Cambridge A Level Chemistry 9701 — 2013 Oct/Nov Paper 3 · Variant 6

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 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 9701/36 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 12 printed pages. [Turn over IB13 11_9701_36/4RP © UCLES 2013 *7736236717* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/36/O/N/13 © UCLES 2013 For Examiner’s Use 1 In this experiment you are to determine the concentration of aqueous potassium manganate(VII), FB 3, by titration. In the titration potassium manganate(VII) is fi rst reacted with acidifi ed potassium iodide to produce iodine. The amount of iodine formed is then determined by titrating the mixture with sodium thiosulfate. FB 1 is hydrated sodium thiosulfate, Na2S2O3.5H2O. FB 2 is dilute sulfuric acid, H2SO4. FB 3 is aqueous potassium manganate(VII), KMnO4. FB 4 is aqueous potassium iodide, KI. starch indicator (a) Method Preparing a solution of FB 1 ● Weigh the 250 cm3 beaker and record the mass in the space below. ● Add all the FB 1 to the beaker. Weigh the beaker with FB 1 and record the mass. ● Calculate the mass of FB 1 used and record this in the space below. ● Add approximately 100 cm3 of distilled water to the beaker. Stir until all the solid has dissolved. ● Transfer the solution into the 250 cm3 volumetric (graduated) flask labelled FB 5. ● Wash out the beaker thoroughly using distilled water and add the washings to the volumetric flask. Make the solution up to the mark using distilled water. ● Shake the flask thoroughly to mix the solution before using it for your titrations. ● This solution of sodium thiosulfate is FB 5. Titration ● Use the measuring cylinder to add 20 cm3 of FB 2 to a conical flask. ● Use the measuring cylinder to add 10 cm3 of FB 4 to the same flask. ● Pipette 25.0 cm3 of FB 3 into the same flask. The colour of the mixture is caused by iodine. ● Fill the burette with FB 5. ● Begin each titration without adding the starch indicator. Add 10 drops of starch indicator when the colour of the mixture becomes (pale) yellow. The end-point is when the blue-black colour caused by the starch disappears. ● Perform a rough titration and record your burette readings in the space below. The rough titre is … cm3.

3 9701/36/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use I II III IV V VI VII ● Carry out as many accurate titrations as you think necessary to obtain consistent results. ● Make sure 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 5 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. suitable value = … cm3 of FB 5 [1] (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 thiosulfate, FB 1, that were weighed out. The relative formula mass of hydrated sodium thiosulfate is 248.2. moles of sodium thiosulfate = … mol (ii) Calculate the number of moles of sodium thiosulfate that were present in the volume of FB 5 calculated in (b). moles of sodium thiosulfate = … mol

4 9701/36/O/N/13 © UCLES 2013 For Examiner’s Use I II III IV V (iii) Iodine produced by the reaction in the conical fl ask reacts with sodium thiosulfate. Use the equation below to calculate the number of moles of iodine that reacted with sodium thiosulfate in (ii). I2 + 2Na2S2O3 → 2NaI + Na2S4O6 moles of I2 = … mol (iv) The iodine is produced as a result of the oxidation of iodide ions in potassium iodide, FB 4, by potassium manganate(VII), FB 3. The ionic equation for this reaction is 2MnO4 – + 16H+ + 10I– → 2Mn2+ + 5I2 + 8H2O Calculate the number of moles of potassium manganate(VII), KMnO4, that reacted to produce the iodine in (iii). moles of KMnO4 = … mol (v) Calculate the concentration of potassium manganate(VII), in g dm–3, in FB 3. (Ar : O, 16.0 ; K, 39.1; Mn, 54.9) concentration of KMnO4 = … g dm–3 [5] (d) (i) State the maximum error in any single reading of the burette. maximum error = … cm3 (ii) Calculate the maximum percentage error in volume of FB 5 in your fi rst accurate titre. maximum percentage error = … % [1] [Total: 14]

