Cambridge A Level Chemistry 9701 — 2013 Oct/Nov Paper 3 · Variant 5

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 9701/35 Advanced Practical Skills 1 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_35/4RP © UCLES 2013 *1417984110* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/35/O/N/13 © UCLES 2013 For Examiner’s Use I II III IV V VI VII 1 You are provided with a solution of an organic acid which is known to be one of the following. methanoic acid, HCOOH propanoic acid, C2H5COOH pent-2-enoic acid, CH3CH2CH=CHCOOH The solution was made by dissolving 1.85 g of acid in 250 cm3 of solution. You are to suggest the identity of the acid by fi nding its relative molecular mass, Mr, using a titration method. FA 1 is the solution of the unknown organic acid. FA 2 is 0.100 mol dm–3 sodium hydroxide, NaOH. phenolphthalein indicator (a) Method ● Fill the burette with FA 2. ● Pipette 25.0 cm3 of FA 1 into a conical flask. ● Titrate FA 1 with FA 2 using phenolphthalein as 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 FA 2 added in each accurate titration. [7]

3 9701/35/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (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 FA 1 required … cm3 of FA 2 [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 hydroxide in the volume of FA 2 you have calculated in (b). moles of NaOH = … mol (ii) One mole of any of the organic acids reacts with one mole of sodium hydroxide. Calculate the concentration, in mol dm–3, of the acid in FA 1. concentration of the acid in FA 1 = … mol dm–3 (iii) Calculate the concentration, in g dm–3, of the acid used to make solution FA 1. concentration of the acid in FA 1 = … g dm–3 (iv) Using your answers to (ii) and (iii), calculate the relative molecular mass, Mr, of the acid in FA 1. Mr of the acid = …

4 9701/35/O/N/13 © UCLES 2013 For Examiner’s Use (v) Suggest which of the acids, methanoic, propanoic or pent-2-enoic acid, is present in FA 1. Acid present is … . (vi) Suggest a test that could be carried out to distinguish pent-2-enoic acid from methanoic acid and propanoic acid. Give the expected result of your test. test … expected result … [5] [Total: 13]

5 9701/35/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use I II III IV V VI 2 The formula of hydrated iron(II) sulfate is FeSO4.xH2O where x shows the number of moles of water of crystallisation. The value of x can be found by heating solid hydrated iron(II) sulfate to remove the water of crystallisation. FA 3 is hydrated iron(II) sulfate, FeSO4.xH2O. (a) Method Record all weighings, in an appropriate form, in the space below. ● Weigh and record the mass of the empty crucible. ● Tip the contents of the tube labelled FA 3 into the weighed crucible. Reweigh and record the mass of the crucible and FA 3. ● Use a pipe-clay triangle to support the crucible and contents on a tripod. ● Heat gently for about three minutes. ● Leave the crucible to cool for approximately five minutes. While you are waiting for the crucible to cool, start work on Question 3. ● When cool, reweigh the crucible with the residue. ● Reheat gently for three minutes, cool and reweigh the crucible until you are satisfied that all the water of crystallisation has been lost. It should not be necessary to reheat the crucible more than three times. [6]

6 9701/35/O/N/13 © UCLES 2013 For Examiner’s Use (b) (i) Calculate the mass of water lost and the mass of anhydrous iron(II) sulfate that remains after the heating process. mass of water lost = … g mass of anhydrous iron(II) sulfate = … g (ii) Determine the value of x in the formula of hydrated iron(II) sulfate, FeSO4.xH2O. (Ar : H, 1.0; O, 16.0; S, 32.1; Fe, 55.8) value of x = … [3] (c) A group of students carried out this practical and made their measurements correctly. The students calculated a value of 9 for x. The textbook value of x is less than 9. (i) Suggest an error in the practical procedure of the experiment that could account for this result and explain why this gives a value of x that is too high. … … … … (ii) Suggest a modifi cation that could be made to the experimental procedure to reduce this error. Explain why this modifi cation should give an answer for x that is closer to the textbook value. … … … [3] [Total: 12]

7 9701/35/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 a solid FA 4. FA 4 is a mixture that contains two cations and two anions. (i) Place a spatula measure of FA 4 in a hard-glass test-tube. Heat the solid and identify the gas given off. Record all your observations. … … … (ii) To a spatula measure of FA 4 in a test-tube, add a 1 cm depth of dilute nitric acid. Record your observations. … …

