Cambridge A Level Chemistry 9701 — 2011 Oct/Nov Paper 3 · Variant 4

This document consists of 11 printed pages and 1 blank page. DC (KN/DJ) 34822/4 © UCLES 2011 [Turn over * 8 5 1 6 3 4 8 3 5 6 * UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level 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 fluid. 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 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 Advanced Practical Skills 2 October/November 2011 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions Session Laboratory For Examiner’s Use 1 2 Total

2 9701/34/O/N/11 © UCLES 2011 For Examiner’s Use 1 You are to determine the enthalpy change of neutralisation of sodium hydroxide by an acid and also the concentration of hydrogen ions in the acid. These can be found by measuring the temperature change when solutions of the acid and alkali are mixed. FB 1 is 1.50 mol dm–3 sodium hydroxide, NaOH. FB 2 is an aqueous solution of an acid. (a) Method • Fill a burette with FB 1. [Care: FA1 is corrosive] • Support the plastic cup in a 250 cm3 beaker. • Run 10.0 cm3 of FB 1 from the burette into the plastic cup. • Measure and record, in the table below, the temperature of the FB 1 in the cup. You may need to tilt the beaker to ensure that the bulb of the thermometer is covered. • Measure 40 cm3 of FB 2 using the measuring cylinder. • Pour this volume of FB 2 into the plastic cup containing FB 1. Stir carefully and measure the highest temperature obtained. • Record this temperature in the table. • Rinse the plastic cup with water. • Repeat the experiment using 15.0 cm3 of FB 1 and 35 cm3 of FB 2 as shown for experiment 2 in the table. • Carry out experiments 3 to 7 in the same way. • Complete the table for each experiment. Results experiment number 1 2 3 4 5 6 7 volume of FB 1 / cm3 10.0 15.0 20.0 25.0 30.0 35.0 40.0 50.0 0.0 volume of FB 2 / cm3 40 35 30 25 20 15 10 0 50 initial temperature FB 1 / °C highest temperature / °C temperature change / °C 0.0 0.0 [8] I II III IV V VI VII VIII

3 9701/34/O/N/11 © UCLES 2011 [Turn over For Examiner’s Use (b) On the grid below plot the temperature change (y-axis) against the volume of FB 1 (x-axis). Use all the results in the table including those provided in the final two columns. Using these points, draw two straight lines that intersect. [4] I II III IV

4 9701/34/O/N/11 © UCLES 2011 For Examiner’s Use (c) (i) Use your graph and the intersection of the two lines to determine the largest temperature change which could occur in the reaction between FB 1 and FB 2. largest temperature change = … °C (ii) From your graph, read the volume of FB 1 required to produce the temperature change in (i). volume of FB 1 required is = … cm3 (iii) Calculate how many moles of sodium hydroxide are present in the volume of FB 1 recorded in (ii). moles of sodium hydroxide present = … mol (iv) Use the temperature change from (i) to calculate the amount of heat energy produced in the reaction. [Assume that 4.3 J are required to raise the temperature of 1 cm3 of any solution by 1°C] heat energy produced = … J (v) Use your answers from (iii) and (iv) to calculate the enthalpy change of neutralisation of sodium hydroxide by the acid. Give your answer in kJ mol–1 and include the relevant sign. enthalpy change of neutralisation = … … kJ mol–1 sign value [7] I II III IV V VI VII

5 9701/34/O/N/11 © UCLES 2011 [Turn over For Examiner’s Use (d) Identify a source of error, other than heat loss, in the experimental method. Suggest an improvement which would reduce this source of error. … … … … [2] (e) (i) Calculate the concentration of hydrogen ions, H+, in mol dm–3, present in FB 2. concentration of hydrogen ions in FB 2 = … mol dm–3 (ii) If the acid present in FB 2 is sulfuric acid, calculate its concentration. concentration of sulfuric acid = … mol dm–3 (iii) Describe a chemical test by which you could prove that the acid in FB 2 is sulfuric acid. Do not carry out the test. … … … … [4] [Total: 25] I II III IV

