Cambridge A Level Chemistry 9701 — 2015 May/June Paper 3 · Variant 5

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 14 and 15. 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 9701/35 Paper 3 Advanced Practical Skills 1 May/June 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 13 printed pages and 3 blank pages. [Turn over IB15 06_9701_35/5RP © UCLES 2015 *7333871663* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/35/M/J/15 © UCLES 2015 I II III IV V VI VII 1 In this experiment you will determine the formula of iron(III) ammonium sulfate, FeNH4(SO4)2.xH2O, where x is the number of molecules of water of crystallisation. A known mass of this iron(III) compound reacted with excess acidifi ed potassium iodide to produce iodine. You will determine the amount of iodine produced by titrating the mixture with sodium thiosulfate. FA 1 is 0.900 mol dm–3 sodium thiosulfate, Na2S2O3. FA 2 is a solution of iodine, I2, produced as outlined in the paragraph above. starch indicator (a) Method Diluting FA 1 • Pipette 25.0 cm3 of FA 1 into the 250 cm3 volumetric (graduated) flask. • Make the solution up to the mark using distilled water. • Shake the flask to mix the solution thoroughly before using it for your titrations. • Label this diluted solution of sodium thiosulfate FA 3. • Rinse the pipette with distilled water. Keep FA 1 for use in Question 3. Titration • Fill the burette with FA 3. • Use the pipette to transfer 25.0 cm3 of FA 2 into a conical flask. • Add FA 3 from the burette into the conical flask until the mixture becomes pale yellow. • Then add 10 drops of starch indicator to give a blue-black colour. • Continue adding FA 3 until this blue-black colour disappears. This is the end-point of the titration. • Perform a rough titration and record your burette readings in the space below. The rough titre is … cm3. • Carry out as many accurate titrations as you think necessary to obtain consistent results. • Make sure any recorded results show the precision of your practical work. • Record in a suitable table below, all of your burette readings and the volume of FA 3 added in each accurate titration. [7]

3 9701/35/M/J/15 © UCLES 2015 [Turn over (b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FA 2 required … cm3 of FA 3. [1] (c) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Using information on page 2, calculate the concentration, in mol dm–3, of sodium thiosulfate in FA 3. concentration of Na2S2O3 in FA 3 = … mol dm–3 (ii) Calculate the number of moles of sodium thiosulfate present in the volume of FA 3 calculated in (b). moles of Na2S2O3 = … mol (iii) Use the equation below to calculate the number of moles of iodine that reacted with the sodium thiosulfate in (ii). I2 + 2Na2S2O3 → 2NaI + Na2S4O6 moles of I2 = … mol (iv) Calculate the concentration of I2, in mol dm–3, in FA 2. concentration of I2 = … mol dm–3

4 9701/35/M/J/15 © UCLES 2015 (v) The iodine in FA 2 was produced by the reaction of iron(III) ions with excess potassium iodide. Balance the equation for this reaction. … Fe3+(aq) + … I–(aq) → … Fe2+(aq) + … I2(aq) Use your answer to (iv) and this equation to calculate the number of moles of iron(III) ions that reacted to produce the iodine in 1.00 dm3 of FA 2. moles of Fe3+ = … mol (vi) The formula of the iron(III) compound is FeNH4(SO4)2.xH2O. 38.56 g of this compound was weighed out and added to excess aqueous acidifi ed potassium iodide. FA 2 was made by making the resulting solution of iodine up to 1.00 dm3 with distilled water. Use this information and your answer to (v) to calculate the number of moles of water of crystallisation, x, in one mole of the iron(III) compound. [Ar: H, 1.0; N, 14.0; O, 16.0; S, 32.1; Fe, 55.8] x = … [6] [Total: 14]

