Cambridge A Level Chemistry 9701 — 2015 May/June 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 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 9701/33 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 10 printed pages and 2 blank pages. [Turn over IB15 06_9701_33/4RP © UCLES 2015 *0942652192* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/33/M/J/15 © UCLES 2015 1 HA is an organic acid. Solution FA 1 was prepared by dissolving 13.1 g of solid HA in each dm3 of solution. You are to determine the relative molecular mass, Mr, of HA by titration with aqueous sodium hydroxide. The equation for the reaction between HA and sodium hydroxide is given below. HA(aq) + NaOH(aq) → NaA(aq) + H2O(l) FA 1 is a solution containing 13.1 g dm–3 of organic acid, HA. FA 2 is 0.100 mol dm–3 sodium hydroxide, NaOH. bromothymol blue indicator (a) Method ● Fill the burette with FA 1. ● Use the pipette to transfer 25.0 cm3 of FA 2 into a conical flask. ● Add a few drops of bromothymol blue indicator. This indicator is blue in alkali and yellow in acid solutions. ● 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 certain 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 FA 1 added in each accurate titration. [7] (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 1. [1] I II III IV V VI VII

3 9701/33/M/J/15 © UCLES 2015 [Turn over (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 sodium hydroxide present in the volume of FA 2 pipetted into the conical fl ask. moles of NaOH = … mol (ii) Use your answer to (c)(i) and the equation on page 2 to determine the number of moles of organic acid, HA, used to neutralise 25.0 cm3 of FA 2. moles of HA = … mol (iii) Use your answers to (b) and (c)(ii) to calculate the number of moles of HA in 1 dm3 of FA 1. moles of HA in 1 dm3 of FA 1 = … mol (iv) Calculate the relative molecular mass, Mr, of the organic acid, HA. Mr of HA = … [4] (d) A student carrying out this method correctly with the same concentration of reactants obtained a titre of 28.30 cm3. Would this give a larger or smaller value of Mr than yours? Explain your answer. … … … [1] [Total: 13]

4 9701/33/M/J/15 © UCLES 2015 2 You are to determine the enthalpy change for the neutralisation reaction given below. HA(aq) + NaOH(aq) → NaA(aq) + H2O(l) You will be using solutions of different concentrations from those in Question 1. FA 3 is 1.80 mol dm–3 HA. FA 4 is aqueous sodium hydroxide, NaOH. (a) Method Read through the instructions carefully and prepare a table below for your results before starting any practical work. ● Support the plastic cup in the 250 cm3 beaker. ● Rinse and fill the burette with FA 3. ● Use the measuring cylinder to transfer 25 cm3 of FA 4 into the plastic cup. ● Place the thermometer in the plastic cup and record the temperature of the solution. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. ● Run 5.00 cm3 of FA 3 into the cup. Stir, and record the new temperature of the solution and the volume of FA 3 added. ● Run a second 5.00 cm3 of FA 3 into the cup. Stir and record the new temperature and the total volume of FA 3 added. ● Continue adding FA 3 in 5.00 cm3 portions. Stir and record each new temperature and total volume of FA 3 until a total of 45.00 cm3 has been added. Results [4] (b) Plot a graph of temperature (y-axis) against total volume of FA 3 added (x-axis) on the grid opposite. The temperature axis should allow you to include a point at least 2 °C greater than the maximum temperature recorded. I II III IV

5 9701/33/M/J/15 © UCLES 2015 [Turn over Draw the best fi t smooth curve or straight line through the two sets of points, one for the increase in temperature of the mixture and the other for the cooling of the solution once the reaction is complete. Extrapolate the two lines and determine the maximum increase in temperature and the corresponding volume of FA 3 added for this increase in temperature. maximum temperature increase = … °C volume of FA 3 = … cm3 [4] I II III IV

