Cambridge A Level Chemistry 9701 — 2014 May/June Paper 3 · Variant 4

This document consists of 12 printed pages. [Turn over IB14 06_9701_34/5RP © UCLES 2014 *8715689080* 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 9701/34 Paper 3 Advanced Practical Skills 2 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 9701/34/M/J/14 © UCLES 2014 1 You are to determine the percentage of calcium carbonate in a sample of crushed limestone. You will fi rst react a known mass of the crushed limestone in a known amount of hydrochloric acid, HCl (aq), to make a solution. You may assume that only the calcium carbonate present in the sample will react with the acid. CaCO3(s) + 2HCl (aq) → CaCl 2(aq) + H2O(l) + CO2(g) The amount of acid that did not react with the carbonate is then found by a titration using sodium hydroxide. You may assume that no compounds present in the limestone will react with the sodium hydroxide. NaOH(aq) + HCl (aq) → NaCl (aq) + H2O(l) FB 1 is crushed limestone, impure calcium carbonate. FB 2 is 2.0 mol dm–3 hydrochloric acid, HCl. FB 4 is 0.20 mol dm–3 sodium hydroxide, NaOH. methyl orange indicator (a) Method Read through the method before starting any practical work. Making the solution ● Weigh the container with the limestone, FB 1, and record the mass below. ● Tip all the solid FB 1 into a 250 cm3 beaker. ● Reweigh the container and record the mass. ● Fill the burette with FB 2. ● Slowly run between 47.5 and 48.5 cm3 of FB 2 into the beaker containing FB 1. ● Record, in the space below, both your burette readings and the volume of FB 2 added. ● Stir the mixture carefully until all the solid has reacted. ● Transfer the contents of the beaker into the volumetric flask. ● Rinse the beaker with distilled water and add it to the volumetric flask. Make the solution up to 250 cm3 with distilled water and mix thoroughly. This is solution FB 3.

3 9701/34/M/J/14 © UCLES 2014 [Turn over I II III IV V VI VII VIII IX Titration ● Empty and rinse the burette with distilled water. ● Fill the burette with FB 3 from the volumetric flask. ● Pipette 25.0 cm3 of FB 4 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. ● 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 3 added in each accurate titration. [9] (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 4 required … cm3 of FB 3. [1]

4 9701/34/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) Calculate the number of moles of sodium hydroxide present in 25.0 cm3 of FB 4. moles of NaOH = … mol (ii) Hence state the number of moles of hydrochloric acid present in the volume of FB 3 calculated in (b). moles of HCl = … mol (iii) Use your answer to (ii) to calculate the number of moles of hydrochloric acid present in 250 cm3 of FB 3. moles of HCl in 250 cm3 of FB 3 = … mol (iv) Calculate the number of moles of hydrochloric acid, FB 2, added to FB 1 in (a). moles of HCl added to FB 1 = … mol (v) Use your answers to (iii) and (iv) to calculate the number of moles of hydrochloric acid that reacted with the calcium carbonate in FB 1. moles of HCl reacted with CaCO3 = … mol (vi) Calculate the number of moles of calcium carbonate present in your sample of FB 1. moles of CaCO3 = … mol I II III IV V VI VII

5 9701/34/M/J/14 © UCLES 2014 [Turn over (vii) From your answer to (vi) and the mass of FB 1 used in (a), calculate the percentage by mass of calcium carbonate in the limestone. [Ar: C, 12.0; O, 16.0; Ca, 40.1] percentage of calcium carbonate = … % [7] (d) (i) The maximum error in a single burette reading is ±0.05 cm3. Student X, carrying out this experiment, recorded that 48.50 cm3 of FB 2 was added to FB 1. What are the smallest and largest possible volumes of FB 2 that were added? smallest volume used = … cm3 largest volume used = … cm3 (ii) Student Y used an identical mass of FB 1 but added 47.70 cm3 of FB 2. How would the value obtained in (b) by student X compare with the value obtained by student Y? Explain your answer. … … … [3] [Total: 20]