5 9701/35/M/J/15 © UCLES 2015 [Turn over 2 In this experiment you will determine the enthalpy change, ∆H, for the reaction of zinc with iron(II) sulfate. Zn(s) + FeSO4(aq) → Fe(s) + ZnSO4(aq) In order to do this, you will determine the enthalpy changes for the reactions of zinc and iron with aqueous copper(II) sulfate. Excess of the two metals will be used during the determinations. Then you will use Hess’ Law to calculate the enthalpy change for the reaction above. FA 4 is zinc, Zn. FA 5 is iron, Fe. FA 6 is 0.500 mol dm–3 copper(II) sulfate, CuSO4. (a) Determination of the enthalpy change for the reaction of zinc, FA 4, with aqueous copper(II) sulfate, FA 6. Method • Support a plastic cup inside the 250 cm3 beaker. • Use the measuring cylinder to transfer 25 cm3 of FA 6 into the plastic cup. • Measure and record the initial temperature of the solution in the space below. • Add all the FA 4 from the container to the FA 6 in the plastic cup. • Stir constantly until the maximum temperature is reached. • Measure and record the maximum temperature. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. • Calculate and record the temperature rise. [3]

6 9701/35/M/J/15 © UCLES 2015 (b) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm3 of solution by 1.0 °C.] energy produced = … J (ii) Calculate the number of moles of copper(II) sulfate in 25 cm3 of FA 6. moles of CuSO4 = … mol (iii) Calculate the enthalpy change, in kJ mol–1, for the reaction below. Zn(s) + CuSO4(aq) → Cu(s) + ZnSO4(aq) enthalpy change = … … kJ mol–1 sign value [2]

7 9701/35/M/J/15 © UCLES 2015 [Turn over (c) Determination of the enthalpy change for the reaction of iron, FA 5, with aqueous copper(II) sulfate, FA 6. Method • Support the second plastic cup inside the beaker. • Use the measuring cylinder to transfer 25 cm3 of FA 6 into the plastic cup. • Measure and record the initial temperature of the solution in the space below. • Add all the FA 5 from the container to the FA 6 in the plastic cup. • Stir constantly until the maximum temperature is reached. • Measure and record the maximum temperature. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. • Calculate and record the temperature rise. Keep solution FA 6 for use in Question 3. [2] (d) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm3 of solution by 1.0 °C.] energy produced = … J (ii) Calculate the enthalpy change, in kJ mol–1, for the reaction below. Fe(s) + CuSO4(aq) → Cu(s) + FeSO4(aq) enthalpy change = … … kJ mol–1 sign value [2]

8 9701/35/M/J/15 © UCLES 2015 (e) Use your values for the enthalpy changes calculated in (b)(iii) and (d)(ii) to calculate the enthalpy change for the reaction below. Zn(s) + FeSO4(aq) → Fe(s) + ZnSO4(aq) Show clearly how you obtained your answer by drawing a Hess’ Law energy cycle. (If you were unable to calculate the enthalpy changes, assume that the value in (b)(iii) is –210 kJ mol–1 and the value in (d)(ii) is –144 kJ mol–1. Note: these are not the correct values.) enthalpy change = … … kJ mol–1 sign value [2] (f) (i) Calculate the maximum percentage error in the temperature rise in (c). percentage error = … % (ii) Apart from using a more accurately calibrated thermometer, suggest one improvement that could be made to this experiment that would increase the accuracy. … … … [2] [Total: 13]

9 9701/35/M/J/15 © UCLES 2015 [Turn over 3 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. 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.

10 9701/35/M/J/15 © UCLES 2015 (a) FA 1, used in Question 1, is an aqueous solution of sodium thiosulfate. FA 6, used in Question 2, is an aqueous solution of copper(II) sulfate. FA 7 is solid sodium thiosulfate. Carry out the following tests and record your observations in the table below. test observations (i) Using a spatula, place 2 or 3 crystals of FA 7 into a hard-glass test-tube. Heat gently for several seconds, then heat strongly. (ii) To a 1 cm depth of dilute sulfuric acid in a boiling tube, add a few crystals of FA 7. Observe until no further change occurs, then warm the mixture, gently and carefully. (iii) To a 1 cm depth of aqueous potassium iodide in a test-tube, add a few drops of FA 6, aqueous copper(II) sulfate, then add FA 1, aqueous sodium thiosulfate, to the mixture until no further change occurs. (iv) Using your observations in (ii), complete the equation below by giving the formulae of the other two products. Na2S2O3 + H2SO4 → Na2SO4 + H2O + … + … [5]

