Cambridge A Level Chemistry 9701 — 2013 May/June Paper 3 · Variant 2

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. 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 9701/32 Advanced Practical Skills 2 May/June 2013 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 11 printed pages and 1 blank page. [Turn over IB13 06_9701_32/4RP © UCLES 2013 *0257891118* Session Laboratory For Examiner’s Use 1 2 Total

2 9701/32/M/J/13 © UCLES 2013 For Examiner’s Use I II III IV V 1 You will determine the enthalpy change, ∆H, for the reaction of sodium carbonate, Na2CO3, with water and carbon dioxide to form sodium hydrogencarbonate, NaHCO3. In step 1 you will react a known mass of sodium hydrogencarbonate with a known volume of dilute hydrochloric acid and fi nd the temperature change. In step 2 you will fi nd the temperature change on adding a known mass of sodium carbonate to a known volume of acid. You will then use your results to calculate the enthalpy change for the reaction. Na2CO3(s) + H2O(l) + CO2(g) → 2NaHCO3(s) FB 1 is sodium hydrogencarbonate, NaHCO3. FB 2 is sodium carbonate, Na2CO3. FB 3 is 2.0 mol dm–3 hydrochloric acid, HCl. (a) Method Step 1 NaHCO3(s) + HCl (aq) → NaCl (aq) + H2O(l) + CO2(g) ● Place the plastic cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25 cm3 of the acid, FB 3, into the plastic cup. The acid is in excess. ● Weigh the container with FB 1 and record the balance reading in a suitable form below. ● Place the thermometer in the acid and record the initial temperature in the table of results. Tilt the cup if necessary so that the bulb of the thermometer is fully covered. This is the temperature at time zero. Start timing. ● Record the temperature of the acid at 1 minute and at 2 minutes. ● At 2½ minutes carefully tip all the FB 1, in small portions to avoid spray, into the acid and stir to dissolve it. ● Record the temperature of the solution at 3, 4, 5, 6, 7 and 8 minutes. ● Reweigh the container with any residual FB 1 and record the balance reading and the mass of FB 1 used. ● Rinse out the plastic cup and shake it to remove excess water. Results Mass Temperature Time in minutes 0 1 2 3 4 5 6 7 8 Temperature / °C [5]

3 9701/32/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use I II III IV (b) Plot temperature on the y-axis against time on the x-axis on the grid below. You will use the graph to determine the theoretical temperature change at 2½ minutes. The scale for temperature should extend at least 1 °C below your lowest recorded temperature. Draw two straight lines of best fi t on your graph, one for the temperature of the acid before adding FB 1 and the other for the warming of the solution once the reaction is complete. Extrapolate the two lines to 2½ minutes and determine the change in temperature at this time. temperature change at 2½ minutes = … °C [4]

4 9701/32/M/J/13 © UCLES 2013 For Examiner’s Use (c) Method Step 2 Na2CO3(s) + 2HCl (aq) → 2NaCl (aq) + H2O(l) + CO2(g) ● Read through the method and prepare a suitable table for your results. ● Place the plastic cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25 cm3 of the acid, FB 3, into the plastic cup. The acid is in excess. ● Weigh the container with FB 2 and record the balance reading. ● Place the thermometer in the acid and record the initial temperature. Tilt the cup if necessary so that the bulb of the thermometer is fully covered. ● Carefully tip all the FB 2, in small portions to avoid spray, into the acid and stir to dissolve it. ● Record the highest temperature. ● Reweigh the container with any residual FB 2 and record the balance reading and the mass of FB 2 used. Results [3] (d) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Using your answer to (b), calculate the heat energy absorbed when FB 1 was added to the acid in step 1. (Assume that 4.3 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 °C.) heat energy absorbed = … J I II III

5 9701/32/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use (ii) Calculate the enthalpy change, in kJ mol–1, when 1 mole of FB 1, NaHCO3, reacts with acid. (Ar: H, 1.0; C, 12.0; O, 16.0; Na, 23.0) enthalpy change = … … kJ mol–1 (sign) (value) (iii) Using your results from (c), calculate the heat energy produced when FB 2 was added to the acid in step 2. (Assume that 4.3 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 °C.) heat energy produced = … J (iv) Calculate the enthalpy change, in kJ mol–1, when 1 mole of FB 2, Na2CO3, reacts with acid. (Ar: C, 12.0; O, 16.0; Na, 23.0) enthalpy change = … … kJ mol–1 (sign) (value) (v) Use your answers to parts (ii) and (iv) and the equations for steps 1 and 2 to determine the enthalpy change for the reaction below. Na2CO3(s) + H2O(l) + CO2(g) → 2NaHCO3(s) enthalpy change, ∆H = … … kJ mol–1 (sign) (value) [7] I II III IV V VI VII

