Cambridge A Level Chemistry 9701 — 2013 Oct/Nov Paper 3 · Variant 4

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 9701/34 Advanced Practical Skills 2 October/November 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 11_9701_34/5RP © UCLES 2013 *8383886562* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/34/O/N/13 © UCLES 2013 For Examiner’s Use I II III IV V VI VII 1 FB 1 is 0.125 mol dm–3 hydrochloric acid, HCl. FB 2 is an aqueous solution containing sodium hydroxide, NaOH, and sodium carbonate, Na2CO3. bromophenol blue acid-base indicator By carrying out titrations, you are to determine the percentage by mass of sodium carbonate in the mixture of sodium hydroxide and sodium carbonate in solution FB 2. (a) Titration ● Fill a burette with FB 1. ● Pipette 25.0 cm3 of FB 2 into a conical flask. ● Add a few drops of bromophenol blue indicator. ● Titrate the mixture in the flask with FB 1 until the blue-violet colour of the solution changes to yellow. ● Perform a rough titration and record your burette readings in the space below. The rough titre is ………………. cm3. ● Carry out as many accurate titrations as you think necessary to obtain consistent results. ● Make certain any recorded results show the precision of your practical work. ● Record in a suitable form below all of your burette readings and the volume of FB 1 added in each accurate titration. [7] (b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. 25.0 cm3 of FB 2 required …………….. cm3 of FB 1 [1]

3 9701/34/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (c) Calculations When the titrations were repeated using phenolphthalein as the indicator, 25.0 cm3 of FB 2 required 23.25 cm3 of FB 1. The following explains why different results are obtained using two different indicators. ● When phenolphthalein is used as the indicator, the following reactions have taken place at the end-point of the titration. 1. NaOH(aq) + HCl (aq) → NaCl (aq) + H2O(l) 2. Na2CO3(aq) + HCl (aq) → NaCl (aq) + NaHCO3(aq) ● When bromophenol blue is used as the indicator in (a), the following reactions have taken place at the end-point of the titration. 1. NaOH(aq) + HCl (aq) → NaCl (aq) + H2O(l) 2. Na2CO3(aq) + HCl (aq) → NaCl (aq) + NaHCO3(aq) 3. NaHCO3(aq) + HCl (aq) → NaCl (aq) + CO2(g) + H2O(l) Show your working and use appropriate signifi cant fi gures in the fi nal answer to all steps of your calculations. (i) Calculate the number of moles of hydrochloric acid in the volume of FB 1 calculated in (b). moles of HCl in volume in (b) = … mol (ii) Calculate the number of moles of hydrochloric acid in 23.25 cm3 of FB 1. moles of HCl in 23.25 cm3 = … mol (iii) Use the following formula to calculate the number of moles of hydrochloric acid that react with the Na2CO3 in the titration using phenolphthalein indicator. moles HCl = answer (i) – answer (ii) = … mol

4 9701/34/O/N/13 © UCLES 2013 For Examiner’s Use I II III IV V VI (iv) Use your answer to (iii) to calculate the mass of sodium carbonate present in 25.0 cm3 of FB 2. [Ar : C, 12.0; O, 16.0; Na, 23.0] mass of Na2CO3 in 25.0 cm3 FB 2 = … g (v) The overall equation for the reaction of Na2CO3 with HCl when bromophenol blue is used as indicator is given below. Na2CO3(aq) + 2HCl (aq) → 2NaCl (aq) + CO2(g) + H2O(l) Calculate the number of moles of HCl that reacted with the Na2CO3 in the above equation in 25.0 cm3 of FB 2. moles of HCl = … mol (vi) Use your answers to (i) and (v) to calculate the mass of sodium hydroxide in 25.0 cm3 of FB 2. [Ar : H, 1.0; O, 16.0; Na, 23.0] mass of NaOH = … g (vii) Calculate the percentage by mass of sodium carbonate in the mixture of sodium hydroxide and sodium carbonate in FB 2. FB 2 contains … % by mass Na2CO3 [6] [Total: 14]