6 9701/34/M/J/14 © UCLES 2014 2 You are to determine the percentage by mass of calcium carbonate in another sample of the limestone by thermal decomposition. You may assume that none of the other compounds in the limestone sample is affected by heating. The equation for the reaction that occurs is given below. CaCO3(s) → CaO(s) + CO2(g) FB 5 is crushed limestone, impure calcium carbonate. (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 FB 5 into the crucible. ● Weigh the crucible with FB 5 and record the mass. ● Place the crucible on the pipe-clay triangle. ● Heat the crucible gently for about one minute and then strongly for three 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. ● Reheat the crucible strongly for three minutes, cool and reweigh. Record the mass. ● Record the mass of FB 5 used and the mass of solid remaining after the second heating. [2]

7 9701/34/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 total mass of carbon dioxide lost on heating FB 5. mass of CO2 lost = … g (ii) Use your answer to (i) to calculate the mass of calcium carbonate present in the sample of FB 5 heated. [Ar: C, 12.0; O, 16.0; Ca, 40.1] mass of CaCO3 = … g (iii) Calculate the percentage by mass of calcium carbonate in the limestone. percentage of calcium carbonate = … % [3] (c) FB 5 and FB 1 are samples of the same limestone. You have determined the percentage of calcium carbonate in both Questions 1 and 2 using two different procedures. (i) Which procedure is the less accurate? Explain your answer. … … (ii) Suggest a change to the less accurate practical procedure that would improve the accuracy and explain your answer. … … … [2] [Total: 7]

8 9701/34/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. (a) A different sample of limestone was reacted with dilute nitric acid to give solution FB 6. This sample of limestone contained calcium carbonate, CaCO3, 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 identities of the additional ions. test observations (i) To a 1 cm depth of FB 6 in a test-tube add aqueous ammonia. (ii) To a 1 cm depth of FB 6 in a test-tube add a 1 cm depth of aqueous silver nitrate. (iii) To a 1 cm depth of FB 6 in a test-tube add a 1 cm depth of aqueous barium chloride or barium nitrate.

9 9701/34/M/J/14 © UCLES 2014 [Turn over (iv) Suggest all possible identities for the ions present in FB 6, apart from Ca2+ and NO3 –. … (v) Select a reagent to use in a further test on FB 6 to confi rm that one of the cations you have listed in (iv) is not present in FB 6. Carry out your test and complete the table. test observations conclusion To a 1 cm depth of FB 6 in a test-tube add … [6] (b) You are provided with a solid, FB 7. By carrying out the following tests you will be able to identify three of the ions present in FB 7. test observations (i) Place a spatula measure of FB 7 in a hard-glass test-tube. Heat gently at fi rst, then heat more strongly until no further change is seen, then allow the tube to cool. I II III IV V VI

10 9701/34/M/J/14 © UCLES 2014 test observations (ii) Place a spatula measure of FB 7 in a test-tube. Add about a 5 cm depth of dilute nitric acid. You will use the solution formed for tests (iii) to (v). (iii) To a 1 cm depth of the solution in a test-tube add a few drops of aqueous potassium manganate(VII), then add a few drops of starch solution. (iv) To a 1 cm depth of the solution in a test-tube add a few drops of aqueous silver nitrate. (v) To a 1 cm depth of the solution in a test-tube add aqueous ammonia. Use the Qualitative Analysis Notes on pages 11 and 12 to identify three of the ions present. … [7] [Total: 13] I II III IV V VI VII

11 9701/34/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. 9701/34/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 9701/34 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 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 34 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total 1 (a) PDO Layout I Unambiguous headings for 2 balance readings and volume of FB 2 added between 47.5 and 48.5 cm3 1 MMO Collection 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 all accurate data. and volume FB 3 added recorded for each accurate titre. Headings should match readings. • initial/start (burette) reading/volume • final/end (burette) reading/volume • titre or volume/FB 3 used/added (not “difference”) unit: /cm3 or (cm3) or in cm3 or cm3 for each entry 1 MMO Decisions 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) • any burette reading is greater than 50.(00). 1 V Has two uncorrected, accurate titres within 0.1 cm3 Do not include a reading labelled ‘rough’. Do not award this mark if, having performed two titres within 0.1 cm3, a further titration is performed that is more than 0.1 cm3 from the closer of the two initial titres unless further titrations 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 Round any burette readings to the nearest 0.05 cm3. Check and correct subtractions in the titre table. 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 calculated as: Scaled titre = )} mass/100.1 1.6 /500) {(V Supervisor )} mass/100.1 1.6 /500) {(V Cand titre Cand added added × − × − × Examiner compares candidate scaled titre with Supervisor’s titre. (a) MMO Quality Award VI, VII, VIII and IX for δ ≤ 0.40 cm3 Award VI, VII and VIII for 0.40 cm3 < δ ≤ 0.80 cm3 Award VI and VII for 0.80 cm3 < δ ≤ 1.20 cm3 Award VI only for 1.20 cm3 < δ ≤ 2.00 cm3 If the “best” titres are ≥ 0.50 cm3 apart cancel one of the Q marks. 4 [9]