8 9701/35/O/N/13 © UCLES 2013 For Examiner’s Use (iii) To a spatula measure of FA 4 in a test-tube, add approximately a 2 cm depth of distilled water to make a solution. Divide the solution into two portions. To the fi rst portion, add a 1 cm depth of aqueous sodium hydroxide. Record your observations. … … To the second portion, add a few drops of aqueous silver nitrate, then add a 1 cm depth of dilute nitric acid. Record your observations. … … … (iv) Use your results from (i) to (iii) to identify two anions and one cation that are present in FA 4. anions present … and … cation present … (v) What further test could be carried out on FA 4 to confi rm the presence of the cation you suggested in (iv)? You should state the reagent to be used and the expected result. Do not carry out this test. … … (vi) To a spatula measure of FA 4 in a test-tube, add a 1 cm depth of distilled water to make a solution. To this solution, add a few drops of aqueous barium chloride or barium nitrate. Describe the appearance of the precipitate formed and state its identity. appearance of precipitate … identity of precipitate … [9]

9 9701/35/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (b) FA 5, FA 6, FA 7 and FA 8 are aqueous solutions each containing one of the ions Al 3+, Ca2+, Zn2+ and Pb2+. (i) Carry out the following tests. Record your observations in the spaces provided in the table. test observations FA 5 FA 6 FA 7 FA 8 To a 1 cm depth of solution in a test-tube, add a few drops of aqueous sodium hydroxide, then add excess aqueous sodium hydroxide. To a 1 cm depth of solution in a test-tube, add a few drops of aqueous ammonia, then add excess aqueous ammonia. To a 1 cm depth of solution in a test-tube, add a 1 cm depth of aqueous potassium iodide. (ii) Use the Qualitative Analysis Notes on page 10 to identify the cation present in each of the solutions. FA 5 is … , FA 6 is … , FA 7 is … , FA 8 is … [6] [Total: 15]

10 9701/35/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 9701/35/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. 9701/35/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 9701/35 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 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 35 © Cambridge International Examinations 2013 Question Sections Indicative material Mark 1 (a) PDO Layout MMO Collection PDO Recording MMO Decisions I Volume given for rough titre and accurate burette readings tabulated. (min of 2 × 2 box) II Initial and final burette readings recorded for rough titre and volume of FA 2 added recorded for each accurate titre and acceptable headings and units in the accurate section. Acceptable headings are initial (burette) reading / initial volume / first reading / start reading Final (burette) reading / final volume / 2nd reading / end reading Titre / volume used / volume added / FA 2 added.(not difference or change in) Acceptable units are / cm3 / in cm3 / (cm3) / cm3 by each reading. III All accurate burette readings recorded to nearest 0.05 cm3. 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) 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 2 titres within 0.1 cm3, a further titration is carried out which is > 0.1 cm3 from the closer of the 2 initial titres unless further titrations, within 0.1 of any others, have also been carried out. Do not award the mark if any accurate burette readings (apart from initial zero) are given as integer. 1 1 1 1

Page 3 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 35 © Cambridge International Examinations 2013 MMO Quality V, VI and VII All burette readings should be rounded to the nearest 0.05 cm3. Subtractions should be checked. Examiner then selects the ‘best’ titre using the hierarchy: two identical, titres within 0.05 cm3 etc. These best titres should be used to calculate the mean titre to the nearest 0.01 cm3. Award V, VI and VII for a difference from Supervisor ≤ 0.2 cm3. Award V and VI for a difference from Supervisor 0.2 < δ ≤ 0.3 cm3. Award V for a difference from Supervisor 0.3 < δ ≤ to 0.5 cm3. Spread penalty: if the two ‘best’ titres used by the Examiner are ≥ 0.50 cm3 apart, cancel 1 Q mark. 3 [7] (b) ACE Interpretation Candidate calculates the mean correctly. Candidate must take the average of two (or more) titres where the total spread is ≤ 0.2 cm3. Working must be shown or ticks must be placed next to the accurate titres selected. The mean should normally be shown to 2 dp, rounded to the nearest 0.01 cm3. Example 26.667 must be rounded to 26.67 and not 26.65 and 26.675 must be rounded to 26.68 and not 26.70. Two special cases where the mean may not be to 2 dp: Allow mean to 3dp 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 – should be 26.05) Do not award this mark if: The rough titre was used to calculate the mean. The candidate performed 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]