5 9701/34/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use I II III IV V VI 2 The percentage by mass of sodium carbonate in a mixture with sodium chloride can be estimated by adding a weighed sample of the mixture to a weighed excess of hydrochloric acid and measuring the mass of carbon dioxide evolved. Sodium chloride does not react with hydrochloric acid. FB 3 is 2.00 mol dm–3 hydrochloric acid, HCl. FB 4 is a mixture of solid sodium carbonate, Na2CO3, and solid sodium chloride, NaCl. You are to determine the mass of carbon dioxide given off when the sodium carbonate in the mixture, FB 4, reacts with excess hydrochloric acid. (a) Method Record all weighings, in an appropriate form, in the space below. ● Use the measuring cylinder to transfer 75 cm3 of FB 3 into a 250 cm3 conical flask. ● Weigh the flask and acid, and record the mass. ● Weigh the labelled tube containing FB 4 and record the mass. ● Tip the FB 4 into the acid in the flask, a little at a time. ● When the reaction slows down, swirl the flask for 2 to 3 minutes. Reweigh the flask and its contents, and record the mass. ● Reweigh the tube labelled FB 4 with its stopper and any residual mixture not added to the acid, and record the mass. ● Calculate the mass of the mixture, FB 4, added to the acid. ● Record the mass of carbon dioxide given off in the reaction. This may be calculated using the following formula. mass of CO2 = (mass of fl ask + acid) + (mass FB 4 added) – (fi nal mass of fl ask + contents) [6]

6 9701/34/O/N/13 © UCLES 2013 For Examiner’s Use (b) The reaction of sodium carbonate with hydrochloric acid is shown in the equation. Na2CO3(s) + 2HCl (aq) → 2NaCl (aq) + CO2(g) + H2O(l) (i) Calculate the mass of sodium carbonate that reacts with the hydrochloric acid to give the mass of carbon dioxide recorded in (a). [Ar : C, 12.0; O, 16.0; Na, 23.0] mass of Na2CO3 = … g (ii) Calculate the percentage by mass of sodium carbonate in FB 4. FB 4 contains … % by mass Na2CO3 [2] (c) Mixtures of solids containing sodium carbonate can be analysed either by the procedure you used in Question 1 or the procedure you used in Question 2. The procedure used in Question 2 is likely to give a less accurate value for the percentage of sodium carbonate. (i) Suggest a signifi cant source of error in the experimental method used in Question 2. … … (ii) State whether the error identifi ed above would increase or decrease the calculated percentage by mass of Na2CO3 in the mixture. Explain your answer. … … … (iii) Suggest an improvement to the experimental method or apparatus used in Question 2 that would reduce the error given in (i). … … [3] [Total: 11]

7 9701/34/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use 3 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) You are provided with two solids in boiling tubes labelled FB 5 and FB 6. Each solid contains one cation and one anion from those listed on pages 10 and 11. (i) Add dilute nitric acid slowly to each boiling tube until the tube is approximately one third full. Record your observations in the space below. Keep these solutions for use in (a)(ii).

8 9701/34/O/N/13 © UCLES 2013 For Examiner’s Use (ii) Use the solutions from (i) in the following tests. test observations solution from FB 5 solution from FB 6 To a 1 cm depth of solution in a test-tube add aqueous sodium hydroxide, then add excess aqueous sodium hydroxide. To a 1 cm depth of solution in a test-tube add aqueous ammonia, then add excess aqueous ammonia. To a 1 cm depth of solution in a test-tube, add aqueous potassium iodide. (iii) From your observations, identify the cations present. FB 5 contains … FB 6 contains … (iv) From your observations, what conclusions can be made about the anions present in FB 5 and FB 6? Explain your reasoning. … … … … [9]

9 9701/34/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (b) (i) Dissolve half of the solid FB 7 provided in a 4 cm depth of water in a boiling tube. Carry out the following tests and complete the table. test observations deductions about FB 7 To a 2 cm depth of the solution of FB 7 in a test-tube, add a 2 cm length of magnesium ribbon. To a 2 cm depth of the solution of FB 7 in a boiling tube, add a 1 cm depth of dilute sulfuric acid. Warm the solution and add fi ve drops of aqueous potassium manganate(VII). (ii) Tip the remaining solid FB 7 into a hard-glass test-tube. Heat the solid strongly and observe any changes. Do not test any gases given off. Record your observations in the space below. (iii) Suggest a further deduction you can make about FB 7 from your observations in (ii). … … [6] [Total: 15]

10 9701/34/O/N/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 9701/34/O/N/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. 9701/34/O/N/13 © UCLES 2013 BLANK PAGE

