Cambridge A Level Chemistry 9701 — 2015 May/June Paper 3 · Variant 2

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 9701/32 Paper 3 Advanced Practical Skills 2 May/June 2015 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confi dential Instructions MODIFIED LANGUAGE 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_32/FP © UCLES 2015 *0695536058* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/32/M/J/15 © UCLES 2015 1 In this question you will determine the percentage purity of a sample of contaminated sodium carbonate. FB 1 is a solution of the contaminated sodium carbonate. You will fi rst dilute FB 1 and then titrate the diluted solution using hydrochloric acid. 2HCl (aq) + Na2CO3(aq) → 2NaCl (aq) + H2O(l) + CO2(g) FB 1 was prepared by dissolving 125 g of contaminated sodium carbonate, Na2CO3, in distilled water and making the solution up to 1 dm3. FB 2 is 0.100 mol dm–3 hydrochloric acid, HCl. methyl orange indicator (a) Method Dilution ● Fill the burette with FB 1. ● Run between 13.00 and 13.50 cm3 of FB 1 into the 250 cm3 volumetric (graduated) flask. Record the volume in the space below. volume of FB 1 = … cm3 ● Fill the volumetric flask to the line with distilled water. Stopper the flask and shake it to ensure thorough mixing. ● Label this flask FB 3. Titration ● Rinse the burette thoroughly with distilled water and then with a little of solution FB 2. ● Fill the burette with FB 2. ● Use the pipette to transfer 25.0 cm3 of FB 3 into a conical flask. ● Add 5-10 drops of methyl orange indicator. ● Perform a rough titration and record your burette readings in the space below. The rough titre is … cm3. ● Do 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 FB 2 added in each accurate titration. [8] I II III IV V VI VII VIII

3 9701/32/M/J/15 © UCLES 2015 [Turn over I II III IV V (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 FB 3 required … cm3 of FB 2. [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 hydrochloric acid present in the volume of FB 2 calculated in (b). moles of HCl = … mol (ii) Calculate the number of moles of sodium carbonate present in 25.0 cm3 of FB 3. moles of Na2CO3 = … mol (iii) Calculate the concentration, in mol dm–3, of sodium carbonate in FB 3. concentration of Na2CO3 in FB 3 = … mol dm–3 (iv) Calculate the concentration, in mol dm–3, of sodium carbonate in FB 1. concentration of Na2CO3 in FB 1 = … mol dm–3 (v) Calculate the percentage purity by mass of the sodium carbonate in the contaminated sample used to prepare solution FB 1. (Ar: C, 12.0; O, 16.0; Na, 23.0) percentage purity by mass = … % [5] [Total: 14]

4 9701/32/M/J/15 © UCLES 2015 2 In this experiment you will determine the percentage by mass of magnesium in a mixture of magnesium and iron. To do this you will measure the heat given out by the reaction of the mixture with excess hydrochloric acid. You should assume that only the magnesium in the mixture will react with the acid. FB 4 is the mixture of magnesium and iron. FB 5 is 2.00 mol dm–3 hydrochloric acid, HCl. (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 a 250 cm3 beaker. ● Use the measuring cylinder to transfer 40 cm3 of FB 5 into the plastic cup. ● Weigh the stoppered container with the FB 4 and record the mass. ● Measure and record the initial temperature of the solution in the plastic cup. ● Add all the sample of FB 4 to the acid in the plastic cup carefully to minimise acid spray. ● Stir the mixture and record the maximum temperature that is reached. ● Weigh the stoppered container and any residual metal mixture. Record the mass. ● Record the mass of metal added to the acid. [4] (b) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Use your value for the maximum temperature rise to calculate the heat energy produced in the reaction. (Assume that 4.2 J are required to increase the temperature of 1.0 cm3 of solution by 1.0 °C.) heat energy produced = … J I II III IV

5 9701/32/M/J/15 © UCLES 2015 [Turn over (ii) The molar enthalpy change, ∆H, for the reaction shown below is – 457 kJ mol–1. Mg(s) + 2HCl (aq) → MgCl 2(aq) + H2(g) Use this value and your answer to (i) to calculate the number of moles of magnesium in your reaction. moles of Mg = … mol (iii) Use your answer to (ii), to calculate the percentage by mass of magnesium in FB 4. (Ar: Mg, 24.3) percentage by mass of Mg in FB 4 = … % (iv) You have assumed that only the magnesium reacts with the acid. What other assumption have you made in using this method to determine the percentage by mass of magnesium in the mixture? … … [4] (c) (i) Calculate the maximum percentage error in the temperature rise. maximum percentage error = … % (ii) Using the same FB 4, the same FB 5 and no additional apparatus, describe how you could modify the experiment to reduce this maximum percentage error in the temperature rise. Explain your answer. … … … [3] [Total: 11]

6 9701/32/M/J/15 © UCLES 2015 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. (a) FB 6 is a solution containing two cations and one anion. Both of the cations are listed in the Qualitative Analysis Notes on page 10. (i) Select reagents to identify the cations in FB 6. Do tests using these reagents and record your results in the space below. The cations in FB 6 are … and … .