6 9701/32/M/J/13 © UCLES 2013 For Examiner’s Use (e) (i) Complete the following table. The balance used in the experiment reads to … decimal place(s). The maximum error in a single balance reading is … g. The maximum error in measuring the recorded mass of FB 2 in (c) would be … g. (ii) Calculate the maximum percentage error in the mass of FB 2 in step 2. maximum percentage error in the mass of FB 2 in step 2 = … % [2] (f) (i) A student stated that the experiment could be made more accurate by using twice the volume of acid in step 1 and step 2. Suggest whether the student is correct or incorrect and justify your answer. The student is … because … … … [1] (ii) Another student carried out step 2 twice using the carbonate of a different metal and obtained the following results. First result: mass used = 2.96 g; increase in temperature = 4.0 °C Second result: mass used = 3.65 g; increase in temperature = 5.0 °C The student then used the mean mass and the mean temperature increase when calculating the enthalpy change for the reaction. Explain whether or not the student was justifi ed in using the results in this way, by showing appropriate calculations. … … … … [2] [Total: 24]

7 9701/32/M/J/13 © UCLES 2013 [Turn over 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 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, FB 5 and FB 6 are aqueous solutions of salts. Each contains a different anion which is either sulfate, chloride or nitrate. Using the Qualitative Analysis Notes on page 11, select reagents to allow you to identify positively which anion is in each salt using the minimum number of tests. Record your reagents and your observations in the table below. Indicate where a test is unnecessary using a dash, —. reagent(s) FB 4 FB 5 FB 6 [5] I II III IV V

8 9701/32/M/J/13 © UCLES 2013 For Examiner’s Use (b) Many cations are identifi ed by using aqueous sodium hydroxide and aqueous ammonia in small amounts and then to excess. Carry out the following tests and record all your observations in the table provided below. test observations FB 4 FB 5 FB 6 (i) To 1 cm depth of salt solution in a test-tube, add a few drops of aqueous sodium hydroxide, then add excess. (ii) To 1 cm depth of salt solution in a test-tube, add a few drops of aqueous ammonia, then add excess. [3] (c) From your observations in (a) and (b), identify as many of the ions present as possible. FB 4 FB 5 FB 6 cation anion [3]

9 9701/32/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use (d) One or more of the solutions contain(s) a second cation, the hydrogen ion, H+. (i) State two tests that can be used to show whether H+ is present. test 1 … test 2 … (ii) Carry out your tests and record your observations in a suitable form in the space below. (iii) Identify which of the solutions FB 4, FB 5 and FB 6 contain(s) the hydrogen ion, H+. H+ is present in … . [5] [Total: 16] I II III IV V

10 9701/32/M/J/13 © UCLES 2013 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 9701/32/M/J/13 © UCLES 2013 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

12 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. 9701/32/M/J/13 © UCLES 2013 BLANK PAGE

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2013 series 9701 CHEMISTRY 9701/32 Paper 32 (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 2013 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 – May/June 2013 9701 32 © Cambridge International Examinations 2013 Question Sections Indicative material Mark 1 (a) MMO Collection I All thermometer readings and two weighings + correct mass of FB 1 recorded. 1 PDO Recording II Correct headings and units in table (lines not needed). Weighings and mass to same no. dp. Must use solidus, brackets or describe unit fully in words. If units not included in column headings, every entry must have the correct unit shown. 1 III Temperature recorded to 0.5 ºC (must have at least one ending in .5 ºC and one ending in .0 °C). 1 MMO Quality Award IV and V if δ ≤ 0.30 °C g–1 Award IV if 0.30 < δ ≤ 0.60 °C g–1 1 1 [5] 1 (b) PDO Layout I Uniform scales chosen to use more than half of each axis. At least 5 large squares on y-axis. Axes labelled, units not needed. Scale extends at least 1 °C below lowest recorded point. 1 II All points correctly plotted to within ½ small square and in correct small square. 1 III Appropriate lines of best fit drawn. 1 ACE Interpretation IV Lines extrapolated and correct value (within 0 .5 oC) of ∆T from graph (ignore sf and sign). 1 [4] 1 (c) PDO Recording I Table drawn to include weighings, correct mass of FB 2, initial and final thermometer readings (ignore units), headings must be unambiguous. 1 MMO Quality Award II and III if δ ≤ 0.30 °C g–1 Award II if 0.30 < δ ≤ 0.60 °C g–1 1 1 [3]

