Cambridge A Level Chemistry 9701 — 2012 Oct/Nov 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 a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fl uid. DO NOT WRITE IN ANY BARCODES. Answer all questions. 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 11 and 12. 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 Advanced Practical Skills 1 October/November 2012 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confi dential Instructions UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certifi cate of Education Advanced Subsidiary Level and Advanced Level This document consists of 12 printed pages. [Turn over IB12 11_9701_35/5RP © UCLES 2012 *1616386832* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/35/O/N/12 © UCLES 2012 For Examiner’s Use 1 You are to investigate the temperature change when a piece of magnesium ribbon is added to hydrochloric acid. You will measure the temperature at regular intervals during the reaction. FA 1 is approximately 2 mol dm–3 hydrochloric acid, HCl. You are also provided with magnesium ribbon. Read through the instructions carefully before starting any practical work. (a) Method ● Curl or fold the magnesium ribbon so that it will just fit in the bottom of the plastic cup. Remove the magnesium from the cup. ● Support the plastic cup in a 250 cm3 beaker. ● Use a measuring cylinder to transfer 50 cm3 of FA 1 into the empty plastic cup. ● Measure and record in the table below, the initial temperature of the acid in the cup. ● Start the stop watch. Measure and record the temperature of FA 1 in the cup after 1 minute, 2 minutes and 3 minutes. ● At time 3½ minutes, add the curled or folded magnesium to the FA 1 in the cup and stir the mixture. Make sure the magnesium is submerged in the acid. ● From time 4 minutes, continue to measure the temperature of the contents of the cup to complete the table. Results time / min 0 1 2 3 4 5 6 7 8 9 10 temperature / °C [1] (b) (i) On the axes opposite, plot the temperature (y-axis) against time (x-axis). The temperature axis should allow you to include a point at least 5 °C greater than the maximum temperature recorded.

3 9701/35/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use (ii) Complete the graph to show how the temperature of the contents of the cup varies with time. ● Draw one straight line through the points between time 0 minutes and 3 minutes. ● Draw one straight line through the points between time 5 minutes and 10 minutes. ● Extrapolate these two lines and draw a vertical line at time 3½ minutes. [4]

4 9701/35/O/N/12 © UCLES 2012 For Examiner’s Use (c) Calculation (i) Use your graph to determine the change in temperature at 3½ minutes. change in temperature = ………… °C (ii) In the experiment you have just carried out, explain how you know that the hydrochloric acid was in excess. … … (iii) One source of error in this experiment is due to the accuracy to which the thermometer can be read. What is the maximum error in a single temperature reading on a thermometer with graduations at 1 °C? maximum error = … °C Calculate the maximum percentage error when measuring a temperature rise of 7.5 °C. maximum percentage error = … % (iv) Apart from errors associated with the thermometer, suggest one signifi cant source of error in the procedure used in this experiment. Suggest an improvement that could be made to reduce this error. … … … (v) The experiment was repeated on another day when the temperature of the room was much higher than when the original experiment was carried out. Discuss the effect of this higher room temperature on the results of the experiment. … … … … [7] [Total: 12]

5 9701/35/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use I II III IV V VI VII 2 The concentration of the acid, FA 2, can be found by titrating it against aqueous sodium carbonate of known concentration. FA 2 is hydrochloric acid, HCl. FA 3 is sodium carbonate, Na2CO3. methyl orange indicator You are to determine the concentration of FA 2. (a) Method ● Weigh a 100 cm3 beaker. ● Weigh out between 1.3 g and 1.5 g of FA 3 into this beaker. ● Record the weighings and the mass of FA 3 added. mass of FA 3 = … g ● Add about 50 cm3 of distilled water to the beaker. ● Stir with a glass rod until all the solid has dissolved. ● Pour the solution from the beaker into the 250 cm3 graduated (volumetric) flask. ● Wash the beaker with distilled water and add the washings to the flask. ● Make up the contents of the graduated flask to the 250 cm3 mark with distilled water. ● Invert the flask as many times as you think necessary to mix the solution of FA 3 thoroughly. ● Fill the burette with FA 2. ● Pipette 25.0 cm3 of the solution of FA 3 into a conical flask. ● Add methyl orange indicator. ● Titrate the solution of FA 3 with FA 2. ● 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 2 added in each accurate titration. [7]

6 9701/35/O/N/12 © UCLES 2012 For Examiner’s Use (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 3 required … cm3 of FA 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 how many moles of sodium carbonate were present in 25.0 cm3 of the solution you pipetted for the titration. [Ar: C, 12.0; O, 16.0; Na, 23.0] moles of Na2CO3 = … mol (ii) The equation for the reaction between hydrochloric acid and sodium carbonate is shown below. Na2CO3 + 2HCl → 2NaCl + CO2 + H2O Use your answers to (b) and (c)(i) to calculate the concentration, in mol dm–3, of the hydrochloric acid, FA 2. concentration of HCl, FA 2 = … mol dm–3

