Cambridge A Level Chemistry 9701 — 2014 Oct/Nov Paper 3 · Variant 1

This document consists of 13 printed pages and 3 blank pages. [Turn over IB14 11_9701_31/FP © UCLES 2014 *5981348564* Session Laboratory For Examiner’s Use 1 2 Total 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 14 and 15. 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 9701/31 Paper 3 Advanced Practical Skills 1 October/November 2014 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

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3 9701/31/O/N/14 © UCLES 2014 [Turn over 1 You are to determine the enthalpy change of reaction, ∆H, for the reaction shown below. Cu(s) + H2SO4(aq) → CuSO4(aq) + H2(g) Since copper is an unreactive metal it does not react directly with dilute acids. You will therefore need to fi nd the enthalpy change of reaction for two reactions that do occur. The equations for these two reactions are below. Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g) Reaction 1 Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s) Reaction 2 You will carry out experiments to fi nd the enthalpy changes for each of Reaction 1 and Reaction 2 and use these values to calculate the enthalpy change for the reaction of copper with sulfuric acid. TURN OVER FOR EXPERIMENTAL METHOD

4 9701/31/O/N/14 © UCLES 2014 Determining the enthalpy change for Reaction 1 Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g) Reaction 1 (a) Method FA 1 is 1.00 mol dm–3 sulfuric acid, H2SO4. FA 2 is magnesium powder, Mg. Read through the method before you start any practical work and prepare a suitable table for your results. ● Weigh the stoppered tube containing FA 2. Record the mass. ● Support the plastic cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25 cm3 of FA 1 into the plastic cup. ● Measure the temperature of FA 1 in the plastic cup and start the stop clock. Record this temperature as being the temperature at time = 0. ● Measure, and record, the temperature of this FA 1 every half minute for 2 minutes. ● At time = 2 2 1 minutes add the FA 2 to the acid and stir carefully to reduce acid spray. ● Measure the temperature of the mixture in the cup at time = 3 minutes and then every half minute up to time = 7 minutes. ● Continue stirring occasionally throughout this time. ● Weigh the stoppered tube that had contained FA 2. Record the mass. ● Calculate and record the mass of FA 2 added to the sulfuric acid. ● Rinse the plastic cup with water and shake to dry. [6] I II III IV V VI

5 9701/31/O/N/14 © UCLES 2014 [Turn over (b) (i) On the grid below plot a graph of temperature (y-axis) against time (x-axis). (ii) Complete the graph by inserting two, straight lines of best fi t: ● one to show the temperature up to time = 2 2 1 minutes, ● one to show the temperature after time = 2 2 1 minutes. I II III IV

6 9701/31/O/N/14 © UCLES 2014 (iii) From your graph, use the two straight lines of best fi t to calculate the change in temperature at time = 2 2 1 minutes. temperature change = … °C [4] (c) Calculations (i) In the reaction in (a), the sulfuric acid was in excess. Without carrying out any additional tests, what observation could you have made during your experiment to confi rm this? … … (ii) Calculate the energy change that occurred during the reaction in (a). [Assume that 4.2 J is needed to raise the temperature of 1.0 cm3 of solution by 1.0 °C.] energy change = … J (iii) Use your answer to (ii) to calculate the enthalpy change, in kJ mol–1, for the reaction between sulfuric acid and magnesium. [Ar : Mg, 24.3] Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g) Reaction 1 enthalpy change for Reaction 1 = … … kJ mol–1 sign value [4]

7 9701/31/O/N/14 © UCLES 2014 [Turn over Determining the enthalpy change for Reaction 2 Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s) Reaction 2 (d) Method FA 3 is 1.00 mol dm–3 copper(II) sulfate, CuSO4. FA 4 and FA 5 are magnesium powder, Mg. Read through the method before you start any practical work and prepare a suitable table for your results. ● Weigh the stoppered tube containing FA 4. Record the mass. ● Support the plastic cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25 cm3 of FA 3 into the plastic cup. ● Measure the temperature of FA 3 in the plastic cup and record the temperature. ● Add the FA 4 to the FA 3 in the cup and stir the mixture constantly. ● Measure and record the maximum temperature reached during the reaction. ● Calculate and record the maximum temperature change that occurred during the reaction. ● Weigh the stoppered tube that had contained FA 4. Record the mass. ● Calculate and record the mass of FA 4 added to the copper(II) sulfate. ● Empty the contents of the plastic cup into the 100 cm3 beaker labelled waste. ● Rinse the plastic cup and shake to dry. ● Repeat this experiment using FA 5 in place of FA 4. [2]