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 32 © Cambridge International Examinations 2013 (d) (i) (iii) (ii) PDO Display I Shows 25 x 4.3 × ∆T for step 1 and for step 2 (no need to check calculation). II Should be
  . 
    1 (iv) III Calculates
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    1 1 (v) ACE Conclusions Award IV and V if correctly calculates ∆H from answers to (ii) and (iv) with correct sign (answer to (iv) – 2 × answer to (ii) scores 2 (iv) – (ii) scores 1 2(ii) – (iv) scores 1) 1 PDO Display VI Signs in (ii) (+ve) and (iv) (–ve). 1 VII All final answers given to 2 or 4 sf (minimum of 3 answers attempted). 1 [7] (e) (i) ACE Interpretation Single balance reading ± 0.005 or 0.01 g for 2dp balance. ∆m ± 0.01 or 0.02 g for 2 dp balance. 0.05 or 0.1 g for 1 dp balance / 0.0005 or 0.001 for 3 dp. 1 (ii) Number of dps must correspond to candidate’s own readings. Calculates max ∆m error / mass FB 2 in Step 2 to 2 or more sf (2 minimum for 1 dp balance and up to 4 for 3 dp balance). Allow ecf. 1 [2] (f) (i) ACE Improvements Student incorrect as acid already in excess/ greater volume gives smaller ∆T/greater volume needs more heat energy and/or greater % error. 1 [1] (ii) MMO Interpretation Attempts to calculate ∆T / m or m / ∆T for each result or ratios of m1/m2 and T1 / T2 or similar (not averages of two). 1 MMO Decisions Correct calculation (1.35 / 1.37 or 0.74 / 0.73). Conclusion – yes, values concordant / consistent or no, values differ. 1 [2] [Total: 24]

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 32 © Cambridge International Examinations 2013 FB 4 MnCl2 FB 5 Fe(NO3)3 + HNO3 FB 6 ZnSO4 + H2SO4 2 (a) MMO Decisions I Selects any 2 from barium chloride or nitrate, silver nitrate or lead nitrate. 1 II NaOH (allow OH if ion formulae already penalised) + Al and warm for NO3 –. 1 For III and IV any two from MMO Collection • only FB 4 gives white ppt with Ag+ • only FB 6 gives white ppt with Ba2+ • FB 4 and FB 6 give a white ppt with Pb2+ (allow relevant dash as alternative to ppt) 1 1 1 [5] (ppt in any other test with Ag+, Pb2+ or Ba2+ is a CON) V FB 5 only forms gas/ NH3 turns litmus paper blue 2 (b) MMO Collection FB 4 gives off-white / buff / light brown ppt insoluble in both and darkening of the ppt in either. 1 FB 5 gives red-brown/brown/rust/orange-brown (not red, not orange) ppt insoluble in excess of both. 1 FB 6 gives white ppt soluble in excess of both or Award 1 mark if all NaOH or NH3 observations, including in excess, are correct except ‘darkening of ppt in (i). 1 [3] 2 (c) ACE Conclusions FB 4 contains Mn2+ and Cl –. FB 5 contains Fe3+ and NO3 –. FB 6 contains Zn2+ and SO4 2–. 1 1 1[3] 2 (d) MMO Decisions I Selects suitable tests: two of Mg / Zn / Fe / Na2CO3, litmus paper/U.I. paper, chromate. (specific names of reagents not needed) (expected results not needed) 1 PDO Layout II Single table (no repeat headings)(must be the 2 reagents stated above). 1 MMO Collection III Correct observations for FB 4 and either FB 5 or FB 6. For FB 4 correct observation is allowed if no +ve test for gas. 1 IV Correct observations for other from FB 5 and FB 6. 1 ACE Conclusions V FB 5 and FB 6 contain H+. 1 [5] [Total: 16]