the ‘rate of reaction’. ‘rate of reaction’ = change in concentration of Fe3+(aq) reaction time × 106 Complete the table to show the volume of FB 1, the reaction time and the rate in Experiments 1-6. You should include units. If you were unable to calculate a value for the change in concentration of Fe3+(aq) in (iv), you should assume it is 2.50 × 10–3 mol dm–3. (Note: this is not the correct value.) Experiment 1 2 3 4 5 6 [5]

5 9701/36/O/N/15 © UCLES 2015 [Turn over (c) On the grid, plot the rate (y-axis) against the volume of FB 1 (x-axis). Draw a line of best fi t through the points. You should identify any points you consider anomalous. [4]

6 9701/36/O/N/15 © UCLES 2015 (d) Using your graph, what conclusion can you reach about the effect of changing the concentration of FeCl 3 on the rate of the reaction between Fe3+(aq) and I–(aq)? … … … [2] (e) A student wanted to investigate how changing the concentration of I– would affect the rate of reaction. Explain how this investigation could be carried out. … … … … [2] (f) It was found, by carrying out experiments similar to those used in (a), that increasing the concentration of I– increased the rate of the reaction. The student suggested modifi cations to the method as used in (a). In each case, state what the effect would be on the reaction time in Experiment 1 and explain how these changes would affect the possible errors in the measurements. Suggested modifi cation 1 The reaction was carried out using the same volumes of all reagents but with the concentrations of FB 1 and FB 2 being double their original values. … … … Suggested modifi cation 2 The reaction was carried out using half the volume of all reagents. … … … [4]

7 9701/36/O/N/15 © UCLES 2015 [Turn over (g) (i) Which of the experiments you carried out in (a) had the greatest percentage error in the reaction time? … (ii) Calculate this percentage error. Assume that the error in measuring the reaction time is ±0.5 s. percentage error = … % [2] [Total: 27]

8 9701/36/O/N/15 © UCLES 2015 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. Half fi ll the 250 cm3 beaker with water and heat it to about 80 °C and then switch off the burner. This will be used as a water bath in (b). Keep two clean, dry test-tubes for use in (b). (a) FB 4 and FB 5 each contain two cations and one anion. One of the cations in FB 4 is the same as one of the cations in FB 5. The anion in FB 4 is the same as the anion in FB 5. (i) Separately dissolve about half of each of your samples of FB 4 and FB 5 in about 5 cm depth of distilled water in a boiling tube. Carry out the following tests and record your observations in the table. test observations FB 4 FB 5 To a 1 cm depth of solution in a test-tube, add a 1 cm depth of aqueous edta. To a 1 cm depth of solution in a test-tube, add a 1 cm depth of aqueous potassium iodide.

9 9701/36/O/N/15 © UCLES 2015 [Turn over test observations FB 4 FB 5 To a 1 cm depth of solution in a test-tube, add aqueous sodium hydroxide. To a 1 cm depth of solution in a test-tube, add aqueous ammonia. To a 1 cm depth of solution in a test-tube, add a 1 cm depth of aqueous barium chloride or aqueous barium nitrate, then add dilute hydrochloric acid. (ii) From the observations identify three of the ions present in FB 4 and FB 5. The anion present in both FB 4 and FB 5 is … . One cation present in FB 4 is … . One cation present in FB 5 is … . (iii) FB 4 and FB 5 each contain another cation from the list on page 11. This cation is the same in both FB 4 and FB 5. Carry out a test to identify this cation. Record details of the test and your observations. … … … Identify the cation present in both FB 4 and FB 5. Cation is … . [8]

10 9701/36/O/N/15 © UCLES 2015 (b) FB 6 is an aqueous solution of an organic compound. (i) Complete the table below. The observation with 2,4-dinitrophenylhydrazine has already been made. test observations To a 1 cm depth of FB 6 in a test-tube, a few drops of 2,4-dinitrophenylhydrazine were added. orange precipitate formed To a 1 cm depth of FB 6 in a test-tube, add a 2 cm depth of dilute sulfuric acid. Place the test-tube in the water bath. Then add two or three drops of acidifi ed aqueous potassium manganate(VII). To a 1 cm depth of aqueous silver nitrate in a test-tube, add a few drops of aqueous sodium hydroxide. Then add aqueous ammonia until the brown precipitate just dissolves. To this, add a 1 cm depth of FB 6. Place the test-tube in the water bath and leave to stand. Care: rinse the tube as soon as you have completed this test. (ii) What conclusion can you make about the identity of FB 6 from the observation of its reaction with 2,4-dinitrophenylhydrazine? … (iii) What conclusion can you make about the identity of FB 6 from the observation of its reactions with acidifi ed potassium manganate(VII) and silver nitrate in ammonia solution? … (iv) What change in the oxidation state of silver occurs in the reaction between FB 6 and silver nitrate in ammonia solution? change from … to … [5] [Total: 13]

