Cambridge A Level Chemistry 9701 — 2014 May/June Paper 3 · Variant 5

This document consists of 12 printed pages. [Turn over IB14 06_9701_35/4RP © UCLES 2014  Session Laboratory For Examiner’s Use 1 2 3 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 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. CHEMISTRY 9701/35 Paper 3 Advanced Practical Skills 1 May/June 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

2 9701/35/M/J/14 © UCLES 2014 1 Limewater is a saturated solution of calcium hydroxide. A sample of limewater was diluted to produce solution FA 1. You are to determine the concentration of calcium hydroxide, Ca(OH)2, in FA 1 by titration with hydrochloric acid, HCl, which you will fi rst dilute. The equation for the reaction between calcium hydroxide and hydrochloric acid is given below. Ca(OH)2(aq) + 2HCl (aq)  CaCl 2(aq) + 2H2O(l) FA 1 is aqueous calcium hydroxide, Ca(OH)2. FA 2 is 0.500 mol dm–3 hydrochloric acid, HCl. methyl orange indicator (a) Method Read through the method before starting any practical work. (i) Dilution ● Fill the burette with FA 2. ● Run between 24.00 and 26.00 cm3 of FA 2 into the 250 cm3 volumetric flask. ● Record your burette readings and the volume used in the space below. ● Make up the solution to 250 cm3 with distilled water and shake the flask to ensure thorough mixing. This solution is FA 3. volume of 0.500 mol dm–3 HCl used = … cm3 (ii) Titration ● Empty and rinse the burette. ● Fill the burette with FA 3. ● Pipette 25.0 cm3 of FA 1 into a conical flask. ● Add a few drops of methyl orange indicator. ● Perform a rough titration and record your burette readings in the space below. The rough titre is … cm3.

3 9701/35/M/J/14 © UCLES 2014 [Turn over I II III IV V VI VII VIII ● 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 FA 3 added in each accurate titration. [8] (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 FA 1 required … cm3 of FA 3. [1]

4 9701/35/M/J/14 © UCLES 2014 (c) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Use your volume of FA 2 from (a)(i) to calculate the concentration of FA 3. concentration of FA 3 = … mol dm–3 (ii) Use your answer to (c)(i) and the value calculated in (b) to calculate the number of moles of hydrochloric acid used to neutralise 25.0 cm3 of FA 1. moles of HCl = … mol (iii) Use your answer to (c)(ii) to calculate the number of moles of calcium hydroxide in 25.0 cm3 of FA 1. moles of Ca(OH)2 = … mol (iv) Use your answer to (c)(iii) to calculate the concentration, in mol dm–3, of calcium hydroxide in FA 1. concentration of Ca(OH)2 = … mol dm–3 [5] I II III IV V

5 9701/35/M/J/14 © UCLES 2014 [Turn over (d) (i) The maximum error in a single burette reading is 0.05 cm3. When making up the diluted acid, FA 3, a student recorded that 24.80 cm3 of FA 2 was used. What are the smallest and largest possible volumes of acid that were run into the volumetric fl ask? smallest volume used = … cm3 largest volume used = … cm3 (ii) If the actual volume of acid added had been less than 24.80 cm3, how would the value the student calculated for the concentration of Ca(OH)2 in (c)(iv) compare to the true value? Explain your answer. … … … [2] (e) If a sample of limewater is left open to the air, the concentration of calcium hydroxide decreases. Explain why. … … [1] [Total: 17]

6 9701/35/M/J/14 © UCLES 2014 2 You are to determine the percentage by mass of zinc carbonate in a sample of powdered zinc carbonate ore by means of thermal decomposition. You may assume that none of the other components of the ore is affected by heating. The equation for the reaction occurring is given below. ZnCO3(s)  ZnO(s) + CO2(g) FA 4 is zinc carbonate ore. (a) Method Read through the method before starting any practical work and prepare a table for your results in the space below. ● Weigh the empty crucible and record the mass in your table. ● Transfer all the FA 4 into the crucible. ● Weigh the crucible with FA 4 and record the mass. ● Place the crucible on the pipe-clay triangle. ● Heat the crucible gently for about one minute and then strongly for four minutes. ● Remove the Bunsen burner and allow the crucible to cool. ● While the crucible is cooling start working on another question. ● Reweigh the cooled crucible with contents and record the mass. ● Record the mass of FA 4 used and the mass of solid remaining after heating. ● Beneath your table, record any observations you have made while the solid was heated and cooled. [4] I II III IV

