Cambridge A Level Chemistry 9701 — 2014 May/June Paper 3 · Variant 2

This document consists of 11 printed pages and 1 blank page. [Turn over IB14 06_9701_32/5RP © UCLES 2014  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 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 9701/32 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 Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/32/M/J/14 © UCLES 2014 1 Carbon dioxide in the atmosphere dissolves in rain water making it acidic. When this water passes through limestone containing calcium carbonate, it forms solutions of calcium hydrogen carbonate. In this experiment, you will determine the concentration of hydrogen carbonate ions in a solution by titration with hydrochloric acid. FB 1 is 0.100 mol dm–3 hydrochloric acid, HCl. FB 2 contains an unknown concentration of hydrogen carbonate ions, HCO3 –. methyl orange indicator (a) Method ● Fill the burette with FB 1. ● Pipette 25.0 cm3 of FB 2 into a conical flask. ● Add a few drops of methyl orange indicator to the conical flask. ● 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] I II III IV V VI VII

3 9701/32/M/J/14 © UCLES 2014 [Turn over I II (b) From your accurate titration results obtain a suitable value to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FB 2 required … cm3 of FB 1. [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 hydrochloric acid present in the volume of FB 1 calculated in (b). moles of HCl = … mol (ii) Write the ionic equation for the reaction of FB 1 with FB 2. … (iii) Calculate the concentration, in mol dm–3, of hydrogen carbonate ions in FB 2. concentration of HCO3 – in FB 2 = … mol dm–3 [2] [Total: 10]

4 9701/32/M/J/14 © UCLES 2014 I II III IV 2 As well as hydrogen carbonate ions, water that has passed through rocks also contains a range of metal ions such as Ca2+. The presence of Ca2+ ions leads to the water forming scum with certain types of soap. Soluble metal carbonates can be added to remove these ions. One such soluble carbonate is M2CO3.10H2O. In this experiment you will heat a sample of the carbonate salt to remove the water of crystallisation and leave the anhydrous salt, M2CO3. By working out how much water was lost you will be able to calculate the relative formula mass of M2CO3.10H2O and hence identify M. FB 3 is the hydrated salt, M2CO3.10H2O. (a) Method ● Weigh a clean, dry crucible and its lid. ● Transfer all the FB 3 into the crucible and put the crucible lid on. ● Reweigh the crucible, the lid and the contents. ● Place the crucible on the pipe-clay triangle. ● Heat the crucible very gently for 5 minutes. ● Remove the lid and heat strongly for a further 5 minutes. ● Allow the crucible to cool. You should start Question 3 while cooling is taking place. ● When the crucible is cool enough to handle, reweigh the crucible, the lid and the contents. Record, in an appropriate form in the space below, all your weighings and calculations including the mass of FB 3 used and the mass of water lost. [4] (b) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Use the mass of water lost on heating to calculate the number of moles of hydrated salt, M2CO3.10H2O, in the initial sample. [Ar: H, 1.0; O, 16.0] moles of M2CO3.10H2O = … mol

5 9701/32/M/J/14 © UCLES 2014 [Turn over (ii) Calculate the relative formula mass of M2CO3.10H2O, FB 3. relative formula mass of M2CO3.10H2O = … (iii) Identify M in the salt, FB 3. [Ar: H, 1.0; Li, 6.9; C, 12.0; O, 16.0; Na, 23.0; K, 39.1; Rb, 85.5; Cs, 133] M is … . [5] (c) (i) State the maximum error in the mass of FB 3 you recorded in (a). maximum error in the mass of FB 3 = … g (ii) Calculate the maximum percentage error in the mass of water lost in (a). percentage error = …% [1] (d) Suggest a change to the method that would improve the accuracy of this experiment. Explain your answer. … … … … [2] [Total: 12] I II III IV V I II III

6 9701/32/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.

