Cambridge A Level Chemistry 9701 — 2014 Oct/Nov Paper 3 · Variant 4

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 10 and 11. 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 9701/34 Paper 3 Advanced Practical Skills 2 October/November 2014 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 11 printed pages and 1 blank page. [Turn over IB14 11_9701_34/3RP © UCLES 2014 *7278217255* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/34/O/N/14 © UCLES 2014 1 Hydrogen peroxide, H2O2, is used in hair bleach and for skin therapies. In this experiment you will determine the concentration of a solution of hydrogen peroxide by titration with acidifi ed potassium manganate(VII). FB 1 is 0.0250 mol dm–3 potassium manganate(VII), KMnO4. FB 2 is dilute sulfuric acid, H2SO4. FB 3 is aqueous hydrogen peroxide, H2O2. (a) Method Dilution of FB 3 ● Pipette 25.0 cm3 of FB 3 into the volumetric (graduated) flask. ● Make the solution up to the mark using distilled water. ● Shake the flask thoroughly. ● This diluted solution of hydrogen peroxide is FB 4. Titration ● Fill the burette with FB 1. ● Pipette 10.0 cm3 of FB 4 into a conical flask. ● Use a measuring cylinder to add 25 cm3 of FB 2 into the same flask. ● Add FB 1 until a permanent pale pink colour is seen. ● 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 form below all of your burette readings and the volume of FB 1 added in each accurate titration. Keep solution FB 2 for use in Question 3 and solution FB 3 for use in Questions 2 and 3. [7] I II III IV V VI VII

3 9701/34/O/N/14 © UCLES 2014 [Turn over (b) From your accurate titration results, obtain a suitable value for the volume of FB 1 to be used in your calculations. Show clearly how you have obtained this value. 10.0 cm3 of FB 4 required … cm3 of FB 1. [1] (c) 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 potassium manganate(VII) present in the volume calculated in (b). moles of KMnO4 = … mol (ii) Complete the equation below for the reaction of potassium manganate(VII) with hydrogen peroxide. State symbols are not required. …KMnO4 + 5H2O2 + 3H2SO4 → K2SO4 + 2MnSO4 + …H2O + 5O2 (iii) Use your answers to (i) and (ii) to calculate the number of moles of hydrogen peroxide used in each titration. moles of H2O2 = … mol (iv) Calculate the concentration of H2O2 in FB 4, in mol dm–3. concentration of H2O2 in FB 4 = … mol dm–3 (v) Calculate the concentration of H2O2 in FB 3, in mol dm–3. concentration of H2O2 in FB 3 = … mol dm–3 [5] [Total: 13]

4 9701/34/O/N/14 © UCLES 2014 2 In this experiment you will determine the enthalpy change, ∆H, for the catalytic decomposition of hydrogen peroxide into water and oxygen. H2O2(aq) → H2O(l) + 2 1 O2(g) FB 3 is aqueous hydrogen peroxide, H2O2. FB 5 is manganese(IV) oxide, MnO2, the catalyst for the decomposition. (a) Method Read through the method before starting any practical work and prepare a table for your results in the space below. ● For the first experiment, support the plastic cup inside the 250 cm3 beaker. ● Use a measuring cylinder to transfer 40 cm3 of distilled water into the plastic cup. ● Use a measuring cylinder to add 10 cm3 of FB 3 into the plastic cup. ● Measure and record the initial temperature of the mixture. ● Add a heaped spatula measure of FB 5 to the mixture in the plastic cup. ● Stir constantly until the maximum temperature is reached and record this temperature. ● Calculate and record the temperature rise. ● Wash and wipe out your plastic cup and rinse the thermometer, ready for the second experiment. ● For the second experiment, support the plastic cup inside the 250 cm3 beaker. ● Use a measuring cylinder to transfer 30 cm3 of distilled water into the plastic cup. ● Use a measuring cylinder to add 20 cm3 of FB 3 into the plastic cup. ● Measure and record the initial temperature of the mixture. ● Add a heaped spatula measure of FB 5 to the mixture in the plastic cup. ● Stir constantly until the maximum temperature is reached and record this temperature. ● Calculate and record the temperature rise. ● Wash and wipe out your plastic cup and rinse the thermometer, ready for the third experiment. ● Carry out the third experiment in a similar way. ● Transfer 20 cm3 of distilled water into the plastic cup. ● Add 30 cm3 of FB 3 into the plastic cup. ● Measure and record the initial temperature of the mixture. ● Add a heaped spatula measure of FB 5 to the mixture in the plastic cup. ● Record the maximum temperature, then calculate and record the temperature rise. ● For the fourth experiment, use 10 cm3 of distilled water and 40 cm3 of FB 3. [5] I II III IV V