6 9701/34/O/N/11 © UCLES 2011 For Examiner’s Use 2 Qualitative Analysis At each stage of any test you are to record the 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 identified 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 full name or correct formula of the reagents must be given. (a) (i) FB 3, FB 4 and FB 5 are aqueous solutions of sodium compounds. None of these compounds contains sulfur. To about 1 cm depth of each of the solutions in separate test-tubes add the same depth of dilute sulfuric acid. To another 1 cm depth of each of the solutions in separate test-tubes add a few drops of aqueous lead(II) nitrate. Record your observations for these tests in an appropriate form in the space below. I II III IV V VI

7 9701/34/O/N/11 © UCLES 2011 [Turn over For Examiner’s Use Using the Qualitative Analysis Notes printed on pages 10 and 11 and your observations identify the anions in FB 3 and FB 4. FB 3 contains … FB 4 contains … [6] (ii) Select a reagent or pair of reagents that would enable you to determine the identity of the anion in FB 5. reagent(s) … Carry out a test on FB 5 using the reagent(s) given above. Record your observations below. … … … The anion present in FB5 is … [3] I II III

8 9701/34/O/N/11 © UCLES 2011 For Examiner’s Use (b) You are provided with solid FB 6. Complete the following table. test observations (i) To 1 cm depth of aqueous hydrogen peroxide in a test-tube, add a very small spatula measure of FB 6. (ii) To 1 cm depth of aqueous iron(II) sulfate in a boiling tube, add the same depth of dilute sulfuric acid. Add a very small spatula measure of FB 6 to the tube. Warm the mixture gently using a Bunsen burner for about 20 seconds, then filter the warm mixture and collect the filtrate. To the filtrate, add aqueous sodium hydroxide. (iii) To 2 cm depth of aqueous potassium manganate(VII) in a test-tube, add the same depth of aqueous sodium hydroxide and then a small spatula measure of FB 6. Stir the contents of the test-tube for about 20 seconds. Filter the mixture and collect the filtrate. To the filtrate, add dilute sulfuric acid.

9 9701/34/O/N/11 © UCLES 2011 [Turn over For Examiner’s Use Suggest a conclusion that could be made about the chemical behaviour of FB 6 from the observations in (i). Explain the reasons for your answer. … … What conclusion can be made about the chemical behaviour of FB 6 from the observations in (ii)? … … [6] [Total: 15] I II III IV V VI

10 9701/34/O/N/11 © UCLES 2011 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.]

11 9701/34/O/N/11 © UCLES 2011 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) sulfite, 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, Cl2 bleaches damp litmus paper hydrogen, H2 “pops” with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium dichromate(VI) from orange to green