5 9701/36/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use I II III IV V VI 2 In this experiment you will heat two separate samples of a hydrated salt to drive off the water of crystallisation. You will then calculate the relative atomic mass of the metal in the salt. FB 6 is the hydrated salt. The formula of FB 6 is MSO4.7H2O, where M is the metal. (a) Method Record all weighings, in an appropriate form, in the space below. ● Record the mass of the empty crucible without its lid. ● Add between 2.0 and 2.4 g of FB 6 into the crucible. Record the mass of the crucible and its contents. ● Use a pipe-clay triangle to support the crucible and contents on a tripod. ● Heat the crucible and its contents gently and carefully for about two minutes, with the lid off. Then heat very strongly for a further three minutes. ● Put the lid on the crucible and leave it to cool for approximately 10 minutes. While you are waiting for the crucible to cool, start work on Question 3. ● When the crucible is cool, remove the lid, and weigh the crucible with the residue. ● Record the mass of anhydrous MSO4 remaining in the crucible after heating and therefore calculate the mass of water lost. ● To prepare for the second experiment, use a spatula to remove the solid residue from the crucible into the beaker labelled waste. ● Reweigh the empty crucible without its lid. ● Carry out the experiment again. This time use between 2.5 and 2.9 g of FB 6. [6]

6 9701/36/O/N/13 © UCLES 2013 For Examiner’s Use (b) Calculation Show your working and give your answers to three signifi cant fi gures. (i) State and explain which of your two experiments in (a) is likely to be the more accurate. … … … (ii) Calculate the number of moles of water removed from the hydrated salt in the more accurate experiment. (Ar : H, 1.0; O, 16.0) moles of H2O = … mol (iii) Complete the equation for the removal of water from hydrated FB 6. Include state symbols. MSO4.7H2O (…) → …(…) + …(…) (iv) Using your answer to (ii), calculate the number of moles of anhydrous MSO4 produced in the more accurate experiment. moles of MSO4 = … mol (v) Use the mass of anhydrous MSO4 produced in the more accurate experiment to calculate the relative formula mass of MSO4. relative formula mass of MSO4 = …

7 9701/36/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (vi) Calculate the relative atomic mass of M. (Ar : O, 16.0; S, 32.1) (If you were unable to calculate the relative formula mass of anhydrous MSO4 you may assume that it was 126.3. This is not the correct value.) Ar of M = … (vii) The relative atomic masses of some of the cations on page 11 are given below. (Ar : Mg, 24.3; Ca, 40.0; Fe, 55.8; Cu, 63.5; Mn, 54.9; Zn, 65.4) M is a cation of one of the elements listed above. Suggest the identity of M and justify your answer. … … (viii) Suggest why it was not necessary to include the cations aluminium and chromium from page 11 in the list of relative atomic masses in (vii). … … … [8] (c) The crucible was cooled with the lid on to prevent absorption of water vapour from the air. Suggest a better way of preventing water vapour being absorbed during cooling. … … [1] [Total: 15]

8 9701/36/O/N/13 © UCLES 2013 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. 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 will carry out further tests on the ions in FB 6. ● Put a spatula measure of FB 6 into a test-tube. ● Half fill the test-tube with distilled water and stir until the solid dissolves. ● Use a 1 cm depth of the solution of FB 6 in separate test-tubes for the tests you will carry out. (i) Add aqueous sodium hydroxide to FB 6 solution. Add aqueous ammonia to FB 6 solution. Record your observations below. (ii) Carry out a test of your choice to show that sulfate ions are present in FB 6. reagent(s) used … observation(s) … … (iii) Give the ionic equation for the reaction in test (ii). … [4]

9 9701/36/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (b) FB 7, FB 8 and FB 9 are aqueous solutions, each containing one cation and one anion. None of the cations and none of the anions in FB 7, FB 8 and FB 9 are identical. (i) Add a 2 cm magnesium strip to a 2 cm depth of each solution in a clean test-tube. Mix pairs of solutions as shown so that you can complete the table shown below. Use 1 cm depths of solutions in clean test-tubes. Record your observations in the table. FB 7 FB 8 FB 9 add a 2 cm strip of magnesium ribbon FB 7 [Keep this mixture for use in test (iii)] FB 8 (ii) The anion present in FB 7 is the sulfate ion. Identify FB 7, giving evidence from your observations. FB 7 is … . evidence … …