Page 4 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 35 © Cambridge International Examinations 2013 (c) ACE Interpretation PDO Display ACE Conclusions MMO Decisions I Correctly calculates moles of NaOH = (b) × 0.1 in (i) 1000 and (i) × 1000 in (ii) 25.0 II 1.85 × 4 = 7.40 (g dm–3) and (iii) in (iv) (ii) III All answers to 3 or 4 sf (minimum of 3 answers) IV Acid with nearest Mr. Conclusion must correspond to Mr. V Test – (aqueous) bromine / acidified KMnO4 / alkaline KMnO4. Expected result – decolorises / (goes) colourless) / decolorised / turns green. 1 1 1 1 1 [5] [Total: 13]

Page 5 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 35 © Cambridge International Examinations 2013 Question Sections Indicative material Mark 2 (a) PDO Layout PDO Recording MMO Quality I Records at least four different balance readings (including 2 after heating) in the correct space. II Gives all appropriate headings and units for all weighings. III All recorded balance readings consistent to at least 1 decimal place. IV Evidence of reheating to constant mass. For balances reading to 1 dp two masses must be identical. For 2 or 3 dp balances, two masses must be within 0.05 g. V and VI Examiner calculates water of mass residue mass to 3 significant figures. Award V and VI for a difference from Supervisor up to 0.10. Award V for a difference 0.10 < δ ≤ 0.30. 1 1 1 1 2 [6] (b) (i) (ii) ACE Interpretation PDO Display ACE Interpretation I Calculation of mass of water and iron(II) sulfate II Mrs of 18 and 151.9 / sum of Ars if correctly used III Calculation x = mass water × 151.9 mass FeSO4 × 18 (or 8.439 / ratio used for Q) and final answer to nearest integer. 1 1 1 [3]

Page 6 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 35 © Cambridge International Examinations 2013 (c) ACE Interpretation ACE Improvements Spitting / decomposition of anhydrous salt / stirring If value of x is too high, the final mass of solid must be too low/ some solid sticks to stirrer / crucible was wet and this water lost on heating / any statement that says that too much water is lost (free standing mark) Spitting – lid / larger container / heat more gently. Decomposition – practical suggestion to control temperature. No improvement possible for stirring losses (max 2) 1 1 1 [3] [Total: 12] FA 5 = Pb(NO3)2; FA 6 = CaCl2; FA 7 is Al(NO3)3; FA 8 is ZnSO4 3 (a) (i) MMO Collection Sublimes / OWTTE / white smoke / white gas Litmus paper to blue and ammonia evolved. 1 1 (ii) MMO Collection Fizzing / bubbles / gas turns limewater milky 1 (iii) MMO Collection Sodium hydroxide – no reaction. Silver nitrate – white precipitate and dissolves partly in nitric acid / does not dissolve in nitric acid / bubbles 1 1 (iv) ACE Conclusions Anions – CO3 2– and Cl – Cation – NH4 + 1 1 (v) MMO Decisions (Aqueous) sodium hydroxide gives ammonia on heating 1 (vi) MMO Collection White (precipitate) and barium carbonate. (ecf of barium sulfite if sulfite in (iv)) 1 [9]

Page 7 Mark Scheme Syllabus Paper GCE A LEVEL – October/November 2013 9701 35 © Cambridge International Examinations 2013 (b) (i) MMO Collection test observations FA 5 FA 6 FA 7 FA 8 sodium hydroxide excess white ppt ppt dissolves white ppt ppt remains white ppt ppt dissolves white ppt ppt dissolves ammonia excess white ppt ppt remains no reaction white ppt ppt remains white ppt ppt dissolves KI yellow ppt no reaction no reaction no reaction 1 mark for each correct vertical column or 1 mark for each horizontal row (max 3 marks) 4 (ii) ACE Conclusions FA 5 is Pb2+ , FA 6 is Ca2+, FA 7 is Al 3+, FA 8 is Zn2+. All correct scores 2 marks, 2 correct scores 1 mark. 2 [6] [Total: 15]