7 9701/35/M/J/14 © UCLES 2014 [Turn over (b) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) From your results in (a), calculate the mass of carbon dioxide lost on heating FA 4. mass of CO2 lost = … g (ii) Use your answer to (i) to calculate the mass of zinc carbonate present in the sample of FA 4 that was heated. [Ar: C, 12.0; O, 16.0; Zn, 65.4] mass of ZnCO3 = … g (iii) Calculate the percentage by mass of zinc carbonate in the zinc carbonate ore. percentage of ZnCO3 = … % [4] (c) Suggest how a student, using all the same apparatus, could alter the method to be more confi dent that the percentage of zinc carbonate is correct. Explain your answer. … … … … [2] [Total: 10] I II III IV

8 9701/35/M/J/14 © UCLES 2014 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.

9 9701/35/M/J/14 © UCLES 2014 [Turn over (a) You are provided with a different sample of zinc carbonate ore, labelled FA 5. This sample contains zinc carbonate, ZnCO3, and one other salt. This additional salt contains a single cation and a single anion from those listed on pages 11 and 12. By carrying out the following tests you will be able to suggest the identities of the ions in the additional salt. test observations (i) Transfer the solid FA 5 into a boiling tube and add a 3 cm depth of dilute nitric acid to make solution FA 6. Use this solution in tests (ii) to (v). (ii) To a 1 cm depth of FA 6 in a test-tube, add aqueous sodium hydroxide. (iii) To a 1 cm depth of FA 6 in a test-tube, add aqueous ammonia. (iv) To a 1 cm depth of FA 6 in a test-tube, add a 1 cm depth of aqueous silver nitrate. (v) To a 1 cm depth of FA 6 in a test-tube, add a 1 cm depth of aqueous barium chloride or barium nitrate. (vi) Suggest the identity of the cation and anion (apart from Zn2+ and CO3 2–) present in FA 5. Explain your choice. cation … reason … anion … reason … [7] I II III IV V VI VII

10 9701/35/M/J/14 © UCLES 2014 (b) You are provided with solid FA 7, which is a mixture of two salts. Use separate portions of FA 7 to perform the experiments below. test observations (i) Heat a spatula measure of FA 7 in a hard-glass test-tube gently at fi rst, then heat more strongly and test the gas evolved with litmus paper. Dissolve a spatula measure of FA 7 in a test-tube with a 5 cm depth of distilled water for use in tests (ii) and (iii). (ii) To a 1 cm depth of FA 7(aq) in a test-tube, add aqueous silver nitrate, followed by aqueous ammonia. (iii) To a 1 cm depth of FA 7(aq) add barium chloride or barium nitrate, followed by dilute nitric acid. (iv) Use your observations and the Qualitative Analysis Notes from pages 11 and 12 to identify three of the ions present. Give evidence for your choice of ions. ion … evidence … … ion … evidence … … ion … evidence … … [6] [Total: 13] I II III IV V VI

11 9701/35/M/J/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

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. 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. 9701/35/M/J/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

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2014 series 9701 CHEMISTRY 9701/35 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 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 2014 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 2014 9701 35 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total 1 (a) MMO Collection I Burette readings and correct volume given for dilution and volume between 24.00 and 26.00 cm3 1 PDO Layout II 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 Recording III Appropriate headings and units for accurate titration. and volume FA 3 added recorded for each accurate titre. Headings should match readings. • initial/start (burette) reading/volume • final/end (burette) reading/volume • titre or volume/FA 1 used/added (but not “difference”) unit: /cm3 or (cm3) or in cm3 or cm3 for each entry 1 IV 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) 1 MMO Decisions V Has two uncorrected, accurate titres within 0.1 cm3 Do not consider the rough even if ticked. 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 titration 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 Round any burette readings to the nearest 0.05 cm3. Check and correct subtractions in the dilution and titre tables. Examiner then selects the “best” titre using the hierarchy: two identical; titres within 0.05 cm3; titres within 0.1 cm3; etc. Candidate scaled titre = Cand vol diluted × Cand mean titre/Sup vol diluted Examiner compares candidate scaled titre with Supervisor’s titre. (a) MMO Quality VI, VII and VIII Award VI, VII and VIII for δ ≤ 0.20 cm3 Award VI and VII for 0.20 cm3 < δ ≤ 0.40 cm3 Award VI only for a difference of 0.40 < δ ≤ 0.60 cm3 If the “best” titres are ≥ 0.50 cm3 apart cancel one of the Q marks. 3 [8]