10 9701/36/O/N/13 © UCLES 2013 For Examiner’s Use (iii) Add a 1 cm depth of aqueous hydrogen peroxide, FB 10, to the mixture of FB 7 and FB 9 that you kept from (i). Then add three drops of starch. Record your observation(s). Identify the coloured chemical produced when hydrogen peroxide was added to the mixture of FB 7 and FB 9 and name the anion present in FB 9. observations … … chemical produced … anion in FB 9 … (iv) Give the chemical formula of the substance you observed when solutions FB 8 and FB 9 were mixed. … [7] [Total: 11]

11 9701/36/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.]

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. 9701/36/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

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2013 series 9701 CHEMISTRY 9701/36 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 36 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total 1 (a) PDO layout I The following data are given • mass of solid used (or both weighings) • volume used in rough titre (or both readings) • initial and final readings for two (or more) accurate titrations 1 PDO recording II Acceptable/appropriate headings for all data given in weighing and accurate titration tables and g and cm3 units. • mass/weight of beaker (empty) • mass of beaker + FB 1/solid • mass solid/FB1 • initial/start/first (burette) reading/volume • final/end/second (burette) reading/volume • titre or volume used/added/FB 5 added (but not difference or change in volume) • unit:/cm3 or (cm3) or in cm3 or cm3 If g/cm3 units are not given in the heading, every entry in the table must have the correct unit. 1 PDO recording III All accurate burette readings are to the nearest 0.05 cm3. The need to record to 0.05 only applies to the burette readings, including 0.00 cm3 (if this was the initial reading), but it does not apply to the titre. 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 decision IV There are two uncorrected accurate titres within 0.10 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 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 zero) are given as integers. 1 MMO quality Examiner calculates mean titre × mass FB 1 for candidate and Supervisor. Award V, VI and VII if δ ≤ 2 (g cm3) Award V and VI if 2 < δ ≤ 3 Award V, only, if 3 < δ ≤ 5. Spread penalty: if two best titres used by the Examiner are ≥ 0.50 cm3 apart, cancel one Q mark. 1 1 1 [7]

Page 3 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 36 © Cambridge International Examinations 2013 1 (b) MMO decision Candidate calculates the mean correctly. Candidate must take the average two (or more) titres where the total spread is ≤ 0.2 cm3. Working must be shown or ticks must be put next to the accurate titres selected. The mean should normally be quoted to 2 dp, rounded to nearest 0.01 cm3. Example 26.667 cm3 must be rounded to 26.67 not 26.65 cm3, 26.675 cm3 must be rounded to 26.68 not 26.70 cm3. Two special cases, where the mean may not be to 2 dp: Allow mean expressed to 3 dp, only for 0.025 or 0.075. Allow mean if expressed 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 wrong – should be 26.05. Do not award this mark if: • The rough titre was used to calculate the mean. • The candidate did only one 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. Note: the candidate’s mean will sometimes be marked correct even if it is different from the mean calculated by the Examiner for the purpose of assessing accuracy. 1 [1] 1 (c) ACE interpretation I Correctly calculates moles of Na2S2O3 weighed in (i) = mass of FB1 used 248.2 1 II Correct expression for moles of Na2S2O3 used in (ii) = answer (i) × mean titre 250 1 III Correct calculations/expression in (iii) and (iv) (iii) : no moles of I2 = 0.5 × (ii) 1 PDO display IV Correct expression in (v) Mass = answer (iv) × 40 ×158(.0) (× 40 may be shown as × 1000/25) 1 PDO display V All quoted answers are given to 3 or 4 significant figures. (minimum of three answers) 1 [5]