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2013 series 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 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 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 A LEVEL – October/November 2013 9701 34 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total 1 (a) MMO Collection I Initial and final readings and titre value given for rough titre and initial and final readings for two (or more) accurate titrations (minimum of 2 × 2 box) 1 PDO Layout II Appropriate headings and units for all accurate data and volume FB 1 added recorded for each accurate titre. Headings should match readings. • initial/start (burette) reading/volume • final/end (burette) reading/volume • titre or volume/FB 1 used/added (but not “difference”) • unit: /cm3 or (cm3) or in cm3 or cm3 for each entry 1 PDO Recording III All accurate burette readings recorded to 0.05 cm3. The need to record to 0.05 applies only to the burette readings and not to the recorded titres. Do not award this mark if: • 50(.00) is used as an initial burette reading • more than one final burette reading is 50.(00) • any burette reading is greater than 50.(00). 1 MMO Decisions IV Has two uncorrected accurate titres within 0.1 cm3. Do not include a reading if it is labelled “rough”. Do not award this mark if, having performed two titres within 0.1 cm3, a further titration is performed which is more than 0.10 cm3 from the closer of the initial two titres, unless a further titration, within 0.1 cm3 of any other, has also been carried out. Do not award the mark if any ‘accurate’ burette readings (apart from initial 0) are given to zero dp. 1

Page 3 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 34 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total 1 (a) (cont) For assessment of accuracy (Q) marks, an Examiner rounds any burette readings to the nearest 0.05 cm3, checks subtractions and then selects the “best” titres using the hierarchy: • two (or more) accurate identical titres (ignoring any that are labelled “rough”), then • two (or more) accurate titres within 0.05 cm3, then • two (or more) accurate titres within 0.10 cm3, etc. These best titres are used to calculate the mean titre, to nearest 0.01 cm3. MMO Quality Award V, VI and VII for δ Y 0.20 cm3 Award V and VI for 0.20 < δ Y 0.30 cm3 Award V for 0.30 < δ Y 0.50 cm3 Spread penalty: if the two ‘best’ titres used by the Examiner are [ 0.50 cm3 apart, cancel one Q mark. If Supervisor titre Y 15 cm3 then tolerances are 0.10, 0.20 and 0.30 cm3. 3 [7] 1 (b) MMO Decisions Check mean titre is correctly calculated from clearly selected values (ticks or working). • Candidate must average two (or more) titres where the total spread is Y 0.20 cm3. • Working must be shown or ticks must be put next to the two (or more) accurate readings selected. • The mean should normally be quoted to 2 dp rounded to the nearest 0.01. [e.g. 26.667 must be rounded to 26.67] Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for 0.025 or 0.075 eg 26.325; allow mean to 1 dp if all accurate burette readings were given to 1 dp (ignoring initial given as 0) and the mean is exactly correct. [e.g. 26.0 and 26.2 = 26.1 is correct but 26.0 and 26.1 = 26.1 is incorrect.] Do not award this mark if: • the rough titre was used to calculate the mean; • candidate carried out only 1 accurate titration; • burette readings were incorrectly subtracted to obtain any of the accurate titre values; • all burette readings (resulting in titre values used in calculation of mean) are integers. 1 [1]

Page 4 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 34 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total 1 (c) (i) (ii) ACE Interpretation I Correctly calculates answer to 1000 0.125 × (b) in (i) and 0.002906 1000 0.125 23.25 = × (0.00291) in (ii) 1 [6] (iii) II Correctly calculates answer to (iii) (ignore sf). If (i) < (ii) then answer must be negative. 1 (iv) (v) PDO Display III Shows use of (iii) × 106 in (iv) and × 2 in (v). (This should be (iii) × 2 but allow (iv) × 2.) 1 (vi) ACE Interpretation IV Correct method [(i) – (v)] × 40 in (vi) 1 (vii) V Correct expression: (vi)] [(iv) (iv) + × 100 in (vii) or correct answer 1 PDO Display VI All quoted answers given to 3 or 4 significant figures except in (iii). (Minimum of 4 answers needed.) 1 [Total 14]

