Cambridge A Level Chemistry 9701 — 2009 Oct/Nov Paper 3 · Variant 1

This document consists of 11 printed pages and 1 blank page. SJF4880/SJF 17555/2 © UCLES 2009 [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 are advised to show all working in calculations. 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. * 5 0 1 4 4 9 2 6 8 9 * CHEMISTRY 9701/31 Paper 31 Advanced Practical Skills October/November 2009 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions For Examiner’s Use 1 2 Total Session Laboratory

2 9701/31/O/N/09 © UCLES 2009 BLANK PAGE

3 9701/31/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use 1 You are provided with the following reagents. • two weighing bottles labelled FA 1, each containing between 2.90g and 3.00g of zinc powder • FA 2, 0.80moldm–3 copper sulfate, CuSO4 You are to determine the enthalpy change, ∆H, for the following reaction. Zn(s) + CuSO4(aq) Cu(s) + ZnSO4(aq) You will carry out the experimental procedure twice. Read through the instructions below before starting the experiment. (a) You will weigh each bottle and later in the experiment weigh it again after the zinc powder has been tipped into copper sulfate solution. In the space below prepare a table to record the weighings and the mass of zinc powder used in each experiment. Weigh accurately, to at least one decimal place, one of the weighing bottles labelled FA 1. Record this mass in the table you have prepared. [1] (b) Procedure • Support the plastic cup in the 250cm3 beaker and, using a pipette, place 25.0cm3 of FA 2 into the plastic cup. • Stir gently, taking a temperature reading every ½ minute until a steady temperature has been obtained for a period of at least 2 minutes. You may need to tilt the beaker in order to cover the bulb of the thermometer with solution. • On a precise minute reading tip the zinc powder from the weighing bottle into the plastic cup. Do not read the temperature at this time or at the following ½ minute. • Continue to stir the mixture thoroughly. Starting 1 minute after the addition of the zinc powder, record the temperature every ½ minute until the temperature has reached a maximum value and then decreased steadily for at least 5 minutes. • Reweigh the empty weighing bottle. Record the mass of the bottle + any residual zinc powder and the mass of zinc powder used in the experiment in the table you prepared in (a). • Record your results in an appropriate form in the space on the following page. Repeat the experiment using the contents of the second weighing bottle and 25.0cm3 copper sulfate solution pipetted into a clean plastic cup.

4 9701/31/O/N/09 © UCLES 2009 For Examiner’s Use (b) continued Results Make certain your readings of temperature display the precision of the apparatus used. [11] (c) Plot your temperature and time readings separately for each experiment on the grids on the next page. Your temperature axis should extend 10°C above the highest temperature you recorded. Draw lines as instructed below. On each graph draw a horizontal straight line through the steady initial temperature. Extrapolate the cooling section of each graph back to the time when you added the zinc powder. Draw construction lines on the graphs to deduce the “theoretical” temperature rise at the moment of mixing the reagents.

5 9701/31/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use experiment 1 experiment 2 [4]

6 9701/31/O/N/09 © UCLES 2009 For Examiner’s Use (d) The “theoretical” temperature rises are ……………… °C and ……………… °C. The mean “theoretical” temperature rise is ……………… °C. [1] Calculations Show working and appropriate significant figures in all of your calculations. [2] (e) Calculate how many moles of copper sulfate, CuSO4, were pipetted into the plastic cup. ……………… mol of CuSO4 were pipetted into the cup For each experiment calculate how many moles of zinc powder were added to the plastic cup. [Ar: Zn, 65.4] 1st experiment 2nd experiment In the 1st experiment ……………… mol of zinc powder were added to the plastic cup. In the 2nd experiment ……………… mol of zinc powder were added to the plastic cup. [1] (f) Use your answers to (e) and the equation for the reaction to determine which reagent was in excess and which was the limiting reagent. Explain your answer. Zn(s) + CuSO4(aq) Cu(s) + ZnSO4(aq) … … … [1]