8 9701/31/O/N/14 © UCLES 2014 (e) Calculations (i) Using your results from (d), calculate the mean temperature rise. mean temperature rise = … °C (ii) Using your results from (d), calculate the mean mass of magnesium used. mean mass = … g (iii) Show, using a suitable calculation, that the copper(II) sulfate was in excess in these reactions. (iv) Using your values from (i) and (ii), calculate the enthalpy change, in kJ mol–1, for the reaction between magnesium and copper(II) sulfate. [Assume that 4.2 J is needed to raise the temperature of 1.0 cm3 of solution by 1.0 °C.] [Ar : Mg, 24.3] Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s) Reaction 2 enthalpy change for Reaction 2 = … … kJ mol–1 sign value [4]

9 9701/31/O/N/14 © UCLES 2014 [Turn over Enthalpy change for Reaction 3 Reaction 3 is shown below. Cu(s) + H2SO4(aq) → CuSO4(aq) + H2(g) Reaction 3 (f) Use your values for the enthalpy changes for Reactions 1 and 2 to calculate the enthalpy change for Reaction 3. Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g) Reaction 1 Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s) Reaction 2 Show clearly how you obtained your answer. (If you were unable to calculate the enthalpy changes for Reactions 1 and 2, you should assume that the value for Reaction 1 is – 444 kJ mol–1 and that the value for Reaction 2 is – 504 kJ mol–1. Note: these are not the correct values.) enthalpy change for Reaction 3 = … … kJ mol–1 sign value [2] (g) (i) The method you used to determine the enthalpy change for Reaction 1 was more accurate than the method you used to determine the enthalpy change for Reaction 2. Suggest two reasons why the method used for Reaction 2 was less accurate. Explain your answers. 1 … … … 2 … … … (ii) A student suggested that the accuracy of the method used for Reaction 2 could be improved by using a larger volume of copper(II) sulfate. Is this a correct suggestion? Give a reason for your answer. … … [3] [Total: 25]

10 9701/31/O/N/14 © UCLES 2014 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 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) FA 6 is a solid that contains one cation and one anion. One of the ions present is included in the lists on pages 14 and 15. This ion contains the element nitrogen. (i) State which nitrogen-containing ions could be present. Select reagents for use in tests that would distinguish between them. … … … (ii) Carry out tests on FA 6 using the reagents selected in (i) to identify the nitrogen-containing ion. Record your tests and observations in the space below.

11 9701/31/O/N/14 © UCLES 2014 [Turn over (iii) Identify the nitrogen-containing ion in FA 6. Ion present is … [5] (b) Half fi ll the 250 cm3 beaker with water and heat the water to about 60 °C. This is the water bath to be used in one of the following tests. Carry out the following tests on FA 7 and complete the table below. test observations To a 1 cm depth of FA 7 in a test-tube, add a few drops of dilute hydrochloric acid. To a 1 cm depth of FA 7 in a test-tube, add a few drops of aqueous potassium iodide, then add aqueous ammonia. To a 1 cm depth of FA 7 in a test-tube, add a few drops of aqueous sodium hydroxide and then add aqueous ammonia dropwise, with gentle shaking, until the precipitate just dissolves, then No observation required. add one spatula measure of glucose and leave to stand in the hot water bath. When you have completed this test, dispose of the solution and rinse the test-tube. [4]

12 9701/31/O/N/14 © UCLES 2014 (c) Solid FA 8 contains one cation and one anion from those included in the lists on pages 14 and 15. Carry out the following tests on FA 8. For each test record your observations. (i) In a hard-glass test-tube heat approximately half of the FA 8, gently at fi rst and then more strongly. Leave to cool. … … … (ii) To a 2 cm depth of dilute nitric acid in a boiling tube, add the remaining FA 8. Keep the solution obtained for tests (iii) and (iv). … … … (iii) To a 1 cm depth of the solution from (ii) in a test-tube, add aqueous sodium hydroxide until no further change occurs. … … … (iv) To a 1 cm depth of the solution from (ii) in a test-tube, add aqueous ammonia until no further change occurs. … … … (v) Use your observations from (i) to (iv) to identify the ions present in FA 8. Ions present … and … [6] [Total: 15]

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14 9701/31/O/N/14 © UCLES 2014 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

15 9701/31/O/N/14 © UCLES 2014 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

16 9701/31/O/N/14 © UCLES 2014 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. 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. BLANK PAGE