11 9701/36/O/N/15 © UCLES 2015 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 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

12 9701/36/O/N/15 © UCLES 2015 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. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. 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 chloride, Cl –(aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)) bromide, Br –(aq) gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq)) iodide, I –(aq) gives yellow ppt. with Ag+(aq) (insoluble in NH3(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) (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 manganate(VII) from purple to colourless

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 2015 series 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 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 2015 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9701 36 © Cambridge International Examinations 2015 Question Indicative material Mark Total 1 (a) I Constructs a single table for 6 results. II Correct headings and units. Volumes / V/vol in cm3 or / cm3 or (cm3), time / t in seconds or / s or (s). III All times recorded to the nearest second and all volumes to 0.05 cm3. IV Four further experiments chosen with intervals not less than 2 cm3 and no volume less than 6 cm3. At least one volume must be less than 10 cm3 and at least one must be more than 10 cm3. V Water added to make total volume of FB 1 and water 20 cm3 in each experiment and no other changes in volume. VI Times increase with decrease in volume FB 1. VII and VIII Examiner rounds times to nearest second and calculates (time for expt 2) /( time for expt 1) to 2 dp. Ratio is compared with that of Supervisor. Award marks as follows: VI if ratio within 0.2 of Supervisor. VII if ratio within 0.1 of Supervisor. 1 1 1 1 1 1 1 1 [8] (b) (i) number of moles S2O3 2− = 1.2 × 10 −4 (ii) Correctly calculates answer to (i) / 2 = 0.6 × 10 −4 and (iii) answer to (ii) × 2 = 1.2 × 10−4. (iv) Correct expression 0.06 10 1.2 4 − × = 2.(0) × 10−3 (v) Rates correctly calculated using t 10 6 × (c)(iv) Units for rate given as mol dm−3 s−1 and 3 correct columns used. 1 1 1 1 1 [5] (c) I Axes labelled – rate on y-axis and volume or FB 1 / cm3 on x-axis II Uniform scales to use at least half of each axis including 0,0 if point plotted. III Correct plotting – all points recorded plotted and within half a small square and within correct small square. 1 1 1

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9701 36 © Cambridge International Examinations 2015 IV Draws a line of best fit. (can be straight line or curve). Straight lines must be straight (single line with no kinks, drawn using a ruler) or a smooth curve (gradual change in gradient). Points not on the line must be balanced on either side of the best fit line but any points ringed or labelled as anomalous should be ignored. 1 [4] (d) Rate increases as concentration of Fe3+ increases Comment on graph as drawn. Possible comments include: The results are consistent since all points are on / near the line. An anomalous point is present / or not present. Would have expected graph to go through 0,0. Straight line shows rate proportional to conc / vol 1 1 [2] (e) Alter volume of FB 2 / KI whilst keeping other volume of FB 1 / FeCl3 constant Add water to keep total volume constant 1 1 [2] (f) Modification 1 Reaction time less. (Less accurate since) larger % error (in time). Modification 2 Reaction time stays the same (Less accurate since) greater % error in volume. 1 1 1 1 [4] (g) (i) Experiment with shortest reaction time (ii) Correct expression time reaction smallest 100% 0.5 × 1 1 [2] [Total: 27]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9701 36 © Cambridge International Examinations 2015 FB 4 Cu(NH4)2(SO4)2.6H2O, FB 5 Fe(NH4)(SO4)2.6H2O, FB 6 C6H12O6 2 (a) (i) FB 4 FB 5 colour to dark(er) / deep blue no change / no reaction. brown (solution) (+ off-white / beige ppt) no reaction / no change / no ppt blue ppt. insol. in excess green ppt. insol in excess / goes brown blue ppt. soluble in excess to give dark blue solution green ppt. insol in excess / goes brown white ppt. and insol in HCl / no change white ppt and insol in HCl / no change 1 1 1 1 1 [5] (ii) Anion present in both is SO4 2−/ sulfate and FB 4 Cu2+ / copper(II) and FB 5 Fe2+/iron(II) 1 [1] (iii) Heat with (aqueous) sodium hydroxide. Ammonia / gas given off that turns litmus blue Cation is NH4 + / ammonium 1 1 [2] (b) (i) Manganate (VII) changes from purple to colourless. Silver colour / grey ppt / black ppt / silver mirror 1 1 [2] (ii) Aldehyde and / or ketone (both needed) / carbonyl compound / functional group is C=O. 1 [1] (iii) Aldehyde 1 [1] (iv) +1 to 0 1 [1] [Total: 13]