Page 5 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 34 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total 2 (a) PDO Layout I Presents data in list/form in the space provided. Must have all four required weighings and attempt at mass of solid/FB 4 or attempt at mass of carbon dioxide. 1 PDO Recording II Gives all appropriate headings and units • mass/weight of flask + acid • mass of tube + FB 4 • mass of flask + contents (owtte) • mass of tube + residue/mass of tube • mass of FB 4 • mass of CO2/mass lost (minimum of four required pieces of information) Units: /g or (g) or in g or g by each entry (Ignore irrelevant data) 1 II All recorded balance readings consistent to at least 1 decimal place. (minimum of three balance readings) 1 ACE Interpretation IV Correctly calculates the mass of FB 4 added and the mass of carbon dioxide evolved. 1 MMO Quality V and VI Calculate dioxide carbon of mass 4 FB mass to 3 significant figures and compare with Supervisor. Award V and VI for a difference ≤ 0.20 Award V for a difference of 0.20 < δ ≤ 0.50 2 [6]

Page 6 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 34 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total 2 (b) ACE Interpretation (i) Correctly calculates 44 106 from CO mass 2 × (a) to 2 – 4 sf 1 [2] (ii) Correct expression (a) 4 FB (b)(i) from mass 100 × or correct answer to 2–4 sf (Do not penalise sf twice.) 1 2 (c) (i) ACE Interpretation Suggests a suitable significant source of error: • CO2 remains dissolved in acid • Impossible to prevent all acid spray • Reaction does not go to completion/ CO2 not diffused (owtte) from flask • Some FB 4 sticks to the wall of the flask. 1 (ii) ACE Conclusions Would lower %/decrease since less mass lost/CO2 lost/ given out/evolved. Would raise %/increase since more mass lost. Would lower % since less mass lost/CO2 produced. Would lower % since less mass lost/used or less CO2 produced Explanation must follow source of error. If using 1dp balance then allow cannot tell whether the answer should be greater or smaller/% error could be either way 1

Page 7 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 34 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total 2 (c)(iii) ACE Improvement Improvement suggested must be linked to the error (even if imprecisely expressed) identified in (i). Dissolved CO2 Saturate the solution with CO2 before experiment or use warm acid or use less acid. Acid spray Use taller container or cotton wool plug or bung with hole or collect gas in syringe or use less concentrated acid. Going to completion Keep weighing until mass does not go down further or leave for longer or swirl for longer or warm flask and contents or use more concentrated acid. Sticks to side Use beaker or wider-necked flask. If 1dp balance used then allow use balance to 2 or 3 dp. 1 [3] [Total 11]

Page 8 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 34 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total FB 5 is CuCO3(s); FB 6 is Pb(NO3)2(s); FB 7 is ethanedioic (oxalic) acid 3 (a) (i) MMO Collection MMO Decisions Blue solution with FB 5 and colourless solution with FB 6 and (rapid) fizzing/bubbling/effervescence with FB 5. Describes the test on gas from FB 5 with limewater with positive outcome or gas pops with lighted splint in (b)(i). 1 1 expected observations for 3(a)(ii) test FB 5 FB 6 + NaOH (pale) blue ppt insoluble in excess white ppt soluble in excess + NH3 (pale) blue ppt (soluble in excess) forming deep/dark blue solution white ppt insoluble in excess + KI brown (yellow-brown/orange-brown, red-brown) ppt/solid/mixture or off-white ppt with brown solution yellow ppt Question Sections Indicative material Mark Total 3 (a) (ii) MMO Collection FB 5 correct observations with NaOH FB 5 correct observations with NH3 FB 6 correct observations with NaOH and ammonia KI correct observations with FB 5 and FB 6 1 1 1 1 [9] (iii) ACE Conclusions FB 5 contains Cu2+ FB 6 contains Pb2+ (with some evidence) 1 1 (iv) CO3 2– is anion in FB 5 as fizzing / positive limewater test or some valid statement about the anion in FB 6 e.g. could not be carbonate/sulfite as no fizz / could be nitrate as lead nitrate soluble/ not halide/sulfate/sulfite as lead halide/ PbSO4 insoluble or no anion tests carried out so no conclusion possible 1

Page 9 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 34 © Cambridge International Examinations 2013 (b) (i) MMO Collection ACE Conclusions effervescence between solution and Mg ribbon manganate(VII) decolourised FB 7 is an acid and a reducing agent. 1 1 1 [6] (ii) MMO Collection (ii) Any two of • condensation near mouth of tube or steam produced • liquid at bottom of tube/solid melts/solid dissolves/gives colourless solution • charring in the solid/turning black. 1 1 (iii) ACE Conclusions (iii) FB 7 is organic or simple covalent/molecular or FB 7 is hydrated/has water of crystallisation or undergoes thermal decomposition. 1 [Total 15]