Cambridge A Level Chemistry 9701 — 2015 May/June 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 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 11 printed pages and 1 blank page. [Turn over IB15 06_9701_34/5RP © UCLES 2015 *4147278659* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/34/M/J/15 © UCLES 2015 1 The concentration of aqueous ammonia used in qualitative analysis is 2 mol dm–3 but it is supplied in a much more concentrated form. This is referred to as ‘.880 ammonia’. You are to determine the concentration of ‘.880 ammonia’ by titration of a solution of ammonia, FB 1, with hydrochloric acid of known concentration. The equation for the reaction is given below. NH3(aq) + HCl (aq) → NH4Cl (aq) FB 1 is a dilute solution of ammonia, NH3(aq). It was prepared by measuring out 5.91 cm3 of the ‘.880 ammonia’ and then adding distilled water until the solution had a volume of 1 dm3. FB 2 is 0.100 mol dm–3 hydrochloric acid, HCl (aq). methyl orange indicator (a) Method ● Fill the burette with FB 2. ● Use the pipette to transfer 25.0 cm3 of FB 1 into a conical flask. ● Add a few drops of methyl orange indicator. ● 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 achieve 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. [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 FB 1 required ………….. cm3 of FB 2. [1] I II III IV V VI VII

3 9701/34/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 hydrochloric acid present in the volume of FB 2 calculated in (b). moles of HCl = … mol (ii) Use your answer to (i) to determine the number of moles of ammonia present in 25.0 cm3 of FB 1, pipetted into the conical fl ask. moles of NH3 = … mol (iii) Use your answer to (ii) to calculate the concentration, in mol dm–3, of the diluted ammonia, FB 1. concentration of NH3 (diluted) in FB 1 = … mol dm–3 (iv) Use your answer to (iii) and the information on page 2 to calculate the concentration, in mol dm–3, of ‘.880 ammonia’. concentration of ‘.880 ammonia’ = … mol dm–3 [3] (d) A student analysed a different sample of concentrated ammonia and determined the concentration to be 15.0 mol dm–3. Calculate the percentage difference in concentration of the ‘.880 ammonia’ you have determined compared with that of the student. (If you have been unable to complete the calculation, assume the concentration of ‘.880 ammonia’ was 9.35 mol dm–3. This is not the correct value.) percentage difference in concentration = … % [1] [Total: 12]

4 9701/34/M/J/15 © UCLES 2015 2 You are to determine the enthalpy change of solution, in kJ mol–1, of ammonium chloride. FB 3 is approximately 9 g of solid ammonium chloride, NH4Cl. distilled water (a) Method Read through the instructions carefully and prepare a table below for your results before starting any practical work. ● Weigh the plastic cup and record the balance reading. ● Add between 2.9 and 3.1 g of ammonium chloride, FB 3, and record the new balance reading. ● Place the plastic cup in the 250 cm3 beaker. ● Pour 25 cm3 of distilled water into the measuring cylinder. ● Place the thermometer in the water and record the initial temperature in the table of results. ● Pour the 25 cm3 of distilled water into the plastic cup. ● Stir the contents of the cup and record the lowest temperature of the solution. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. ● Repeat the procedure using the other plastic cup. Use between 4.9 and 5.1 g of FB 3 for this experiment. ● Record the mass of FB 3 used and the change in temperature for each experiment. Results [5] I II III IV V

5 9701/34/M/J/15 © UCLES 2015 [Turn over (b) (i) Calculate the mean mass of FB 3 used. Give your answer to two decimal places. mean mass of FB 3 = … g (ii) Calculate the mean temperature change. Give your answer to one decimal place. mean temperature change = … °C [2] (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 NH4Cl present in the mass of FB 3 calculated in (b)(i). [Ar: H, 1.0; N, 14.0; Cl, 35.5] moles of NH4Cl = … mol (ii) Use your answers to (b)(ii) and (c)(i) to calculate the enthalpy change of solution, in kJ mol–1, of NH4Cl. (Assume that 4.2 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 °C.) enthalpy change = … … kJ mol–1 (sign) (value) [4]

6 9701/34/M/J/15 © UCLES 2015 (d) (i) Which of the two experiments in (a), the fi rst or the second, had the greater percentage error in the value calculated for the temperature change? … (ii) Given that the error in a single thermometer reading is ±0.5 °C, calculate the percentage error in the temperature change for the experiment you gave in (d)(i). percentage error = … % [1] (e) (i) A student suggested that it would have been better to calculate the enthalpy change for each experiment separately. What would be the advantage of this suggestion? Explain your answer fully. … … … (ii) Another student suggested that the procedure would be improved by covering the plastic cup with a lid. Explain whether this would improve the procedure. … … [2] [Total: 14]

7 9701/34/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. (a) FB 4 and FB 5 are solutions of salts each containing one cation 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 FB 4 FB 5 (i) To a 1 cm depth of solution in a test-tube, add aqueous ammonia. (ii) To a 1 cm depth of solution in a test-tube, add a few drops of aqueous silver nitrate. (iii) To a 1 cm depth of solution in a test-tube add a few drops of aqueous barium chloride or barium nitrate.