7 9701/32/M/J/15 © UCLES 2015 [Turn over (ii) The anion in FB 6 is the nitrate ion, NO3 –. Explain why it is diffi cult to confi rm the presence of the nitrate ion in FB 6 using the method outlined in the Qualitative Analysis Notes on page 11. … … … [6] Before starting part (b), half fi ll a 250 cm3 beaker with water and heat with a Bunsen burner to approximately 60 °C. You will use this as a hot water bath. Turn off the Bunsen burner. (b) FB 7 is a halogenoalkane. Do the following test to determine the halogen present in FB 7. test observations (i) To a 1 cm depth of ethanol in a test-tube, add a 1 cm depth of silver nitrate followed by 10 drops of FB 7, then place the test-tube in the hot water bath. The halogen present in FB 7 is … . (ii) What type of reaction has the halogenoalkane undergone? … [4]

8 9701/32/M/J/15 © UCLES 2015 (c) FB 8 and FB 9 each contain a single cation and a single anion. Do the following tests and record your observations. test observations (i) To a 1 cm depth of FB 8 in a test-tube, add FB 9 until there is no further reaction, then add aqueous barium chloride or aqueous barium nitrate. (ii) Suggest possible identities for the ions present. You will only be able to identify one of the cations. cation … anions … [5] [Total: 15]

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10 9701/32/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 9701/32/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 9701/32/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 9701/32 Paper 32 (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 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 32 © Cambridge International Examinations 2015 Question Indicative material Mark Total 1 (a) I Follows instructions – adds between 13.00 and 13.50 cm3 1 II Initial and final burette readings and titre unambiguously recorded in rough and accurate titrations. 1 III Headings and units correct for accurate titration and headings match readings. Headings: initial / final (burette) reading / volume or Reading / volume at start / finish and Volume / FB 1 added / used or titre [not “difference”] and Units: (cm3) or / cm3 or in cm3 or cm3 by every entry 1 IV All accurate burette readings (initial and final) recorded to nearest 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 V Has two uncorrected, accurate titres within 0.1 cm3 Do not award this mark if, having performed two titres within 0.1 cm3, a further titration is performed that is more than 0.1 cm3 from the closer of the two initial titres unless further titrations within 0.1 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 all burette readings to the nearest 0.05 cm3 and checks subtractions. The ‘best’ titres should be selected using the hierarchy: two (or more) identical, then two (or more) within 0.05 cm3 , then two (or more) within 0.1 cm3, etc. Examiner to calculate, correct to 2 dp, diluted vol cand titre candidate and diluted volume supervisor titre supervisor and find the difference, δ. Award VI, VII and VIII if δ ⩽ 0.02 Award VI and VII if 0.20 ⩽ δ ⩽0.04 Award VI if 0.40 ⩽ δ ⩽0.06 Spread penalty: if the two ‘best’ titres used by the examiner are more than=0.50 cm3 apart cancel one of the Q marks. 1 1 1 [8]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 32 © Cambridge International Examinations 2015 1 (b) Calculation of mean 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, 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. 1 [1] Question Indicative material Mark Total 1 (c) (i)(ii) I Uses the expression 1000 0.100 (b) × in step (i) and use of × ½ in (ii) 1 (iii) II Correctly calculates (ii) / 0.025 1 (iv) III Correctly calculates (iii) × (250 / volume diluted) 1 (v) IV Correctly calculates (iv) × (106 / 125) × 100 1 V Answers to (i) to (iv) given to 3 or 4 sf 1 [5] Qn 1 Total [14]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 32 © Cambridge International Examinations 2015 Question Indicative material Mark Total 2 (a) Table to include initial and final mass, initial and final temperature, mass added and temperature rise. All with correct units. 1 All masses recorded to the same precision and all temperatures recorded to .0 or .5 °C. 1 III Award if the difference between candidate and Supervisor is within 4.0 °C IV Award if the difference between candidate and Supervisor is within 2.0 °C 1 1 [4] 2 (b) (i) Correct answer to 4.2 × 40 × ∆T Allow answers to 2 – 4 sf 1 (ii) Correct answer to (i) / 457 000 Allow answers to 2 – 4 sf 1 (iii) Correct answer to (ii) × (24.3 / mass of mixture) × 100 Allow answers to 2 – 4 sf 1 (iv) Heat loss (not significant) or non-standard conditions (not significant) 1 [4] 2 (c) (i) Correct working or answer correct to number of sf shown: (1.0 / temp rise) × 100 1 (ii) Reduce the volume of acid to give a greater temperature rise. 1 Make sure that the acid remains in excess. 1 [3] Qn 2 Total [11]

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 32 © Cambridge International Examinations 2015 Question Indicative material Mark Total FB 6 is NH4Cl(aq) and Zn(NO3)2(aq); FB 7 is 1-iodobutane; FB 8 is Na2CO3(aq); FB 9 is H2SO4(aq) 3 (a) (i) Clear presentation of results – minimum two tests 1 Selects NaOH(aq) and NH3(aq) 1 White ppt soluble in excess with both reagents 1 Gas / NH3 turns red litmus blue when warmed with NaOH. 1 Zn2+ and NH4 + 1 (ii) Warming with NaOH in the presence of NH4 + will produce ammonia and so cannot tell if any ammonia is being produced by reduction of the nitrate ions 1 [6] 3 (b) (i) No reaction on mixing 1 Yellow ppt or if observed on mixing then amount of ppt increases. 1 Iodine 1 (ii) Substitution / hydrolysis 1 [4] 3 (c) (i) Fizzing 1 Limewater turns milky 1 White ppt with Ba2+ 1 (ii) cations: H+ 1 anions: CO3 2– and then SO4 2– and / or SO3 2– 1 [5] Qn 3 Total [15]