7 9701/31/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (g) From your mean “theoretical” temperature rise at the time of mixing, calculate the heat energy released in the plastic cup by the reaction of zinc powder with copper sulfate solution. [You may assume that 4.3J are required to raise the temperature of 1cm3 of any solution by 1°C and that the mass of any solid may be ignored.] ……………… …… of heat energy are released. [1] (h) Calculate, correct to 3 significant figures, the enthalpy change in kJ mol–1 for the following reaction. Zn(s) + CuSO4(aq) Cu(s) + ZnSO4(aq) ∆H = ……………………………… kJmol–1 [2] (i) Identify and explain one source of error in the experiment you have carried out. … … … … [1] (j) Suggest a way in which the experimental method you used could be improved in a school or college laboratory in order to minimise this error. … … … … [1] [Total: 26]

8 9701/31/O/N/09 © UCLES 2009 For Examiner’s Use 2 The three boiling-tubes, labelled FA 3, FA 4, and FA 5, each contain a solid with one cation and one anion from those listed on pages 11 and 12. You will carry out specified tests to deduce the cations and anions present in FA 3, FA 4 and FA 5. 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. (a) Heat the boiling-tube containing FA 5 gently at first then more strongly. Record your observations in the space below. [2] (b) In their boiling-tubes, dissolve FA 3, FA 4 and the cold residue after heating FA 5 in a minimum of dilute nitric acid and then add distilled water so that each boiling-tube is approximately ²⁄³ full. Warm to dissolve if necessary. Record your observations in the space below. Use these solutions for tests (d), (e) and (f). [1]

9 9701/31/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (c) Which anion can be identified from your observations in (a) and (b)? Explain your answer. … … … … [1] (d) The cations present in FA 3, FA 4 and FA 5 can be identified by reaction of each solution with aqueous sodium hydroxide and with aqueous ammonia. React 1cm depth of each of the solutions prepared in (b) with each of these two reagents. Record, in an appropriate form in the space below, your observations for these reactions. Conclusions Using your observations you should be able to identify the cation present in two of the solutions. For the remaining solution you should be able to identify two possible cations. FA 3 contains the cation(s) ……………………………… . FA 4 contains the cation(s) ……………………………… . FA 5 contains the cation(s) ……………………………… . [6] i ii iii iv v vi

10 9701/31/O/N/09 © UCLES 2009 For Examiner’s Use (e) Use the information on pages 11 and 12 to select a reagent to distinguish between the two possible cations identified as present in one of the solutions in (d). Carry out the test with the selected reagent. reagent … observation … conclusion … [2] (f) Carry out the following tests. test observations FA 3 FA 4 FA 5 To 1cm depth of solution in a test- tube, add 1cm depth of aqueous barium nitrate, then add 2cm depth of dilute nitric acid. To 1cm depth of solution in a test- tube, add 1cm depth of aqueous silver nitrate, then allow any precipitate formed to settle, pour off the solution and add aqueous ammonia to the precipitate. What conclusions can be made from the observations above? … … … [2] [Total: 14]

11 9701/31/O/N/09 © UCLES 2009 [Turn over Qualitative Analysis Notes Key: [ppt. = precipitate] 1 Reactions of aqueous cations reaction with NaOH(aq) NH3(aq) aluminium, Al3+(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 9701/31/O/N/09 © UCLES 2009 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 pale 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 acid) sulfite, SO3 2– (aq) SO2 liberated with dilute acids; gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acid) 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) (aq) 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.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2009 question paper for the guidance of teachers 9701 CHEMISTRY 9701/31 Paper 31 (Advanced Practical Skills), 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. • CIE will not enter into discussions or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the October/November 2009 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 A/AS LEVEL – October/November 2009 9701 31 © UCLES 2009 Question Sections Indicative material Mark 1 (a) PDO layout Two balance readings and mass of FA 1 clearly recorded for each experiment. (Data for 2nd experiment could be on page 4) Examiner to check subtraction for each experiment – no penalty in this section but see section (e) 1 [1] PDO Recording MMO Collection If the candidate has only performed one experiment the following points only can be awarded: (ii), (iii), (vi), (vii) and (x). (i) Single table recording observations for both experiments. Times at ½ minute intervals. (ii) Appropriate headings and units Allow times in minutes (min) or seconds (iii) All temps recorded to nearest 0.5 oC (Must be more than one at .5 as well as .0) (iv) Some temps recorded before mixing and some after mixing for each expt. or Candidate records initial temperature and at least three temperatures after mixing for each experiment (v) First temperature after mixing is clearly taken 1 minute after adding the zinc powder (Examiner judgement re temperatures recorded before mixing / temperatures only recorded after mixing) and cooling for at least 5 minutes after recorded maximum temperature. 1 1 1 1 1 For Supervisor - calculate mean maximum ∆T to nearest 0.5 oC; calculate mean of time taken (to nearest ½ min) to reach max temperature after mixing. (b) MMO Quality (vi) & (vii) 1st expt. Compare ∆T with Supervisor. award (vi) and (vii) if within 2 oC award (vii) only if >2 oC and ≤5oC (viii) & (ix) 2nd expt. Compare ∆T with Supervisor. award (viii) and (ix) if within 2 oC award (ix) only if >2 oC and ≤5oC (x) (1st expt) & (xi) (2nd expt). Compare time after mixing at which max temp is obtained with same time for Supervisor, for each expt. If Supervisor ≤3 min; 1 mark for ∆ time ≤1 min. If Supervisor >3 min; 1 mark for ∆ time ≤1½ min. 2 2 1 1 [11] If the candidate performs one experiment only, the following marks may not be awarded: (i) (iv) (viii) & (ix) (xi)