11 9701/35/M/J/15 © UCLES 2015 [Turn over (b) FA 8 and FA 9 are aqueous solutions. Each contains one cation and one anion from those listed on pages 14 and 15. Carry out the tests and record all your observations in the table. For each test, use a 1 cm depth of FA 8 or FA 9 in a test-tube. test observations FA 8 FA 9 (i) Add aqueous sodium hydroxide. (ii) Add a few drops of aqueous silver nitrate followed by aqueous ammonia. (iii) Add aqueous ammonia. (iv) Add an equal depth of dilute sulfuric acid. (v) Add an equal depth of FA 9. (vi) Using your observations, identify three of the ions present in FA 8 and FA 9. Write ‘unknown’ next to the ion that you cannot identify directly from your observations. ions in FA 8: cation … anion … ions in FA 9: cation … anion … (vii) The ‘unknown’ ion in (vi) can be identifi ed by elimination, using the lists of ions on pages 14 and 15. Choose one positive test that would confi rm the identity of this ion. Name the reagent(s) you would use and state what you would observe if the test was positive. Do not carry out this test. ‘unknown’ ion tested for … reagent(s) … observation(s) … [8] [Total: 13]

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14 9701/35/M/J/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

15 9701/35/M/J/15 © UCLES 2015 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

16 9701/35/M/J/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. BLANK PAGE

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the May/June 2015 series 9701 CHEMISTRY 9701/35 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 May/June 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 – May/June 2015 9701 35 © Cambridge International Examinations 2015 Question Indicative material Mark 1 (a) I The following data must be shown • burette readings and titre for rough titration • 2 × 2 “box” showing both accurate burette readings 1 II Headings and units correct for accurate titration table and headings match readings. • initial / start (burette) reading / volume + unit • final / end (burette) reading / volume + unit • titre or volume / FA 3 used / added (not “difference” or “total”) + unit Units: (cm3) or / cm3 or in cm3 or cm3 by every entry 1 III All accurate burette readings recorded to 0.05 cm3 Do not award this mark if: 50(.00) is used as an initial burette reading or more than one final burette reading is 50.(00) or any burette reading is greater than 50.(00). 1 IV Two accurate titres are within 0.10 cm3. Do not award if 3rd titre > 0.10 cm3 away from either previous titre unless a further titration is also carried out which is within 0.1 cm3 of any other. Do not award the mark if any ‘accurate’ burette reading (apart from an initial 0) are given to zero dp. 1 Examiner checks and corrects titre subtractions where necessary. Examiner selects the best mean titre using a hierarchy: two identical titres within 0.05 cm3, two or more titres within 0.10 cm3 etc. Examiner subtracts (corrected) candidate’s titre from Supervisor’s titre. Award V, VI and VII if δ < 0.20 cm3 Award V and VI if 0.20 < δ <0.40 cm3 Award V if 0.40 < δ <0.60 cm3 Spread penalty: if the two ‘best’ titres are ⩾ 0.50 cm3 apart, cancel one of the Q marks 1 1 1 [7] (b) Candidate must average two (or more) titres that are all within 0.20 cm3. Working must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should normally be quoted to 2 dp rounded to the nearest 0.01. Example: 26.667 must be rounded to 26.67. Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for 0.025 or 0.075 eg 26.325; allow mean to 1 dp if all accurate burette readings were given to 1 dp and the mean is exactly correct. eg 26.0 and 26.2 = 26.1 is correct but 26.0 and 26.1 = 26.1 is incorrect. Note: The candidate’s mean will sometimes be marked as correct even if it is different from the mean calculated by the Examiner for the purpose of assessing accuracy. 1 [1]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 35 © Cambridge International Examinations 2015 Question Indicative material Mark (c)(i)(ii) Correctly calculates Concentration = 0.1 × 0.900 = 0.09(00) and No. of moles = (i) × (b)/1000 1 (iii)(iv) Correctly calculates No. of moles of I2 = 0.5 × (ii) and Concentration of I2 = (iii) × 1000/25 1 (v) Equation correctly balanced 2Fe3+ + 2I– → 2Fe2+ + I2 and use of 2:1 mole ratio: answer to (v) = 2 × (iv) 1 (vi) Two steps are required: • Mr = 38.56 / (v) • Mass of water = Mr – (55.8 + 18 + [2 × 96.1]) or Mr – 266 1 Correctly calculates x from mass of water moles of water = mass / 18 and answer expressed to nearest integer 1 Final answers to (i) – (v) shown to 2 – 4 sf (minimum 4 steps attempted) 1 [6] [Total: 14] 2 (a) Initial and highest thermometer readings shown and temperature rise correctly calculated with unambiguous headings and correctly displayed units. 1 Examiner to calculate Supervisor’s and candidate’s ∆T. Calculate the difference between the two values. III and IV awarded dependant on comparability between Supervisor’s and candidate’s ∆T values. 1 1 [3] (b)(i)(ii) Correctly calculates energy produced = 25 × 4.2 × ∆T(a) and moles of FA 6 = 0.5 × 25 / 1000 (= 0.0125) and both answers to a minimum of 2 sf 1 (iii) Correct expression ∆H = (i) / 1000 × (ii) 1 [2] (c) Precision of readings shown in (a) and (c): all four thermometer readings shown to 0.0 or 0.5 ºC 1 Examiner to calculate Supervisor’s and candidate’s ∆T. Calculate the difference between the two values.

