Cambridge A Level Chemistry 9701 — 2011 Oct/Nov Paper 3 · Variant 1

This document consists of 9 printed pages and 3 blank pages. DC (NH/JG) 35116/5 © UCLES 2011 [Turn over 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 8 and 9. 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. * 5 1 8 8 1 8 2 1 7 1 * CHEMISTRY 9701/31 Advanced Practical Skills 1 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 9701/31/O/N/11 © UCLES 2011 For Examiner’s Use 1 You are to determine the enthalpy change of neutralisation of hydrochloric acid by aqueous sodium hydroxide and also the concentration of the aqueous sodium hydroxide. These can be found by measuring the temperature change when solutions of the acid and alkali are mixed. FA 1 is aqueous sodium hydroxide, NaOH. FA 2 is 2.00 mol dm–3 hydrochloric acid, HCl. (a) Method • Fill a burette with FA 1. [Care: FA 1 is corrosive] • Support the plastic cup in a 250 cm3 beaker. • Use a measuring cylinder to transfer 25 cm3 of FA 2 into a 100 cm3 beaker. • Use a measuring cylinder to add 35 cm3 of distilled water to the acid in the beaker. • Measure and record, in the table below, the initial temperature of the mixture in the beaker. • Run 5.0 cm3 of FA 1 from the burette into the plastic cup. • Add the mixture of acid and water from the 100 cm3 beaker to the FA 1 in the plastic cup. • Stir carefully and measure the highest temperature obtained. • Record this temperature in the table. • Rinse the plastic cup with water. • Repeat the experiment using 25 cm3 of FA 2, 30 cm3 of distilled water and 10.0 cm3 of FA 1 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 FA 2 / cm3 25 25 25 25 25 25 25 volume of water / cm3 35 30 25 20 15 10 5 volume of FA 1 / cm3 5.0 10.0 15.0 20.0 25.0 30.0 35.0 initial temperature of acid mixture / °C highest temperature / °C temperature change / °C [7] I II III IV V VI VII

3 [Turn over © UCLES 2011 9701/31/O/N/11 For Examiner’s Use (b) On the grid below plot the temperature change (y-axis) against the volume of FA 1 (x-axis). Using these points, draw two straight lines that intersect. [4] I II III IV

4 9701/31/O/N/11 © UCLES 2011 For Examiner’s Use (c) Reading from the intersection of the two lines on your graph, the volume of FA 1 is … cm3, the temperature change is … °C. [1] The volume of FA 1 at the intersection represents the volume of FA 1 which neutralised 25.0 cm3 of FA 2. (d) The reaction between FA 1 and FA 2 is shown in the equation below. NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) This reaction is exothermic. Use this information to explain the shape of the graph. … … … … [2] (e) Calculate the amount of heat energy produced in the reaction. Use the temperature change from (c) in calculating your answer. [Assume that 4.3 J are required to raise the temperature of 1 cm3 of any solution by 1 °C] heat energy produced = … J [2] (f) Calculate how many moles of hydrochloric acid are present in 25 cm3 of FA 2. mol of hydrochloric acid = … [1] (g) Use your answers to (e) and (f) to calculate the enthalpy change of neutralisation of hydrochloric acid by aqueous sodium hydroxide. Give your answer in kJ mol–1 and include the relevant sign. enthalpy change of neutralisation = … … kJ mol–1 sign value [2]

5 [Turn over © UCLES 2011 9701/31/O/N/11 For Examiner’s Use (h) Explain why the total volume of solution used was kept constant in each of the experiments. … … … [1] (i) Calculate the concentration, in mol dm–3, of the aqueous sodium hydroxide, FA 1. concentration of FA 1 = … mol dm–3 [2] (j) A student thought that the experiment was not accurate because the temperature changes measured were small. Suggest a modification to the experimental method used in order to give larger changes in temperature. … … [1] (k) Experiments 1 to 7 were repeated using 1.00 mol dm–3 sulfuric acid, H2SO4, instead of the 2.00 mol dm–3 hydrochloric acid, HCl. On the axes below indicate an appropriate temperature scale and sketch the graph for the temperature changes you would expect. 0 temperature change / °C 35 volume FA 1 / cm3 [2] [Total: 25]

6 9701/31/O/N/11 © UCLES 2011 For Examiner’s Use 2 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 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) You are provided with three sodium salts FA 3, FA 4 and FA 5. Each salt contains one of the ions carbonate, CO3 2–, sulfite, SO3 2– or sulfate, SO4 2–. (i) Using your knowledge of the reactions of these ions, suggest one reagent you could add to the solid to find out which ion is present in each of the solids. … (ii) Use the reagent you selected in (i) to identify which of these ions is present in FA 3, FA 4 and FA 5. Carry out suitable tests on a small amount of each solid and record the results of your experiments in an appropriate form in the space below. Identify the anions in FA 3, FA 4 and FA 5. FA 3 contains the … ion. FA 4 contains the … ion. FA 5 contains the … ion. [6] I II III IV V VI

7 [Turn over © UCLES 2011 9701/31/O/N/11 For Examiner’s Use (b) (i) You are provided with FA 6 both as a solid and in aqueous solution. Complete the following table. test observations To a small spatula measure of FA 4 in a test-tube, add enough distilled water to make a solution. Add 1 cm depth of FA 6 solution. To a small spatula measure of FA 5 in a test-tube, add enough distilled water to make a solution. Add 1 cm depth of FA 6 solution. To 1 cm depth of FA 6 solution in a test-tube, add aqueous sodium hydroxide. Carefully heat the solid FA 6 in the test-tube provided. Note: two gases are released. [6] (ii) From the results of the tests in (i), identify the cation present in FA 6. Cation present in FA 6 is ……………………….. [1] (iii) Suggest and use another reagent to confirm the cation present in FA 6. reagent … observation …[2] [Total: 15] I II III IV V VI

8 9701/31/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.]