Page 4 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 36 © Cambridge International Examinations 2013 1 (d) ACE interpretation error = 0.05 cm3 in (i) and % error in volume of FB 5 = used of vol 0.05 2 5 FB × × 100 in (ii) 1 [1] [Total: 14] 2 (a) MMO collection I The masses of FB 6 used by the candidate were between 2.0 – 2.4 g (expt 1) and 2.5 – 2.9 g (expt 2). 1 PDO display II Suitable headings for a table or list, shown completely for at least one experiment. If 2 experiments, all headings must be correct. • (mass of) empty crucible • (mass of) crucible + FB 6 • (mass of) crucible + residue/FB 6 after heating • mass (water) lost or mass anhydrous remaining and unit covering every weighing. Unit/g or (g) or in grams or g following each weighing. 1 PDO recording III Records all balance readings consistently to at least 1 dp A minimum of three weighings are needed. 1 MMO quality Examiner calculates water of mass salt hydrated of mass for each experiment. Award IV if the ratio in expt 1 is between 0.95 and 1.15. Award V If the ratio in expt 2 is between 0.95 and 1.15. Award VI If the ratio in both of experiments 1 and 2 is between 0.85 and 1.25. 1 1 1 [6] 2 (b) MMO quality (i) An appropriate choice of the more accurate experiment, and justification of choice. Three possibilities: • Experiment 2 uses a larger mass and has a greater percentage accuracy. • A reference to either experiment “spitting” or “frothing” during heating is a valid reason for nominating the other experiment. • Experiment 1 as smaller mass takes less heating. 1 ACE interpretation (ii) Correctly calculates number of moles of water = mass of water lost 18 Ans to 2–4 sf Candidate must use the mass loss for the experiment thought to be more accurate. (If no choice is expressed in (i), this should be expt 2.) 1 ACE conclusion (iii) MSO4.7H2O(s)
MSO4(s) + 7H2O(g) Allow (l) for water. 1

Page 5 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 36 © Cambridge International Examinations 2013 ACE interpretation (iv) Correct answer calculated n(MSO4) = n(water) 7 i.e. answer (ii) divided by 7 Ans to 2–4 sf 1 ACE interpretation (v) Method mark showing the numbers for the expression Relative formula mass = mass of residue no of moles Mass of residue from same expt as mass of water Ans to 2–4 sf 1 ACE interpretation (vi) Correct answer calculated Ar = Mr – 96.1 . Candidates are allowed to use 126.3 as the Mr. In this case, the Ar = 30.2. Ans 2–4 sf Penalise sf once only within (b) 1 ACE conclusion (vii) Correct identification of M as magnesium and explanation that this Ar is closest to value calculated. Allow alternative identity of metal as ecf from Ar value. 1 ACE conclusion (viii) (M is divalent but) Al and Cr are both trivalent or (M forms 2+ ion whereas) Al and Cr are 3+ or sulfates of Cr/Al are not CrSO4 and AlSO4 (ora) ref to both needed 1 [8] 2 (c) ACE Improvement s Cool in a desiccator or cool in closed container with a (named) drying agent 1 [1] [Total: 15]

Page 6 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 36 © Cambridge International Examinations 2013 FB 6 = MgSO4; FB 7 is H2SO4; FB 8 is Pb(NO3)2; FB 9 = KI 3 (a) MMO collection (i) White precipitate, insoluble in excess for both NaOH and NH3 1 MMO decision (ii) Use barium chloride/nitrate and hydrochloric/nitric acid 1 MMO collection White precipitate formed, insoluble in acid. 1 ACE conclusion (iii) Ba2+ + SO4 2-
BaSO4 1 [4] 3 (b) MMO collection (i) One mark for each column 1 FB 7 FB 8 FB 9 Mg Fizzing or tube gets hot/heat given out or Mg dissolves and (gas) pops with lighted splint Black solid/ppt formed/Mg strip turns dark No reaction FB 7 White ppt No reaction FB 8 Yellow ppt 1 1 ACE conclusion (ii) FB 7 is sulfuric acid and it is acidic (or H+ ions are present) because it fizzes/hydrogen produced with magnesium. 1 MMO collection (iii) Red-brown/brown/orange-brown/yellow-brown colour with KI (not red or orange or yellow) and blue or black colour with starch 1 ACE conclusion Iodine produced and the anion in FB 9 is iodide. 1 ACE conclusion (iv) PbI2 or AgI (or both) Ecf possible for CrO4 2- in (iii) with Ba2+ or Pb2+ 1 [7] [Total: 11]