6 9701/33/M/J/15 © UCLES 2015 (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 HA present in the volume of FA 3 recorded in (b). moles of HA = … mol (ii) Using your answers to (b), calculate the heat energy produced when FA 3 neutralised 25 cm3 of sodium hydroxide. (Assume that 4.2 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 °C.) heat energy produced = … J (iii) Calculate the enthalpy change of neutralisation, in kJ mol–1, for the reaction below. HA(aq) + NaOH(aq) → NaA(aq) + H2O(l) enthalpy change = … … kJ mol–1 (sign) (value) [4] (d) The maximum error in a single thermometer reading is ±0.5 °C. Calculate the maximum percentage error in the increase in temperature recorded in (b). maximum percentage error = … % [1] (e) When carrying out thermochemistry experiments in an A Level laboratory, the plastic cup is usually placed in a glass beaker. Give a reason for the use of the glass beaker. … … [1] (f) Apart from using a thermometer calibrated to a greater level of precision, suggest one improvement that could be made to the method carried out in (a). … … [1] [Total: 15]

7 9701/33/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. 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. Before starting your practical work, half fi ll the 250 cm3 beaker with water. Heat it to approximately 80 °C, then turn off the Bunsen burner. This will be used as a hot water bath. (a) FA 5 is the salt of another organic acid. FA 6 is a salt containing two cations and one anion from those listed in the Qualitative Analysis Notes on pages 10 and 11. Carry out the following tests and record your observations in the table below. test observations (i) To a 1 cm depth of dilute sulfuric acid in a test-tube, add fi ve drops of potassium manganate(VII) then a small spatula measure of FA 5. Shake the tube then place it in the hot water bath. (ii) Place a spatula measure of FA 6 in a hard-glass test-tube. Heat gently and test any gas evolved with litmus paper. (iii) To a 4 cm depth of water in a boiling tube, add and dissolve a spatula measure of FA 6. Use portions of this solution, aqueous FA 6, for tests (iv) – (vi).

8 9701/33/M/J/15 © UCLES 2015 test observations (iv) To a 1 cm depth of aqueous FA 6 in a test-tube, add aqueous ammonia. (v) To a 1 cm depth of aqueous FA 6 in a test-tube, add a 1 cm depth of aqueous barium chloride followed by dilute hydrochloric acid or a 1 cm depth of aqueous barium nitrate followed by dilute nitric acid. (vi) To a 1 cm depth of aqueous FA 6 in a test-tube, add a small spatula measure of FA 5 and shake the mixture. Keep this mixture for the test in part (b). (vii) Identify as many of the ions in FA 6 as possible from your observations. FA 6 contains … [9] (b) A student suggests that one of the cations in FA 6 was oxidised in test (a)(vi). (i) Name a reagent you would use to fi nd out whether the student was correct. reagent … (ii) Use your reagent to carry out a test on the mixture from (a)(vi). Record your observations below. State and explain whether the student was correct. observations … … conclusion … [3] [Total: 12]

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10 9701/33/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

11 9701/33/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

12 9701/33/M/J/15 © UCLES 2015 BLANK PAGE 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.