9 9701/31/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

10 9701/31/O/N/11 © UCLES 2011 BLANK PAGE

11 9701/31/O/N/11 © UCLES 2011 BLANK PAGE

12 9701/31/O/N/11 © UCLES 2011 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. 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.

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 9701/31 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 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 31 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark 1 (a) PDO Recording I Thermometer readings for all experiments recorded to 0.0 or 0.5°C. (At least one recorded to 0.5°C.) 1 ACE Interpretation II Calculation of all temperature changes correct. 1 MMO Quality Award III for a temperature rise followed by constant temperature (within 0.5°C). 1 Award IV and V for a maximum rise within 0.5°C of supervisor. 1 Award IV for a maximum rise within 1.0°C of supervisor. 1 Award VI and VII for the experiment 3 temperature rise within 0.5°C of supervisor. 1 Award VI for the experiment 3 temperature rise within 1.0°C of supervisor. 1 [7] (b) PDO Layout I Axes correct and labelled: temperature change/ T change/∆T and volume/vol/V (of) sodium hydroxide/NaOH/FA 1 and correct units /°C or (°C) or ‘in °C’; /cm3 or (cm3) (allow NaOH in cm3) 1 II Scales chosen so that graph occupies at least half the available length for x- and y-axes. 1 III Plotting – all points accurate to within half a small square and in the correct square. 1 IV Draws two straight lines of best fit which intersect. 1 [4] (c) ACE Interpretation Reads to nearest ½ square to 1 or 2 dp volume of FA 1 and temperature rise from intercept. Do not award if ∆T at intercept (or point) < max ∆T from table unless candidate has clearly indicated the max ∆T is anomalous. 1 [1]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – October/November 2011 9701 31 © University of Cambridge International Examinations 2011 (d) ACE Conclusions I The temperature/temperature change increases as more reaction/more hydrochloric acid/sodium hydroxide reacts/as more water formed. 1 II The temperature/temperature change stays constant/decreases when all acid/limiting reagent has reacted/excess NaOH is added. 1 [2] (e) ACE Interpretation I Volume used in calculation is 65 cm3 1 II Heat energy change calculated using candidate’s value for ∆T correct to 3 or 4 sf 1 [2] (f) ACE Interpretation 25 × 2 = 0.05 1000 1 [1] (g) ACE Interpretation I Candidate’s answer to (e) Candidate’s answer to (f) 1 PDO Display II Correct calculation, conversion J to kJ and negative sign to 3 or 4 sf 1 [2] (h) ACE Conclusions So that rise in temperature is proportional to increase in energy produced/change in volume gives different change in temperature for same energy produced/ increase in volume requires increase in energy for same temperature rise. 1 [1] (i) PDO Display I Number moles NaOH = number moles HCl (stated or clearly shown) 1 ACE Interpretation II Calculates or expression for Concentration = 0.05 (ecf from (f)) answer to (c)/1000 If answer only, award mark if correct to 3 or 4 sf 1 [2] (j) ACE Improvements Use more concentrated solutions. (allow use ≤ 5 cm3 water each time) Ignore all references to heat energy losses. 1 [1] (k) ACE Conclusions I Two straight intersecting lines (positive followed by zero gradient). 1 II Same ∆T and V shown as in (b). 1 [2] [Total: 25]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – October/November 2011 9701 31 © University of Cambridge International Examinations 2011 FA 3 is Na2S2O5(s); FA 4 is Na2CO3(s); FA 5 is Na2SO4(s); FA 6 is Pb(NO3)2(s) and (aq) 2 (a) MMO Decisions (i) I Any named mineral acid or formula or (acidified) potassium dichromate Do not allow any reagent suitable for testing cations or more than one reagent. 1 PDO Recording (ii) II Tabulates evidence of 3 tests carried out with no repeat headings. Only consider observations with acid or dichromate. 1 MMO Collection III Bubbles/effervescence in FA 4. 1 IV Slower effervescence in FA 3 than FA 4 or FA 3 turns green and FA 5 stays orange if dichromate used. 1 MMO Decisions V Appropriate test with positive result used to test for either gas. 1 ACE Conclusions VI All three ions correct from suitable observations. FA3 is a sulfite. FA4 is a carbonate. FA5 is a sulfate. (or correct formulae) 1 [6] (b) MMO Collection (i) I FA 4 + FA 6 white ppt and FA 5 + FA 6 white ppt. 1 II FA 6 + NaOH white ppt, soluble in excess sodium hydroxide. III Brown gas IV Gas relights glowing splint. V Yellow residue or crackling/decrepitating. ACE Conclusions VI Gas identified as oxygen or as NO2 from observations. [6] ACE Conclusions (ii) Lead/Pb2+ provided correct observations with FA 6 + NaOH and FA 6 + FA 5 (sulfate). 1 [1] MMO Decisions (iii) I Add HCl / H2SO4 / KI / K2CrO4 / NH3* 1 MMO Collection II white ppt/white ppt/yellow ppt/yellow ppt/white ppt insoluble in excess. 1 * If not Pb2+ in (ii) but one of Al3+, Ba2+, Ca2+, Zn2+ allow suitable reagent mark: K2CrO4 for Ba2+ and NH3 for the other three. However, observation must be correct for Pb2+. [2] [Total: 15]