8 9701/34/M/J/15 © UCLES 2015 (iv) Identify both ions in FB 4. cation … anion … (v) Suggest the ions which may be present in FB 5. cations … anions … (vi) Select a reagent which could be used in a further test on FB 5 to identify the cation present. Carry out your test and record your observations. test observations To a 1 cm depth of FB 5 in a test-tube, add … The cation in FB 5 is … [7] (b) FB 6 is a pale purple salt containing two cations. (i) What does this suggest about the identity of one of the cations in FB 6? …

9 9701/34/M/J/15 © UCLES 2015 [Turn over Carry out the following tests and complete the table below. test observations (ii) Place a spatula measure of FB 6 in a hard-glass test-tube. Heat gently. (iii) Dissolve a small spatula measure of FB 6 in a 2 cm depth of distilled water in a test-tube. Use this solution for tests (iv) and (v). (iv) Pour about half the solution prepared in (iii) into a boiling tube and add aqueous sodium hydroxide, then gently warm the mixture. (v) To the remainder of the solution prepared in (iii), add a few drops of aqueous potassium iodide, then add a few drops of starch solution. (vi) Identify the cations present in FB 6. FB 6 contains … and … (vii) What type of reaction occurred when potassium iodide was added to FB 6 in (v)? … [7] [Total: 14]

10 9701/34/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 9701/34/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 9701/34/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 9701/34 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 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 34 © Cambridge International Examinations 2015 Question Indicative material Mark Total 1 (a) (i) Initial and final burette readings and titre unambiguously recorded in rough and accurate titrations. (2×2 accurate boxes) 1 (ii) Headings and units correct for accurate titration and headings match readings. Initial / final (burette) reading / volume or Reading / volume at start / finish and Titre or Volume / FB 2 added / used [not “difference”] and 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 any other 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 < 0.40 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 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) (answer to (b) × 0.1) / 1000 and (ii) = (i) and answer to 3 or 4 sf 1

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 34 © Cambridge International Examinations 2015 Question Indicative material Mark Total (iii) (c)(ii) × 1000 / 25 and answer expressed to 3 or 4 sf. 1 (iv) Correct expression is shown (c)(iii) × 1000 / 5.91 1 [3] (d) 15 – (c)(iv) × 100 / 15 or 15 – (c)(iv) × 100 / (c)(iv) 1 [1] Total [12] 2 (a) I (Table of) results with unambiguous headings (not weight) showing • 4 balance readings • 4 thermometer readings • 2 × mass FB 3 added • 2 × ∆T 1 II All balance readings recorded to the same number of dp (at least one dp) and thermometer readings to .0 or .5 ºC (minimum 2 of each) 1 III Masses of FB 3 used between the limits given in the question (2.9(0) to 3.1(0) g and 4.9(0) to 5.1(0) g) 1 Examiner corrects thermometer readings to the nearest 0.5 ºC, checks subtractions then calculates ∆T1 × m2 / ∆T2 × m1 where ∆T1 is the smaller temperature fall. Award IV if ratio falls between 0.85 and 1.15 Award IV and V if ratio falls between 0.95 and 1.05 1 1 [5] (b) (i) mean mass correctly calculated from weighings to 2 dp 1 (ii) mean temperature fall correctly calculated from thermometer readings to 1 dp Do not award if values used for calculating mean are from incorrect subtractions. 1 [2] (c) (i) Correctly calculates (b)(i) / 53.5 1

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 34 © Cambridge International Examinations 2015 Question Indicative material Mark Total (ii) Correct overall expression 25 × 4.2 × (b)(ii) (c)(i) × 1000 • fully correct = 2 marks • one error = 1 mark • two errors = 0 marks (÷ 1000 may be awarded from use to reach final answer) 1 1 Sign is + and final answers to (i) and (ii) are to 2 – 4 sf 1 [4] (d) (ii) Expression (1.0 / smaller ∆T) × 100 or correct answer 1 [1] (e) (i) Advantages: any one of two values to check concordance / check whether further experiments should be carried out / find out whether mass added is proportional to ∆T / compare the two answers 1 (ii) No improvement as T drops so no heat loss (by convection) / as reaction is endothermic OR Improvement as prevents heat gain from surroundings 1 [2] Total [14] FB 4 = MnCl 2(aq); FB 5 = MgSO4(aq) ; FB 6 = NH4Fe(SO4)2 (s) 3 (a) Correct observations for FB 4 and FB 5 in (i) Correct observations for FB 4 and FB 5 in (ii) and correct observations for FB 4 and FB 5 in (iii). 2 1

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 34 © Cambridge International Examinations 2015 test FB 4 FB 5 (i) NH3 off-white / pale brown / beige / buff ppt and insoluble in excess / ppt turns (dark) brown/darkens white ppt insol in excess (ii) AgNO3 white ppt (if excess used then insoluble) no change / no ppt / no reaction (iii) BaCl 2/ Ba(NO3)2 no change / no ppt / no reaction white ppt (if excess used then insoluble) Question Indicative material Mark Total 3 (a) (iv) FB 4: manganese(II) / Mn2+ and chloride / Cl – (If cream ppt with Ag+ allow bromide / Br –) 1 (v) FB 5: Mg2+, Al 3+, and SO 4 2–, SO 3 2– (or names) 1 (vi) selects NaOH and uses it in excess FB 5: magnesium / Mg2+ from white ppt insoluble in excess 1 1 [7] (b) (i) Transition metal (as coloured) 1 (ii) Any two of: • (pale purple) solid / crystals melt / dissolve / turn to liquid / form liquid or solution • any brown or qualified brown (liquid or solid not gas) • condensation / liquid / water (further up tube) / water vapour / steamy fumes (not white fumes) • (gas) turns (red) litmus blue (then back to red) 1 (iii) yellow / (light) brown (solution) (formed) 1 (iv) brown / rust / red-brown ppt and gas / NH3 turns (damp) (red) litmus blue 1 (v) (solution darkens) dark blue / blue-black / black colour 1 (vi) Fe3+ and NH4 + 1 (vii) redox / oxidation and reduction / oxidation of I– / reduction of Fe3+ 1 [Total: 14]