7 9701/32/M/J/14 © UCLES 2014 [Turn over (a) Water in rivers and streams contains a range of different cations and anions. A particular salt occurs in some samples of spring water. You will carry out tests to identify this salt. FB 4 is a solution of the salt. It contains one cation, which is listed in the Qualitative Analysis Notes on page 10. It also contains one anion, which is either sulfate, SO4 2–, or sulfi te, SO3 2–. (i) Choose reagents that will allow you to identify the cation in FB 4. Carry out suitable tests using these reagents and record your observations in the space below. The cation in FB 4 is … . (ii) Choose reagents to identify the anion in FB 4. Carry out suitable tests using these reagents and record your results in the space below. The anion in FB 4 is … . [8] I II III IV V VI VII VIII

8 9701/32/M/J/14 © UCLES 2014 Before starting parts (b) and (c), half-fi ll a 250 cm3 beaker with water and heat with a Bunsen burner to approximately 60 C. You will use this as a hot water bath. Turn off the Bunsen burner. (b) FB 5, FB 6 and FB 7 are solutions each containing a single compound which could be ethanol, ethanal or propanone. To identify each compound you will react the samples with Tollens' reagent and with acidifi ed potassium manganate(VII). (i) Preparation of Tollens' reagent ● To approximately 2 cm depth of aqueous silver nitrate in a boiling tube, add approximately 0.5 cm depth of aqueous sodium hydroxide. ● Add aqueous ammonia a little at a time with continuous shaking until the brown precipitate just dissolves. Do not add an excess of ammonia. test observations FB 5 FB 6 FB 7 To a 1 cm depth of each solution in a clean, dry test-tube add a few drops of the Tollens’ reagent that you have prepared. Do not shake the tube. If no reaction is seen, warm the tube in the hot water bath. When you have made your observations, rinse out all the test-tubes and the boiling tube which were used with Tollens’ reagent. To a 1 cm depth of each solution in a test-tube add a 1 cm depth of dilute sulfuric acid. Then add a few drops of aqueous potassium manganate(VII). If no reaction is seen, warm the tube in the hot water bath. Do not carry out this test (ii) Identify each compound. FB … contains ethanol. FB … contains ethanal. FB … contains propanone. I II III IV V

9 9701/32/M/J/14 © UCLES 2014 [Turn over (iii) Another reagent can be used with these samples to identify which compounds have a carbonyl group, C=O. This reagent has not been supplied so you cannot carry out this test. State the reagent and the expected observations of the three tests. reagent: … expected observations FB 5 … FB 6 … FB 7 … [7] (c) FB 8 is an aqueous solution of an organic compound. Carry out the following tests. You do not need to identify FB 8. test observations To a 1 cm depth of FB 8 in a test-tube add a 1 cm depth of dilute sulfuric acid. Then add a few drops of aqueous potassium manganate(VII). If no reaction is seen, place the test-tube in the hot water bath and leave to stand. To a 1 cm depth of FB 8 in a test-tube carefully add a small spatula measure of sodium hydrogen carbonate. [3] [Total: 18]

10 9701/32/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

11 9701/32/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

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CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2014 series 9701 CHEMISTRY 9701/32 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 32 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total 1 (a) PDO Layout 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 Recording 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 (not “difference”) unit: /cm3 or (cm3) or in cm3 or cm3 for each entry 1 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 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 have also been carried out. Do not award the mark if any ‘accurate’ burette readings (apart from initial 0) are given to zero dp. 1 All burette readings should be rounded to the nearest 0.05 cm3. Subtractions should be checked. The ‘best’ titres should be selected using the hierarchy: two (or more) identical, then two (or more) within 0.05 cm3 , then two (or more) within 0.1 cm3, etc. Examiner compares candidate mean titre with Supervisor mean titre. (a) MMO Quality V, VI and VII Award V, VI and VII for a difference from Supervisor, δ ≤ 0.20 cm3 Award V and VI for 0.20 < δ ≤ 0.30 cm3 Award V only for 0.30 < δ ≤ 0.50 cm3 Spread penalty: if the two ‘best’ titres are ≥ 0.50 cm3 apart cancel one of the Q marks. 3 [7]