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 34 © 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) (i)&(ii) ACE Interpretation I Correctly calculates 1000 25 0.200× = 5 × 10–3 in (i) and gives 5 × 10–3 in (ii) 1 (iii) II Uses (ii) × (b) 250 in (iii) 1 (iv) III Correct expression 1000 diluted V 2.00 × in (iv) 1 IV Correct expressions (iv) – (iii) in (v) and (v) ÷ 2 in (vi) 1 V (vi) × 100.1 (allow × 100) in (vii) 1 (v)&(vi) VI (answer ÷ correct mass FB 1) × 100 in (vii) 1 (vii) (2 marks) PDO Display VII Answers to steps (iii) to (vii) given to 3 or 4 sf minimum number of steps attempted = 4 to access this mark 1 [7] (d) (i) ACE Interpretation smallest = 48.40, largest = 48.60 1 (ii) Conclusion Correct link between volume of FB 2 used/in excess/ concentration of remaining FB 2 and titre or between concentration/volume FB 3/HCl remaining/in excess and titre. (higher volume/concentration gives smaller titre ora) Correct reference to student(s) X and/or Y 1 1 [3] Qn 1 Total [20]

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 34 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total 2 (a) PDO Recording Headings with units for all four balance readings are tabulated clearly. • mass of crucible • mass of crucible + FB 5 • mass of crucible + contents/residue/solid/FB5 after heating/cooling • mass of crucible + contents/residue/solid/FB5 after re-heating/re-cooling/2nd heating/2nd cooling 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 Records all balance readings to a consistent number of dp (minimum 1 dp and minimum 3 balance readings ) and records mass of FB 5 (at start) and mass of solid remaining owtte Headings for the two masses of solid must be unambiguous. 1 [2] (b) (i) ACE Interpretation Correct mass loss from results in (a) 1 (ii) PDO Display Shows correct use of 100.1 and 44: 44 100.1 × (i) 1 (iii) ACE Interpretation calculates 100 mass ans × 5 FB (ii) 1 [3] (c) (i) ACE Conclusion Thermal decomposition is less accurate because not all carbonate has decomposed. Temperature used not high enough to decompose solid Percentage of CaCO3 is much less in Question 2 1 (ii) Improvement Heat to constant mass. Use a gas/Bunsen burner/furnace If candidates achieve constant mass and give titration less accurate as more steps then award 1 mark. 1 [2] Qn 2 Total [7]

Page 5 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 34 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total FB 6 is MgSO4 + HNO3(aq); FB 7 is ZnCO3(s) + KI(s) 3 (a) MMO Collection I White ppt with NH3 insoluble in excess 1 II No visible reaction/no change and White ppt 1 ACE Conclusion III Mg2+ and Al 3+ and SO4 2– and/or SO3 2– in (iv) 1 MMO Decisions IV Selects NaOH in (v). (Allow KI/ HCl/ H2SO4/K2CrO4 if Pb2+ in (iv)) 1 Collection V White ppt insoluble in excess (NaOH) (Allow no reaction with KI if Pb2+ in (iv)) 1 ACE Conclusion VI (not) Al 3+ / Mg2+ is present Allow ecf from incorrect cations in (iv) and correct observation with NaOH 1 [6] (b) (i) MMO Collection I Solid turns yellow on heating and paler yellow/white on cooling 1 (ii) II Effervescence and gas turns limewater milky (or in (i)) 1 (iii) III (Solution turns) (darker) yellow/orange/red/brown and blue/black with starch 1 (iv) IV (Pale) yellow ppt 1 (v) ACE Conclusion V White ppt soluble in excess 1 VI and VII Identifies all three ions (Zn2+, CO3 2– and I–) VI only Identifies two ions. Minimum evidence: Zn2+ white ppt soluble in excess NH3 CO3 2– effervescence or positive limewater I– either (iii) or (iv) correct 1 1 [7] Qn 3 Total [13]