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 31 © UCLES 2009 Question Sections Indicative material Mark (c) PDO Layout Plots temperature on y-axis and time on x-axis and has at least one temperature and one time label (ignore absent or incorrect units) Scales used are linear and easy for the examiner to use, (3 or 4 min. per large square are acceptable) Scales should enable the temperature when zinc is added and all points after the addition of zinc to be plotted. Points should be within a minimum of 5 large squares on temperature axis If the candidate has recorded temperatures and times before zinc is added: Correctly plots on each graph: the last temperature/time, from results before zinc is added or the temperature and maximum temperature (associated time not required If the candidate has only recorded the initial temperature of the solution: Correctly plots on each graph: the temperature when zinc is added and maximum temperature (associated time not required Draws a cooling curve or straight line and projects the curve / line back to the time of mixing 1 1 1 1 [4] (d) ACE Interpretation For experiment 1: Correctly reads the temperature rise from the graph to within 1 oC of the value obtained from the graph by the examiner. If the value is incorrect for experiment 1, check value for experiment 2. Award mark if either value is correct. 1 [1] (e)–(h) PDO Display Shows working in all sections attempted – minimum of three sections required. Significant figures in final answers. 2 or 3 sf in 1(e), 2 to 4 sf in 1(g), 3 sf only in 1(h) minimum of three sections required. 1 1 [2] (e) ACE Interpretation Correctly calculates 2.0 x 10-2 mol of CuSO4, and (mass zinc/65.4) for each experiment. Answers correctly rounded for the number of significant figures displayed. Do not award this mark if there is an error in subtraction or there are missing balance readings in section (a). 1 [1] A completely horizontal line, drawn at the initial temperature can be accepted as equivalent to plotting of initial temperature. If only one graph has been drawn, the 1st and 2nd marks may be awarded and one further mark if the initial and maximum temperatures are correctly plotted and there is an appropriate extrapolation.

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 31 © UCLES 2009 Question Sections Indicative material Mark (f) ACE Conclusions To gain this mark the candidate must refer to: (i) the 1:1 mole ratio from the equation and (ii) the relative moles of Cu2+ and Zn(s) used, as calculated in (e) If candidate states that “more moles of zinc were present” and this fits the calculated values in (e) – accept as the relative statement. 1 [1] (g) ACE Interpretation Shows (25 × 4.3 × candidate mean ∆T) with appropriate unit, J or kJ, on final answer. (Allow use of 4.2 or 4.18 without penalty) Award this mark for the correct expression and unit OR where the expression is not shown, a correct evaluation of that expression and unit 1 [1] (h) ACE Interpretation No mark is awarded in this section if there is no division by (moles of zinc) or by (moles of Cu2+). Calculates (f) in excess in being as stated not reagent of moles (g) to answer If (moles of zinc) is used in this expression, candidate may use either value from (e) or the mean of the (moles of zinc). Examiner evaluates the candidate expression which should be: (i) correctly rounded for sig fig displayed, (allow variation of ±1 on 3rd significant figure) (ii) have a -ve sign on the final answer; (iii) be correctly converted to kJ 1 1 [2] (i) ACE Interpretation Candidate identifies one source of error in the experiment. This must be related to: Apparatus used or method described – no human error allowed. Heat loss is most likely error to be seen Accept reference to the graduation (precision) of the thermometer. 1 [1] (j) ACE Improvement Answer must follow on from (i) Suggests a way in which method could be improved e.g. Use of a lid or increased insulation to minimise heat loss. 1 [1] Qn 1 Total [26] Where candidate has given a maximum temperature in (g), allow use here (ecf). Also allow use of ∆T calculated in this section.