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UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2011 question paper for the guidance of teachers 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 must be read in conjunction with the question papers and the report on the examination. • Cambridge will not enter into discussions or correspondence in connection with these mark schemes. Cambridge is publishing the mark schemes for the October/November 2011 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – October/November 2011 9701 34 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark 1 (a) MMO Collection I Performs experiment and records all sensible thermometer readings. 1 PDO Collection II Records all thermometer readings to 0.0/0.5 °C. 1 ACE Interpretation III Correctly calculates the temperature rises. 1 MMO Quality Award IV, V and VI for a ∆T within 0.5 °C of Supervisor’s result. Award IV and V for a ∆T within 1.0 °C of Supervisor’s result. Award IV only for a ∆T within 1.5 °C of Supervisor’s result. 3 Calculate result for 35 cm3 by multiplying candidate’s result for 30 cm3 of FB 1 by 0.75, round up to the nearest 0.5 ºC. Award VII and VIII if candidate’s temperature rise for 35 cm3 FB 1 is within 0.5 °C of calculated value. Award VII only if ∆T is within 1.0 °C 2 [8] (b) PDO Display I Axes labelled: temperature/T change or ∆T and volume/Vol/V sodium hydroxide/NaOH and correct units /°C or (°C) or ‘in °C’, /cm3 or (cm3). 1 II Suitable scales chosen so that the points, if plotted, would occupy at least half the available length for x- and y-axes. Do not award if 50 cm3 not included. 1 III Plotting – accurate to within half a small square and in the correct square. 1 IV Draws two straight lines of best fit which intersect. Allow coming to a point (not curved). Does not have to go through (0,0). 1 [4]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – October/November 2011 9701 34 © University of Cambridge International Examinations 2011 (c) ACE Interpretation (i) I Reads to nearest ½ square temperature rise to 1 dp at point of intersection. Do not award if intersection < largest ∆T. 1 (ii) II Reads to nearest ½ square volume of FB 1 to 1 dp or nearest 0.5 cm3 at point of intersection. 1 (iii) III Correctly calculates moles of sodium hydroxide [volume of FB 1 in (ii) × 1.5/1000] to 2 to 4 sf. 1 (iv) IV Heat energy produced = 50 × 4.3 × temperature rise from (i) 1 V Correct answer calculated to 3 or 4 sf. ecf from incorrect volume 1 (v) VI ) ( to answer s candidate' ) ( to answer s candidate' iii iv 1 1 VII Negative sign and answer in kJ to 2 to 4 sf 1 [7] (d) ACE Interpretation Identifies a source of error e.g. precision of thermometer, precision of measuring cylinder* 1 ACE Improvements Suggests thermometer with smaller scale divisions (0.1°C), use of burette* 1 [2] (e) ACE Interpretation (i) I Calculates or expression for the volume of FB 2 which reacts [50 – (c)(ii)]. 1 II Correctly calculates the concentration of H+ in mol dm–3 (≥ 2 sf) [(c)(iii) × 1000/{50 – (c)(ii)}]. 1 PDO Display (ii) III Divides the answer from (i) by 2 1 Decisions (iii) IV Describes test and result for sulfate ion. White ppt with (aq) barium chloride or nitrate 1 [4] [Total: 25] 1st mark 2nd mark use more sensitive thermometer 0.5, 0,2, 0.1ºC or smaller % error smaller divisions in measuring cylinder burette or decrease % error use burette as more accurate cup has little water, use dry cup * e.g. 10 cm3 too small to take T, start with 20 cm3

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – October/November 2011 9701 34 © University of Cambridge International Examinations 2011 FB 3 is Na2CO3(aq); FB 4 is Na2CrO4(aq); FB 5 is NaBr; FB 6 is MnO2 2 (a) PDO Recording (i) I All observations in a single table (2 × 3) No repeat of headings & ≥ 4 boxes filled. 1 MMO Collection Observations for both tests on each solution are correct. II FB 3 1 III FB 4 1 IV FB 5 1 Solution H2SO4 Pb(NO3)2 FB 3 bubbling/effervescence and CO2 identified by test (allow gas turns limewater milky) white ppt FB 4 turns orange/orange (solution) forms (not ppt but not CON for identity) yellow ppt FB 5 no change/no reaction [not “ – “] white ppt ACE Conclusions V FB 3 carbonate/CO3 2– from effervescence or positive limewater test 1 VI FB 4 chromate(VI)/chromate/CrO4 2– from either observation but no CON obs 1 [6] MMO Decisions Collection (ii) I Addition of (aq) silver nitrate to FB 5. ecf on obs in table if no ppt with FB 5 + Pb2+ II Cream ppt (white ppt loses II and III) If NH3 used obs must be correct. 1 1 ACE Conclusions III FB 5 bromide/Br– from cream ppt (or off- white ppt insol or partially soluble in NH3) 1 [3] (b) MMO Collection (i) I (bubbling/effervescence and) gas rekindles glowing splint 1 (ii) II filtrate is yellow/qualified yellow/yellowish green/light brown and produces a red- brown/brown/rust/black (not red) ppt with aqueous sodium hydroxide 1 (iii) III filtrate is green/qualified green 1 IV filtrate turns purple/pink (with acid) 1 ACE Conclusions V (i) FB 6 is a catalyst Allow O2 formed or H2O2 decomposes if glowing splint test correct. 1 VI (ii) FB 6 is an oxidant/oxidising agent/is reduced. 1 [6] [Total: 15]