7 9701/35/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use (iii) FA 2 is hydrochloric acid, HCl, made using 50.0 cm3 of FA 1 diluted to 1.00 dm3 with distilled water. Calculate the concentration, in mol dm–3, of the hydrochloric acid, FA 1. concentration of HCl, FA 1 = … mol dm–3 [5] [Total: 13]

8 9701/35/O/N/12 © UCLES 2012 For Examiner’s Use 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) You are provided with solutions FA 4, FA 5 and FA 6 and solid FA 7. Each of these contain a transition metal ion. (i) Carry out the following tests on FA 4. test observations To 1 cm depth of FA 4 in a test-tube, add an equal depth of concentrated hydrochloric acid with care. To 1 cm depth of FA 4 in a test-tube, add aqueous ammonia. To 1 cm depth of FA 4 in a test-tube, add aqueous silver nitrate. To 1 cm depth of FA 4 in a test-tube, add an equal depth of aqueous potassium iodide then, add a few drops of starch solution.

9 9701/35/O/N/12 © UCLES 2012 [Turn over For Examiner’s Use (ii) From these tests identify FA 4. … (iii) Suggest what happened to the potassium iodide in its reaction with FA 4. Use your practical results to explain your answer. … … [6] (b) FA 5, FA 6 and FA 7 each contain compounds of the same transition element. (i) Complete the following table. test observations To 1 cm depth of aqueous iron(II) sulfate in a test-tube, add a few drops of FA 5. To 1 cm depth of FA 6 in a test-tube, add an equal depth of aqueous sodium hydroxide then, add 1 cm depth of hydrogen peroxide. To 1 cm depth of FA 6 in a test-tube, add aqueous barium chloride or aqueous barium nitrate then, add an excess of either hydrochloric acid or nitric acid. To 1 cm depth of hydrogen peroxide in a boiling tube, add a small spatula measure of FA 7. (ii) From these tests identify FA 6. Explain how your observations support this conclusion. identity … evidence for cation … … evidence for anion … …

10 9701/35/O/N/12 © UCLES 2012 For Examiner’s Use (iii) It was suggested that Fe2+ was oxidised when iron(II) sulfate reacted with FA 5. To 1 cm depth of aqueous iron(II) sulfate in a test-tube add FA 5 dropwise until a pale permanent pink colour persists. Devise and carry out a test to show that the Fe2+ ions in this solution have been oxidised. Record the test used and the result obtained in the space below. [9] [Total: 15]

11 9701/35/O/N/12 © UCLES 2012 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 lead(II), Pb2+(aq) white ppt. soluble in excess white 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 [Lead(II) ions can be distinguished from aluminium ions by the insolubility of lead(II) chloride.]

12 9701/35/O/N/12 © UCLES 2012 2 Reactions of anions ion reaction carbonate, CO3 2– CO2 liberated by dilute acids chromate(VI), CrO4 2–(aq) yellow solution turns orange with H+(aq); gives yellow ppt. with Ba2+(aq); gives bright yellow ppt. with Pb2+(aq) chloride, Cl –(aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)); gives white ppt. with Pb2+(aq) bromide, Br –(aq) gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq)); gives white ppt. with Pb2+(aq) iodide, I –(aq) gives yellow ppt. with Ag+(aq) (insoluble in NH3(aq)); gives yellow ppt. with Pb2+(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) or with Pb2+(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 dichromate(VI) from orange to green 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. University of 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.

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2012 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 October/November 2012 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

Page 2 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2012 9701 35 © Cambridge International Examinations 2012 Question Sections Indicative material Mark Total 1 (a) PDO Recording Table completed and all temperatures recorded to 0.5°C. Must include at least one ending in .0 and one ending in .5. 1 [1] (b) (i) (ii) PDO Layout PDO Layout MMO Collection PDO Layout Axes labelled temperature or T / °C or (°C) or temperature in °C (y-axis) and time (x-axis) or t / minutes etc. Linear scales chosen so that graph occupies at least half the available length of both axes. This includes the 5oC extension. Plotting accurate to within half a small square. Must plot all readings taken – minimum 8. 2 straight lines drawn (0 to 3 minutes and 5 to 10 minutes). 3 appropriate lines drawn including extrapolations. 1 1 1 1 [4] (c) (i) (ii) (iii) (iv) (v) ACE Interpretation ACE Conclusions ACE Interpretation ACE Improvement ACE Conclusions ∆T calculated. Examiner to check from graph and calculate to nearest .5 °C. Candidate’s answer must be correct to nearest .5 °C. dp not needed for .0 but can include more sf if appropriate. Allow ∆T at 3 ½ minutes, even if not max, provided some indication on graph. All the magnesium disappeared / reacted / dissolved / gone. Must include idea of totality. (NOT stops fizzing) Error in one temperature reading = 0.5 (°C) Maximum % error = 0.5 × 2 / 7.5 × 100 = 13.3% (ecf 2 × error). Expression or correct answer but conditional on answer to 1 reading. Heat loss and add lid/cover/ top. (allow thermos flask) ANY 2 from Higher (initial and) final/ maximum temperature / all temperatures higher. (not temperatures higher) No effect on ∆T. Maximum temperature rise achieved quicker / reacts faster. 1 1 1 1 1 1 1 [7] [Total:12]