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 31 © UCLES 2009 Question Sections Indicative material Mark FA 3 is MnSO4(s); FA 4 is PbCO3(s); FA 5 is CuCO3(s) 2 (a) MMO Collection MMO Decisions As FA 5 is heated, observes: green or blue solid turning black, or green/blue (solid) turning to a black solid or residue Tests gas given off with: Ignore results limewater, in any of a glowing (not burning) splint, these tests red litmus paper 1 1 [2] (b) MMO Collection Observes each of the following: colourless solution with FA 3 or colourless solution with FA 4, and blue or green solution with FA 5 and observation of a gas evolved with FA 4 or with FA 5. [Second mark from (a) may be awarded here if not already given in (a)] 1 [1] (c) ACE Conclusion Identifies carbonate in FA 4 or FA 5 and refers to carbon dioxide; providing there has been evidence in the tests: a positive test with limewater, or effervescence with dilute acid or Identifies carbonate in FA 4 or FA 5 and refers to specific test for carbon dioxide and its result in the conclusion. 1 [1]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 31 © UCLES 2009 Question Sections Indicative material Mark (d) PDO Recording MMO Collection ACE Conclusions (i) All observations in a single table. Both reagents are required There must be no repetition of “headings”. (ii) Reports addition of reagents to excess whenever a precipitate is formed on first addition of the reagent. (Minimum of 2 ppt) (iii) white / off-white / buff / (light or pale) brown precipitate with solution from FA 3. Precipitate insoluble in excess with both reagents and turning brown (light or pale brown precipitate darkening) recorded for at least one of the reagents (iv) Give one mark for both observations. FA 4 – white precipitate – both reagents. soluble in excess NaOH; insoluble in excess NH3(aq). and FA 5 – blue precipitate – both reagents. insoluble in excess NaOH; soluble in excess NH3(aq) or colour goes to dark/deep blue. Mark conclusions consequentially to observations. (v) Expected cations: FA 3 (Mn2+) and FA 5 (Cu2+) Minimum observations required: Mn2+ – off-white (buff, pale or light brown) ppt with each reagent but NOT from white ppt alone. Allow from white ppt turning brown. Cu2+ – blue ppt insoluble in excess NaOH or dark blue colour with aqueous NH3 (vi) Identifies Pb2+ and Al3+ as possible cations. (a single consequential ion is acceptable) 1 1 1 1 1 1 [6]

Page 7 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 31 © UCLES 2009 Question Sections Indicative material Mark (e) MMO Decisions MMO Collection If no pair of ions is given in (d), no mark can be awarded in this section Mark consequentially Selects appropriate reagent to distinguish between any pair of cations identified in (d). For Pb2+/Al3+ accept HCl, H2SO4 KI or chromate/dichromate The candidate should name a reagent, e.g. potassium dichromate. If Cr2O7 2-, or dichromate is given as the reagent the (aq) state symbol must also be given or reference made to an aqueous solution of the ions. If selected reagent is suitable; mark consequentially for chosen reagent and Pb2+. For Pb2+/Al3+ FA 4 gives white precipitate with HCl and with H2SO4 and yellow precipitate with chromate/dichromate or iodide. Ignore any conclusion. 1 1 [2] (f) MMO Collection ACE Conclusions Observes as only reaction: FA 3 gives white precipitate with Ba(NO3)2 which is insoluble in dilute nitric acid, but Ignore any white ppt or cloudiness with FA 3 and silver nitrate, and ignore cation precipitates on adding NH3(aq) Accept a dash in the boxes for reaction of FA 3, FA 4 and FA 5 with barium nitrate and with silver chloride as evidence of “no reaction” with that reagent A conclusion that fits observations for (i) barium chloride with all solutions or (ii) silver nitrate with all solutions 1 1 [2] Qn 2 Total [14]