5 9701/34/O/N/14 © UCLES 2014 [Turn over (b) Using the grid below, plot a graph of the temperature rise (y-axis) against the volume of FB 3 (x-axis). Draw the line of best fi t. [4] I II III IV

6 9701/34/O/N/14 © UCLES 2014 (c) Calculation (i) Use your graph to calculate the average temperature rise for each 1.0 cm3 of FB 3 used. Show your working clearly on the graph. average temperature rise = … °C (ii) Calculate the energy released for each 1.0 cm3 of FB 3 used. (Assume that 4.2 J are needed to raise the temperature of 1.0 cm3 of solution by 1.0 °C.) energy released = … J (iii) Use your answer to 1(c)(v) to calculate the number of moles of hydrogen peroxide in 1.0 cm3 of FB 3. (If you were unable to calculate the concentration of H2O2 in FB 3, assume that it was 1.72 mol dm–3. Note: this is not the correct value.) number of moles of H2O2 = … mol (iv) Calculate the enthalpy change, in kJ mol–1, for the reaction below. H2O2(aq) → H2O(l) + 2 1 O2(g) enthalpy change = … … kJ mol–1 (sign) (value) [4] (d) Which one of the four experiments that you carried out is likely to be the least accurate? Explain your choice. … … … [1] [Total: 14]

7 9701/34/O/N/14 © UCLES 2014 [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. (a) You will carry out further experiments with aqueous hydrogen peroxide, FB 3. FB 2 is dilute sulfuric acid, H2SO4. FB 3 is aqueous hydrogen peroxide, H2O2. FB 6 is a solution containing two cations and one anion. FB 7 is a solution containing one cation and one anion. (i) To a 1 cm depth of FB 6 in a boiling tube, add aqueous sodium hydroxide until it is in excess. Then heat the tube, gently and with care. Keep the mixture for test (ii). Record your observations. Identify the cations in FB 6. observations … … … FB 6: cations are … and … (ii) To the mixture obtained from (i) add a 1 cm depth of FB 3. Shake the tube. Record your observations. observations … … … What type of reaction has taken place? Explain your answer. … …

8 9701/34/O/N/14 © UCLES 2014 (iii) To a 1 cm depth of FB 3 in a test-tube, add an equal volume of sulfuric acid, FB 2. Then add a 1 cm depth of FB 7, followed by a few drops of starch solution. Record all your observations. Draw what conclusions you can about the ions in FB 7. If no conclusion is possible, write ‘not known’. observations … … … FB 7: cation … anion … [7] (b) FB 7, FB 8 and FB 9 are aqueous solutions, each containing one cation and one anion. Note that FB 7 was also used in (a)(iii). (i) Carry out the following tests in test-tubes. Use 1 cm depths of solutions. Complete the table by recording your observations. test observations FB 7 FB 8 FB 9 add a 2 cm strip of magnesium ribbon FB 7 FB 8

9 9701/34/O/N/14 © UCLES 2014 [Turn over (ii) Suggest the identify of the cation in FB 9. Explain your answer. cation … explanation … (iii) Give the ionic equation for the reaction between FB 7 and FB 9. … (iv) From your observations, identify FB 8. … [6] [Total: 13]

10 9701/34/O/N/14 © UCLES 2014 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

11 9701/34/O/N/14 © UCLES 2014 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