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 35 © Cambridge International Examinations 2015 Marks awarded dependant on comparability between Supervisor’s and candidate’s ∆T values. 1 [2] (d)(i)(ii) Correct expressions energy produced = 25 × 4.2 × ∆T(c) and ∆H = (d)(i) / 1000 x (b)(ii) 1 Correct (negative) sign shown in answers to (b)(iii) and (d)(ii) and both answers shown to 2 – 4 sf 1 [2] (e) Hess’ Law cycle drawn to show • displacement equation across top • left hand downward arrow, labelled (b)(iii) or calculated value • right hand downward arrow, labelled (d)(ii) or calculated value or allow from clear use of equations: Fe equation reversed and added to Zn equation or arrows showing correct directions 1 Correctly calculates (b)(iii) – (d)(ii), with correct sign. 1 [2] (f)(i) Correctly calculates: max % error = (2 x 0.5 / ∆T(c)) × 100 1 (ii) One of the following: • use a more concentrated solution of copper(II) sulfate (and larger quantities of metals) • use a lid with hole for thermometer or another specific suggestion to improve insulation • plot a cooling curve • use a larger volume / use a burette / pipette to reduce percentage error in volume • use a pipette / burette instead of a measuring cylinder 1 [2] [Total: 13]

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 35 © Cambridge International Examinations 2015 FA 7 = Na2S2O3(s); FA 8 = Zn(NO3)2(aq); FA 9 = BaCl 2(aq) 3 (a)(i) Any two observations from the following: • solid melts / dissolves or changes to liquid / solution • condensation (inside tube) or steam / water vapour / water / steamy fumes (not white fumes) • effervescence • (blue) litmus turns red • (dark) brown residue obtained or yellow solid • bad egg smell 1 (ii) White / off-white / cream / yellow ppt / solid obtained (in either part of (ii)) 1 Gas turns potassium manganate(VII) to colourless 1 (iii) Any two observations from the following: • brown / yellow-brown / green-brown (mixture / precipitate) obtained (at first) • changes to white / off-white (ppt) (when FA 1 added) • (colourless) solution formed / ppt / solid soluble (with excess FA 1) 1 (iv) Equation concludes with: … + S + SO2 1 [5] (b) test observations FA 8 FA 9 (i) + NaOH white ppt soluble in excess [1] (ii) + AgNO3 then NH3 white ppt soluble [1] (iii) + NH3 white ppt soluble in excess [1] (iv) + H2SO4 no change / no reaction / no ppt (not clear solution) white ppt [1] (v) + FA 9 no change / no reaction / no ppt (not clear solution) [1]

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 35 © Cambridge International Examinations 2015 3 (b)(vi) 3 identifications correct = two marks Any 2 identifications correct = one mark FA 8: cation is Zn2+ / zinc; anion is unknown FA 9: cation is Ba2+ / barium; anion is Cl – / chloride 1 1 (vii) unknown ion = NO3 – reagent(s) = NaOH and Al / Zn (and warm) observation(s) = (gas) turns red litmus blue or ammonia produced 1 [8] [Total: 13]