® 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 9701/33 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 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 33 © Cambridge International Examinations 2015 Question Indicative material Mark Total 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 1 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 to 0.05 cm3 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 Two accurate titres 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 readings (apart from 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 <0.30 cm3 Award V if 0.30 < δ < 0.50 cm3 Spread penalty: if the two ‘best’ titres are ⩾ 0.50 cm3 apart, cancel one of the Q marks 1 1 1 [7]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 33 © Cambridge International Examinations 2015 (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 titres selected. The mean should normally be quoted to 2 dp rounded to the nearest 0.01. Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for 0.025 or 0.075 e.g. 26.325; allow mean to 1 dp if all accurate burette readings were given to 1 dp and the mean is exactly correct. e.g. 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] (c)(i)(ii) Correctly calculates 1000 25 0.1× = 2.5(0) × 10–3 and (ii) = (i) 1 (iii) Correctly calculates ) ( 1000 ) )( ( b ii c × 1 (iv) Correct expression ) ( 13.1 iii or correct answer if no working 1 All answers to (iii) and (iv) are given to 3 or 4 sf (minimum of 3 parts attempted) 1 [4] (d) If candidate titre < 28.30 cm3, student’s Mr larger as smaller concentration / molarity / moles in 1 dm3 of HA / FA 1 than candidate (for same mass) If candidate titre > 28.30cm3, reverse argument to above If candidate titre = 28.30cm3 no change / no difference in Mr as concentration same as HA / FA 1 (owtte) 1 [1] Qn 1 [13]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 33 © Cambridge International Examinations 2015 Question Indicative material Mark Total 2 (a) I Table for 10 sets of results with unambiguous headings and correctly displayed units or table for 9 sets of results with separate line for initial T or table for 9 sets of results with column for initial T. 1 II All volumes (apart from 0) recorded to 1 or 2 dp and all temperatures to 0.0 or 0.5 ºC. At least one thermometer reading should be recorded to 0.5 ºC. (Minimum 8 readings) 1 Examiner to calculate Supervisor’s and candidate’s maximum ∆T. Calculate the difference between the two values. III and IV awarded dependant on comparability between Supervisor’s and candidate’s ∆T value. 1 1 [4] (b) I Linear scales chosen so that graph occupies more than half the available length for both axes (including extra 2 ºC for y-axis). and axes correctly labelled 1 II All points recorded accurately plotted (within ½ small square and in the correct square, those on lines must be correctly centred). (If blobs shown then they must be correctly centred.) 1 III Two lines of best fit drawn – one for increasing temperature and one for decreasing temperature. (Allow a best fit (balanced points) straight line even if a smooth curve is more suitable for either or both.) 1 IV Correct ∆T using correct readings from graph (Tmax to within 0.2 ºC of examiner value) and correct V recorded from the intersection on graph (to within 0.5 cm3) (Tinitial may come from table or from graph plot or intercept on y-axis.) 1 [4] (c) (i) Correctly calculates 1000 ) ( 1.80 b V × to minimum 2 sf 1 (ii) Correctly calculates (25 + V(b)) x 4.2 × ∆T to min 2sf 1 (iii) Correct expression 1000 ) )( ( ) )( ( × i c ii c 1

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 33 © Cambridge International Examinations 2015 Answer given to 2 to 4 sf with negative sign 1 [4] (d) Correctly calculates ) T( 100 1.0 b ∆ × to minimum 2 sf 1 [1] (e) Safety – to prevent plastic cup tipping over / greater stability or (Reduce) heat loss – air jacket / air trapped (owtte) 1 [1] (f) Use burette / pipette for FA 4 / instead of measuring cylinder. or Use smaller volumes close to max T 1 [1] Qn 2 [15]

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 33 © Cambridge International Examinations 2015 Question Indicative material Mark Total FA 5 = (CO2)2Na2(s); FA 6 = (NH4)2Fe(SO4)2.6H2O(s) 3 (a) (i) purple / pink (solution) turns colourless / (potassium) manganate(VII) turns colourless / decolourises / purple (colour) disappears 1 (ii) (gas) turns (damp) (red) litmus blue / litmus goes blue Either condensation / liquid / water (further up tube) / water vapour / steamy fumes (not white fumes) or (green solid / contents of tube / FA 6) turn(s) white / (light) brown Allow yellow but not bright yellow. Do not allow dark brown. 1 1 (iv) green ppt insoluble in excess (Green may be qualified by intensity but not by hue – allow light / dark / dirty green but not grey–green / blue– green.) turning brown (in air) 1 1 (v) white ppt insoluble in acid Allow white ppt insoluble if “insoluble” clearly a separate line near bottom of box / next to adding acid. 1 (vi) solution turns yellow 1 (vii) ammonium / NH4 + from correct observation in (ii) (red litmus turns blue / ammonia produced / ...) iron(II) / Fe2+ and sulfate / SO4 2– 1 1 [9] (b) (i) Selects NH3 / NaOH or (acidified) KMnO4 1 (ii) green ppt or purple / KMnO4 decolourised / solution turns yellow (Allow solution turns orange / orange–brown / yellow– brown) 1 Student incorrect / cation not oxidised as still iron(II) (owtte) or Student incorrect / cation not oxidised as oxidation occurs with KMnO4 (if used) If brown ppt in (ii) with alkali allow student correct as now Fe3+ or if purple not decolourised allow student correct as already oxidised. (Allow (acidified) potassium dichromate / K2Cr2O7 as reagent and orange to green in obs and conclusion analogous to that for KMnO4.) 1 [3] Qn 3 [12]