12 9701/34/O/N/14 © UCLES 2014 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. 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 October/November 2014 series 9701 CHEMISTRY 9701/34 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 2014 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 2014 9701 34 © Cambridge International Examinations 2014 Question Indicative material Mark Total 1 (a) I The following data is shown • two burette readings for the rough titration • titre for rough titration • initial and final burette readings for two (or more) accurate titrations (i.e. 2 × 2 “box”) 1 II Appropriate headings and units for accurate titration and volume FB 1 added recorded for each accurate titre. Headings should match readings. • initial / start and (burette) reading / volume • final / end and (burette) reading / volume • titre or volume / FB 1 and used / added unit / cm3 or (cm3) or in cm3 or cm3 for each entry 1 III All accurate burette readings are to the nearest 0.05 cm3. The requirement to record to 0.05 applies to burette readings, including 0.00 cm3 (if this was the initial reading), but it does not apply to the titre. Do not award this mark if: • 50(.00) is used as an initial burette reading • more than one final burette reading is 50.(00) • any burette reading is greater than 50.(00) 1 IV There are two uncorrected accurate titres within 0.10 cm3 • Do not include a reading if it is labelled “rough”. • Do not award this mark if, having performed two titres within 0.10 cm3, a further titration is performed which is more than 0.10 cm3 from the closer of the initial two titres, unless a further titration, within 0.10 cm3 of any other, has also been carried out. • Do not award the mark if any ‘accurate’ burette readings (apart from initial 0) are given to zero dp. 1 Examiner rounds any burette readings to the nearest 0.05 cm3 and then selects the ‘best’ titres using the hierarchy: • two (or more) accurate identical titres (ignoring rough), then • two (or more) accurate titres within 0.05 cm3, then • two (or more) accurate titres within 0.10 cm3 etc. These best titres are used to calculate the mean corrected titre to the nearest 0.01 cm3. Award V, VI and VII if δ ≤ 0.20 (cm3) Award V and VI if 0.20 < δ ≤ 0.40 Award V, only, if 0.40 < δ ≤ 0.80 Spread penalty: if the two “best” (corrected) titres used by the Examiner were ≥ 0.50 cm3 apart, cancel one Q mark. 1 1 1 [7]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2014 9701 34 © Cambridge International Examinations 2014 Question Indicative material Mark Total (b) • Candidate averages two (or more) titres where the total spread is ≤0.20 cm3. • Working must be shown or ticks must be put next to the two (or more) accurate readings selected. • The mean should be quoted to 2 dp, and be correctly rounded to nearest 0.01 cm3. Two special cases, where the mean need not be to 2 dp: • Allow mean to 3 dp only for 0.025 or 0.075 (e.g. 26.325 cm3) • Allow mean to 1 dp, if all accurate burette readings were given to 1 dp and the mean is exactly correct. Note: the candidate’s mean will sometimes be marked correct even if it was different from the mean calculated by the Examiner for the purpose of assessing accuracy. 1 [1] (c) (i) Number of moles of KMnO4 used = 0.0250 × 1000 (b) 1 (ii) 2KMnO4 + 5H2O2 + 3H2SO4 → K2SO4 + 2MnSO4 + 8H2O + 5O2 1 (iii) + (iv) (iii) number of moles of H2O2 (in 10 cm3) = 2.5 × (i) (iv) number of moles of H2O2 (in 1.0 dm3) = 100 × (iii) Allow ecf in (iii) to incorrect equation 1 (v) Concentration in FB 3 = (iv) × 10 1 (c) Answers to parts (i), (iii), (iv) and (v) given to 3 or 4 sf A minimum of 3 answers is needed to qualify for the mark. All answers given must have appropriate sig figs. 1 [5] Qn 1 Total [13]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2014 9701 34 © Cambridge International Examinations 2014 Question Indicative material Mark Total 2 (a) I Table of data, showing all of the following: • unambiguous headings (ignore units) • four initial temperature • four final temperatures • four temperature rises correctly calculated All data must be tabulated in the space provided on page 4. 1 II Recording of data • correct units ‘covering’ all temperature readings. • all readings recorded to .0 or .5 °C, with at least one shown as .5 °C or .0 °C Minimum of six temperatures required to qualify 1 • Examiner checks Supervisor’s subtraction for temperature rise for experiment 4. • Examiner corrects thermometer readings to nearest .5 °C then subtracts. • Examiner calculates the difference between the [corrected] candidate’s and Supervisor’s temperature rise for experiment 4. Award III if ∆T increases with increase in volume of FA 3. Experiment 4 Award IV if δ ≤ 2.0 °C Award V if δ ≤ 1.0 °C If expt 4 was not carried out, examiners may award mark IV if experiment 3 is within 1.0 °C of Supervisor. 1 1 1 [5] (b) I Suitable axes and scales to graph • both axes clearly labelled (units not required) • temperature (rise) as y-axis • suitable linear scales (Points are plotted using more than half of the grid in both directions from (0,0). Must have at least one point plotted. ) 1 II Four points plotted clearly and correctly (All points plotted to within half a square and in the correct square for y-axis and on line for x-axis.) 1 III 0,0 point either plotted or used for line (within one small square) 1 IV Best fit line • Minimum 4 points on the grid are needed. This may include (0,0) if plotted. • Points above and below best fit line are “balanced”. 1 [4] (c) (i) Correctly calculates temp rise per cm3 (gradient of straight line) • All points from the best fit line must be correctly read to the nearest half square. • Points used must differ by a minimum of two large squares, along each axis. 1