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 32 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total (b) MMO Decisions Candidate must average two (or more) titres that are 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 calculates 1000 0.100 × (b) in (i) and gives ans (i) × 40 in (iii) (both answers to 3 or 4 sf) 1 PDO Display II Gives correct equation in (ii) H+ + HCO3 – → H2O + CO2 (allow H2CO3) 1 [2] Qn 1 Total 10

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 32 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total 2 (a) PDO Display I Shows clearly mass of empty crucible, mass of crucible + FB 3, mass of crucible and residue with correct units. (mass/g or (g) or in g) 1 Recording II Records all weighings consistently to at least 1 dp and records the correctly calculated mass of FB 3 used and water lost. Units must be correct and headings must be unambiguous. 1 MMO Quality Calculate mass of water lost/mass of FB 3 to 2 dp and compare with Supervisor value. Award III and IV if δ ≤ 0.05 Award IV only if 0.05 < δ ≤ 0.08 2 [4] (b) (i) ACE Interpretation I 18 lost water mass (expression) or correct moles of water Final answer must be to 2 to 4 sf 1 II moles of water divided by 10 or correct answer 1 III Mr in (ii) from mass/ans (i) 1 (ii) IV Calculates Ar of M Ar = 2 240 r − M 1 (iii) Conclusion V Choice of identity of M corresponds to nearest Ar 1 [5] (c) ACE Interpretation 0.1 or 0.2 for 1 dp balance, 0.01 or 0.02 for 2 dp balance, 0.001 or 0.002 for 3 dp balance in (i) and water of mass 100 × (i) in (ii) (expression or correct answer) 1 [1] (d) ACE Improvement Problem and appropriate improvement required. Not all the water was lost (1) so heat to constant mass (1) Water was regained on cooling (1) so cool in a desiccator/ with a lid (1) Use a balance with more dp (1) this gives a lower percentage error (1) The solid frothed/spat on heating (1) so use a deeper crucible/heat even more gently (1) Small amount of solid used gives high percentage error (1) use more solid. 2 [2] Qn 2 Total [12]

Page 5 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 32 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total FB 4 is MgSO4; FB 5 is C6H12O6(aq) reacts as ethanal; FB 6 is H2O reacts as propanone; FB 7 is C2H5OH; FB 8 is HCOOH(aq) 3 (a) (i) MMO Decisions I Selects NaOH and NH3, and uses each in excess. 1 PDO Layout II Unambiguous layout of all 4 observations. 1 MMO Collection III White ppt with NaOH and insoluble in excess. 1 IV White ppt with NH3 and insoluble in excess. 1 ACE Conclusion V Mg2+ 1 (ii) MMO Decisions Collection VI Selects barium chloride/barium nitrate and hydrochloric/ nitric acid. VII White ppt. 1 1 OR VI selects acidified potassium manganate(VII) VII no reaction/stays purple/purple solution formed OR VI add a named acid and test for sulfur dioxide VII negative test ACE Conclusion VIII SO4 2– 1 [8] (b) (i) MMO Collection I FB 5 and Tollens’: silver mirror/black or brown or grey ppt 1 II FB 7 and manganate(VII): colour change purple to colourless/decolourised 1 III No reaction for FB 6 with both reagents and FB 7 with Tollens’ 1 (ii) ACE Conclusion IV FB 6 is propanone (with no reactions observed) 1 V FB 5 and FB 7 identified 1 (iii) MMO Decisions VI Selects 2,4-DNPH 1 ACE Conclusion VII Red/orange/yellow ppt for FB 5 and FB 6 and no change for FB 7 ecf from identities in (ii) 1 [7]

Page 6 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 32 © Cambridge International Examinations 2014 Question Sections Indicative material Mark Total (c) MMO Collection Decolourises KMnO4 Effervescence/fizzing/bubbles Turns limewater milky 1 1 1 [3] Qn 3 Total [18]