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2012 9701 35 © Cambridge International Examinations 2012 2 (a) MMO Collection PDO Layout PDO Recording PDO Recording I Mass of FA 3 used between 1.3 and 1.5 g. Subtraction must be correct from unambiguous weighings. II Records initial and final burette readings and titre for rough. Tabulates and records initial and final burette readings and volume of FA 2 run from burette for all accurate titrations. Not awarded if final is 50 / 50.0 / 50.00 more than once or if 50 etc is used in any initial reading. (One accurate titre is sufficient.) III Appropriate headings and units in accurate titrations. Only acceptable initial / final (burette) reading / volume or reading or volume at start / finish / beginning / end then volume used/volume added / FA 2 used / titre. Units are /cm3, (cm3) or volume in cm3. IV All burette readings, apart from the rough, recorded to 0.05 cm3 (this includes 0.00). Two (minimum) accurate titrations needed. 1 1 1 1 Examiner to check subtractions, round any burette reading to nearest 0.05 cm3 and then select the best titre using the hierarchy, two identical; two within 0.05 cm3, two within 0.1 cm3 etc., to calculate mean. This Examiner’s value should be compared with Supervisor’s mean titre taking into account the masses used by the Supervisor and the candidate. Candidate titre x Supervisor mass/ candidate mass. The candidate number, candidate’s titre, difference from the Supervisor and mark awarded should be recorded on the template. This should be attached securely to the Supervisor’s script. MMO Quality V, VI and VII Award V, VI and VII for a mean within 0.20 cm3. Award V and VI for a mean K0.20 and Y0.40 cm3. Award V for a mean K0.40 and I0.60 cm3.= Spread penalty Titres (selected by Examiner) differ by ≥ 0.5 or only one accurate titration –1. This mark is deducted from those awarded in V to VII but no negative marks. 3 [7] 2 (b) PDO Display Calculation of mean. Candidate must average two (or more) accurate titres that are within 0.20 cm3 of another. Working must be shown or ticks must be put next to the two (or more) accurate readings selected. 1

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2012 9701 35 © Cambridge International Examinations 2012 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. Do not award this mark if: any selected titre is not within 0.20 cm3 of any other selected titre; the rough titre was used to calculate the mean; the candidate carried out only 1 accurate titration; burette readings were incorrectly subtracted to obtain any of the accurate titre values. 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] 2 (c) (i) (ii) (iii) PDO Display ACE Interpretation ACE Conclusions ACE Interpretation ACE Conclusions Working shown; mass/106 is minimum required. Candidate’s mass of sodium carbonate 106 × 10 Answer correctly calculated to 3 to 4 sf. Allow ecf for transcription error in mass or incorrect Mr but not if volume included. Correct use of 2. Correct calculation of concentration (b) (i) 1000 2× × (3 to 4 sf) Ecf possible for no 2 or incorrect use of 2. Expression or correct answer to (c)(ii) × 20 (3 to 4 sf only if 20 not shown). Penalise incorrect sf only once. 1 1 1 1 1 [5] [Total: 13]

Page 5 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2012 9701 35 © Cambridge International Examinations 2012 FA 4 is CuCl2(aq); FA 5 is KMnO4(aq); FA 6 is MnSO4(aq); FA 7 is MnO2. 3 (a) (i) (ii) (iii) MMO Collection ACE Conclusions ACE Conclusions Solution / FA 4 / liquid goes from blue to green or green- yellow / yellow-green. (Pale) blue precipitate formed AND dissolves to dark / royal blue solution (not dark / deep blue ppt). White precipitate. Brown / qualified brown / precipitate / solution (not red- brown or orange) AND goes blue-black or dark blue or black (solution or solid). FA 4 is copper(II) chloride (one piece of evidence needed for Cu2+ and Ag+ test for Cl–). Iodide was oxidised (to iodine)/ KI oxidised to iodine / iodine was formed with evidence / KI oxidised needs evidence of iodine. (not iodide is a reducing agent) 1 1 1 1 1 1 [6] (b) (i) (ii) (iii) MMO Collection MMO Decisions ACE Conclusions MMO Decisions ACE Improvements Solution / FeSO4 / liquid goes from green to yellow / green to colourless / stays colourless (not no change). Solution / FA 5 / liquid goes from purple to colourless / purple to yellow. (penalise no solution or initial colour only once in (a)(i) and (b)(i)) Buff / off-white / light brown / beige precipitate. Goes brown / goes darker brown / black and bubbles / fizzing / (it/gas) relights glowing splint. White precipitate AND insoluble in dilute acid. Fizzing/bubbles/effervescence and relights a glowing splint (or gas test in point above). Conclusion: FA 6 is manganese(II) (needs II) (with obs to show some evidence) sulfate (with obs to show some evidence). Uses NaOH(aq) or NH3(aq). Red-brown / orange-brown / dark brown / rust precipitate formed (not red). 1 1 1 1 1 1 1 1 1 [9] [Total: 15]