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2014 9701 34 © Cambridge International Examinations 2014 (ii) Heat produced = 50 × 4.2 × temp rise calculated in (i) 1 (iii) Number of moles of H2O2 = 0.0010 × 1(c)(v) (2, 3 or 4 sig fig) 1 (iv) Correct expression including negative sign and evidence of ÷ 1000 ∆H = – (iii) (ii) × 1000 or correct answer 1 [4] (d) The first experiment, because it has the smallest temperature rise so greatest % error or smallest volume of FA 3 / H2O2 so greatest % error. or The final experiment because it has the greatest heat loss. or Identifies experiment giving most anomalous point on graph. 1 [1] Qn 2 Total [14]

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2014 9701 34 © Cambridge International Examinations 2014 Question Indicative material Mark Total FB 6 is (NH4)2Fe(SO4)2; FB 7 is KI; FB 8 is HCl; FB 9 is AgNO3 3 (a) (i) Green precipitate, insoluble in excess (NaOH) 1 (When mixture heated) gas / ammonia turns (red) litmus blue 1 Either cation in FB 6 identified from correct observations • iron(II) / Fe2+ • Ammonium / NH4 + 1 (ii) Both observations are correct • Precipitate / solid goes brown / red-brown / rust • Bubbles / fizzing / effervescence (not “gas formed”) 1 Type of reaction and justification redox (or oxidation and reduction) with any of the following: • iron(II) ions converted to iron(III) ions • hydrogen peroxide converted to oxygen • colour change indicates different oxidation states or oxidation of Fe2+ to Fe3+ or reduction of H2O2 as Fe2+ oxidised / Fe2+ changes colour or (catalytic) decomposition of H2O2 to give (H2O and) O2 or exothermic as heat is given out / temp increases 1 (iii) Yellow / orange / red-orange / brown / red-brown (not red) with FB 7 and black / blue-black / dark blue with starch 1 Both conclusions about FB 7 are correct • cation – not known • anion – iodide / I– 1 [7] (b) (i) Two observations for the Mg tests are correct. • Fizzing / bubbles / effervescence with FB 8 • Black / dark grey (solid/precipitate) with FB 9 1 (b) (i) Positive gas test performed and recorded: Gas / H2 (evolved from Mg + FB 8) pops with a lighted splint / when ignited / when burned Mark may also be credited for positive O2 test in 3(a)(ii): gas / O2 relights glowing splint / glowing splint glows brighter. 1 Remaining three observations in the table are correct • FB 7 + FB 8 – no reaction / no change • FB 7 + FB 9 – (pale) yellow precipitate • FB 8 + FB 9 – white precipitate 1 (ii) Cation in FB 9 is silver / Ag+ 1

Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2014 9701 34 © Cambridge International Examinations 2014 Question Indicative material Mark Total (iii) Ag+ + I– → AgI (ecf from FB 7+FB 9: cream ppt Br –, white ppt Cl –) (State symbols are not required but if given must be correct.) 1 (iv) FB 8 is hydrochloric acid / HCl (Allow HBr from cream / off-white ppt in table with FB 8 + FB 9) 1 [6] Qn 3 Total [13]