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 2014 series 9701 CHEMISTRY 9701/31 Paper 3 (Advanced Practical Skill 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 2014 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 – October/November 2014 9701 31 © Cambridge International Examinations 2014 Question Indicative material Mark Total 1 (a) I Two balance readings and correct mass of magnesium recorded. Table to show temperature and time. Headings and units – must be temperature /°C, (°C), in °C and time/s, (s), or time in seconds or /min, /minutes, ... and /g, (g), ... 1 II Thermometer readings to ±0.5 °C (at least 1 ending in .5 or .0) (Minimum 8 readings) 1 III All specified readings taken and balance readings to the same number of dp 1 Difference between temperature at 2 minutes and highest temperature (in table) calculated and compared with ∆T of Supervisor. IV, V and VI ∆T within 10% of Supervisor IVand V ∆T within 15% of Supervisor IV only ∆T within 20% of Supervisor 3 [6] (b) (i) I Axes labelled, linear scales chosen so that more than half the available space is used on both axes for plotted points. 1 II Plotted points should be drawn clearly with a sharp pencil. Points should be plotted to within half a small square and in the correct square for y-axis and on line for x-axis. 1 (ii) III Correctly extrapolated best fit straight lines drawn up to time 2½ minutes and after 2½ minutes. 1 (iii) IV Examiner calculates ∆T from graph and checks answer is within 0.25 °C of candidate’s stated answer 1 [4] (c) (i) All the magnesium / solid dissolved / disappeared or all solid / Mg has gone / been used up or no solid / Mg left 1 (ii) Correctly calculates 25 × 4.2 × ∆T 1 (iii) Correctly calculates (ii) ÷ number of moles of magnesium and converts to kJ ( Mg mass 1000 24.3 × × (ii) ) and final answer to 2–4 sf 1 Sign is negative in (c)(iii) and (e)(iv) 1 [4] (d) 8 readings (in space below printed area) • 4 × balance readings • 2 × initial temp • 2 × highest / max temp with unambiguous headings 1 Correctly calculates both masses of Mg and both ∆Ts. 1 [2]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2014 9701 31 © Cambridge International Examinations 2014 Question Indicative material Mark Total (e) (i) & (ii) Correctly calculates • mean ∆T • mean mass 1 (iii) Moles CuSO4 = 1000 1 25× = 0.025 Moles Mg = 24.3 Mg mass max or (ii) so CuSO4 in excess or <0.025 1 1 (iv) Working to calculate ∆H using mean values of mass Mg and ∆T       × × × × 1000 24.3 4.2 25 T (ii) (i) ∆ or       × × × 1000 from Mg mol 4.2 25 T (iii) (i) ∆ 1 [4] (f) Attempt at use of Hess’ law either by cycle or reverse reaction 2 1 Correctly calculates ∆H reaction 3 = ∆H reaction 1 – ∆H reaction 2 1 [2] (g) (i) Any 2 of Lower ∆H and so higher % error No correction made for loss of heat on cooling Some bubbles / gas / H2 in reaction 2 so wrong reaction taking place Not all Mg reacts / reaction does not go to completion in 2 (so not all energy released) Reaction 2 slower so more heat loss 1 1 (ii) No, since (larger volume of solution means) smaller ∆T OR Yes, since there would be a smaller T rise so less heat would be lost. 1 [3] Qn 1 Total [25]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2014 9701 31 © Cambridge International Examinations 2014 Question Indicative material Mark Total FA 6 is NaNO3(s); FA 7 is AgNO3(aq); FA 8 is ZnCO3(s) 2 (a) (i) Chooses NaOH(aq) (+ heat) (to distinguish NH4 + / ammonium) Chooses named (allow name from (ii)) dilute acid / (acidified) KMnO4 (to distinguish between NO2 – / nitrite and NO3 – / nitrate) 2 ions chosen: NH4 + & NO3 – : NaOH (and warm) NO2 – & NO3 – : named (dilute) acid NH4 + & NO2 – : either of the above 1 1 (ii) Correct obs with relevant tests With NaOH and warming / heating: no ammonia / no change / no reaction With acid(aq): no brown fumes / no change / no reaction ‘No observation’ is not credited anywhere in the observations. 1 1 (iii) FA 6 contains NO3 – (with sufficient obs to eliminate other ion(s) given in (i)) 1 [5] (b) + HCl (aq): white ppt 1 + KI: yellow ppt + NH3: no effect / ppt insol 1 1 + glucose: silver mirror / black / (dark) grey ppt 1 [4] (c) (i) (Solid is) yellow when heated Goes white / paler on cooling 1 1 (ii) effervescence / fizzing / rapid bubbling and limewater turns milky 1 (iii) White ppt and soluble in excess NaOH 1 (iv) White ppt and soluble in excess NH3 1 (v) Ions present: Zn2+ and CO3 2– (from fizz or limewater test correct) 1 [6] Qn 2 Total [15]