Cambridge A Level Chemistry 9701 — 2014 Oct/Nov Paper 3 · Variant 5

This document consists of 13 printed pages and 3 blank pages. [Turn over IB14 11_9701_35/4RP © UCLES 2014 *8733689660* 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 12 and 13. 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 October/November 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/O/N/14 © UCLES 2014 1 In this experiment you are to determine x in the formula of hydrated sodium carbonate, Na2CO3.xH2O, by titration. FA 1 is aqueous sodium carbonate, Na2CO3, containing 150.0 g of solid Na2CO3.xH2O in each dm3 of solution. FA 2 is 0.110 mol dm–3 nitric acid, HNO3. methyl orange indicator (a) Method Diluting the solution of FA 1 ● Pipette 25.0 cm3 of FA 1 into the 250 cm3 volumetric (graduated) 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 carbonate is FA 3. ● Rinse the pipette with distilled water. Titration ● Pipette 25.0 cm3 of FA 3 into a conical flask. ● Fill the burette with FA 2. ● Add several drops of methyl orange indicator to the conical flask. ● Carry out 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 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 FA 2 added in each accurate titration. [7] I II III IV V VI VII

3 9701/35/O/N/14 © UCLES 2014 [Turn over (b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. volume of FA 2 = … cm3 [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 nitric acid in the volume of FA 2 calculated in (b). moles of HNO3 = … mol (ii) Complete the equation below and include the missing state symbols. Na2CO3(aq) + HNO3(aq) → NaNO3 + CO2 + H2O (iii) Calculate the number of moles of sodium carbonate in 25.0 cm3 of solution FA 3. moles of Na2CO3 in 25.0 cm3 of FA 3 = … mol (iv) Calculate the number of moles of sodium carbonate in 250.0 cm3 of solution FA 3. moles of Na2CO3 in 250.0 cm3 of FA 3 = … mol

4 9701/35/O/N/14 © UCLES 2014 (v) Use the information on page 2 and your answer to (iv) to calculate the relative formula mass, Mr, of hydrated sodium carbonate, Na2CO3.xH2O. Mr of Na2CO3.xH2O = … (vi) Calculate the value of x in Na2CO3.xH2O. Give your answer to the nearest whole number. [Ar: H, 1.0; C, 12.0; O, 16.0; Na, 23.0] x = … [6] (d) (i) State the maximum error in any single reading of the burette. maximum error = … cm3 (ii) Calculate the maximum percentage error in the volume of FA 2 in your fi rst accurate titre. maximum percentage error = …% [1] [Total: 15]

5 9701/35/O/N/14 © UCLES 2014 [Turn over 2 In this experiment you will determine the enthalpy change, ∆H, for the dehydration of hydrated sodium carbonate to anhydrous sodium carbonate. Na2CO3.xH2O(s) → Na2CO3(s) + xH2O(l) In order to do this, fi rst you will determine the enthalpy changes for the reactions of anhydrous sodium carbonate and hydrated sodium carbonate with excess hydrochloric acid. Then you will use Hess’ Law to calculate the enthalpy change for the reaction above. FA 4 is anhydrous sodium carbonate, Na2CO3. FA 5 is hydrated sodium carbonate, Na2CO3.xH2O. FA 6 is 4.0 mol dm–3 hydrochloric acid, HCl. (a) Determination of the enthalpy change for the reaction of anhydrous sodium carbonate, FA 4, with excess hydrochloric acid. Method ● Support a plastic cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25 cm3 of FA 6 into the plastic cup. ● Record the initial temperature of the acid. ● Weigh the container with FA 4 and record the mass. ● Slowly add all the FA 4 to the acid in the plastic cup. Note that the reaction will be vigorous. Avoid inhaling any acid spray produced. ● Stir constantly until the maximum temperature is reached. Record the maximum temperature. ● Weigh the container from which you added FA 4 and record the mass. ● Calculate and record the mass of FA 4 used and the temperature rise. [3]

6 9701/35/O/N/14 © UCLES 2014 (b) Calculation (i) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm3 of solution by 1.0 °C.] energy produced = … J (ii) Calculate the number of moles of anhydrous sodium carbonate used. [Ar: C, 12.0; O, 16.0; Na, 23.0] moles of Na2CO3 = … mol (iii) Calculate the enthalpy change, in kJ mol–1, for the reaction below. Na2CO3(s) + 2HCl (aq) → 2NaCl (aq) + CO2(g) + H2O(l) enthalpy change for anhydrous Na2CO3 = … … kJ mol–1 sign value [3]

7 9701/35/O/N/14 © UCLES 2014 [Turn over (c) Determination of the enthalpy change for the reaction of hydrated sodium carbonate, FA 5, with excess hydrochloric acid. Method ● Support the second plastic cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25 cm3 of FA 6 into the plastic cup. ● Record the initial temperature of the acid. ● Weigh the container with FA 5 and record the mass. ● Slowly add all the FA 5 to the acid in the plastic cup. Note that the reaction will be vigorous. Avoid inhaling any acid spray produced. ● Stir constantly until the minimum temperature is reached. Record the minimum temperature. ● Weigh the container from which you added FA 5 and record the mass. ● Calculate and record the mass of FA 5 used and the temperature decrease. [2] (d) Calculation (i) Calculate the energy absorbed during this reaction. [Assume that 4.2 J are absorbed when the temperature of 1.0 cm3 of solution falls by 1.0 °C.] energy absorbed = … J (ii) Use your answer to 1(c)(vi) to calculate the number of moles of hydrated sodium carbonate, Na2CO3.xH2O, used. [Ar: H, 1.0; C, 12.0; O, 16.0; Na, 23.0] (If you were unable to calculate x in 1(c)(vi), you may assume that x = 8. Note: this is not the correct value.) moles of Na2CO3.xH2O = … mol