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 35 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total (b) ACE Interpretation Candidate must average two (or more) titres that are all within 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. Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for 0.025 or 0.075 e.g. 26.325; allow mean to 1 dp if all accurate burette readings were given to 1 dp 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. Note: the candidate’s mean will sometimes be marked as correct even if it is different from the mean calculated by the Examiner for the purpose of assessing accuracy. 1 [1] (c) ACE Interpretation I Correctly evaluates 250 diluted vol 0.500 × in (i) 1 II Correctly calculates (i) × 1000 (b) in (ii) 1 III Correctly calculates (ii) ÷ 2 in (iii) 1 IV Correctly calculates (iii) × 25 1000 in (iv) 1 PDO Display V All answers given to 3 or 4 sf minimum 3 steps attempted to access this mark 1 [5] (d) ACE Interpretation Conclusion (i) smallest = 24.70, largest = 24.90 (ii) lower conc FA 3 leads to greater titre therefore greater conc. of Ca(OH)2 1 1 [2] (e) ACE Conclusion limewater reacts with carbon dioxide in air 1 [1] Qn 1 Total [17]

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 35 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total 2 (a) PDO Layout I Headings with units and three balance readings and two correctly calculated masses of solid are tabulated clearly. Mass /g, (g), in g, in grams If units are omitted from the headings then they must appear next to each entry in the table. 1 MMO Collection II White solid turns yellow/green-yellow on heating and white/becomes paler on cooling 1 On Supervisor script calculate mass FA 4 ÷ mass loss to 1 dp. Calculate FA 4 ÷ mass loss for the candidate to 1 dp and calculate difference from Supervisor. (a) MMO Quality III and IV Award III and IV if δ ≤ 0.5. Award IV only if 0.5 < δ ≤ 1.0. 1 1 [4] (b) ACE Interpretation I Correctly calculates mass loss from results in (a) in (i) 1 II Correctly calculates Mr: ZnCO3 = 125.4 and CO2 = 44(.0) in (ii) 1 PDO Display III Uses 44 125.4 × (i) in (ii) (allow ecf) 1 IV Uses 4 FA (ii) mass correct 100 × in (iii) 1 [4] (c) ACE Improvement Interpretation Heat to constant mass/ use larger mass All decomposes/all CO2 given off smaller % error 1 1 [2] Qn 2 Total [10]

Page 5 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 35 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total FA 5 is ZnCO3(s) + Al 2(SO4)3(s) FA 7 is NH4Cl (s) + NaHCO3(s) 3 (a) (i) MMO Collection I Effervescence (and colourless solution) 1 (ii) II White ppt with NaOH soluble in excess 1 (iii) III White ppt with NH3 insoluble/partially soluble in excess 1 (iv) IV No reaction/no change/no ppt 1 (v) V White ppt (if additional HCl/HNO3 added then ppt must remain) 1 (vi) ACE Conclusion VI Al 3+ 1 VII SO4 2– as white ppt with Ba2+ 1 [7] (b) (i) MMO Collection I Condensation or sublimation (allow misty/white fumes) (on gentle heating) and (gas/NH3) turns (damp) red litmus blue 1 (ii) II White/off-white/cream ppt soluble in NH3 1 (iii) III No reaction or white ppt in 1st box (allow no ppt) and effervescence in 2nd box 1 MMO Decisions IV Uses limewater in either 3rd test or in (a)(i) 1 (iv) ACE Conclusion V and VI Identifies NH4 +, Cl – and CO3 2– or SO3 2– with appropriate evidence. 1 V only Identifies all three ions without evidence or identifies two ions with evidence. ion minimum evidence NH4 + gas turning litmus blue/NH3 (provided correct litmus result in obs) Cl – white ppt with AgNO3 CO3 2– SO3 2– (rapid) effervescence with acid white ppt with Ba2+ and effervescence/ppt dissolves in acid 1 [6] Qn 3 Total [13]