8 9701/35/O/N/14 © UCLES 2014 (iii) Calculate the enthalpy change, in kJ mol–1, for the reaction below. Na2CO3.xH2O(s) + 2HCl (aq) → 2NaCl (aq) + CO2(g) + (x + 1)H2O(l) enthalpy change for Na2CO3.xH2O = … … kJ mol–1 sign value [2] (e) Use your values for the enthalpy changes calculated in (b)(iii) and (d)(iii) to calculate the enthalpy change for the reaction below. Na2CO3.xH2O(s) → Na2CO3(s) + xH2O(l) Show clearly how you obtained your answer. (If you were unable to calculate the enthalpy changes, you should assume that the value in (b)(iii) is – 43.1 kJ mol–1 and the value in (d)(iii) is +32.8 kJ mol–1. Note: these are not the correct values.) enthalpy change = … … kJ mol–1 sign value [2] (f) A student suggested that the experiments carried out in (a) and (c) would be more accurate if double the volume of hydrochloric acid had been used, but with hydrochloric acid of concentration 2.0 mol dm–3, instead of 4.0 mol dm–3. State and explain whether or not you agree with the student’s suggestion. … … … [1] [Total: 13]

9 9701/35/O/N/14 © UCLES 2014 [Turn over 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.

10 9701/35/O/N/14 © UCLES 2014 (a) FA 7 and FA 8 are mixtures. Each mixture contains one cation and two anions from those listed on pages 12 and 13. Carry out the following tests and record all your observations in the table below. test observations FA 7 FA 8 (i) Place a spatula measure of FA 7 or FA 8 into a boiling tube, then add approximately 5 cm3 of dilute nitric acid using the measuring cylinder. (Do not use FA 2 as the dilute nitric acid.) Then add about 5 cm3 of distilled water and shake to mix the solution. Use a 1 cm depth of the solution obtained in a test-tube for each of tests (ii) – (v). No observation required. (ii) Add aqueous sodium hydroxide. Do not carry out this test. (iii) Add aqueous ammonia. Do not carry out this test. (iv) Add aqueous barium nitrate followed by dilute nitric acid. (v) Add aqueous silver nitrate followed by aqueous ammonia.

11 9701/35/O/N/14 © UCLES 2014 [Turn over (vi) Use your observations to identify the following ions. FA 7 contains cation … FA 7 contains anions … and … FA 8 contains anions … and … State and explain all the evidence for your identifi cation of the cation in FA 7. … … … [7] (b) FA 9 contains two cations from the list on page 12. (i) Transfer approximately half of the FA 9 into a hard-glass test-tube and heat gently at fi rst, and then strongly, until no further change is seen. Test with litmus papers while you are heating. Record all your observations below. … … … … … (ii) Carry out further tests that will enable you to identify both cations in FA 9. Describe your tests briefl y and state your observations. FA 9 contains cations … and … [5] [Total: 12]

12 9701/35/O/N/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

13 9701/35/O/N/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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® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 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 October/November 2014 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS / A Level – October / November 2014 9701 35 © Cambridge International Examinations 2014 Question Indicative material Mark Total 1 (a) 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 II Appropriate headings and units for accurate titration and volume FA 2 added recorded for each accurate titre. Headings should match readings. • initial / start (burette) reading / volume (not V or vol) • final / end (burette) reading / volume • titre or volume / FA 2 and used / added (but 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 IV 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 0.10 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 0.10 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 for Supervisor and candidate. Examiner then selects the “best” titre 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. 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 cm3 <δ Y 0.40 cm3 Award V only for a difference of 0.40 <δ Y 0.60 cm3 Spread penalty: if the ‘best’ titres are > 0.50 cm3 apart cancel one of the Q marks. 3 [7]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS / A Level – October / November 2014 9701 35 © Cambridge International Examinations 2014 (b) Calculation of mean • Candidate must average two (or more) titres where the total spread is <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, and be correctly rounded to the nearest 0.01 cm3. 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) Correct working shown 1000 titre mean 0.110× in step (i) 1 (ii) Balanced equation with added state symbols Na2CO3(aq) + 2HNO3(aq) → 2NaNO3(aq) + CO2(g) + H2O(l) 1 (iii) and (iv) Correctly calculates moles Na2CO3 (in 25 cm3) = 2 1 × (i) and moles Na2CO3 (in 250 cm3) = 10 × (iii) 1 (v) Correctly calculates Mr = 10 4 150.0 × ×(iv) or (3.75 / (iv)) Theoretical answer = 286 1

Page 4 Mark Scheme Syllabus Paper Cambridge International AS / A Level – October / November 2014 9701 35 © Cambridge International Examinations 2014 (vi) Correctly calculates x to the nearest integer. x = 18 106 − (v) Allow ecf 1 Answers to (i), (iii), (iv) and (v) shown to 3 or 4 sf. Minimum of 3 answers needed to qualify for the mark. All answers given must have correct sf. 1 [6] (d) (i) and (ii) 0.05 cm3 % = titre accurate 100 0.1× Allow any accurate titre to be used (but not the mean). 1 [1] [Total: 15] 2 (a) Correct headings and units • mass of container and FA 4 / solid • mass of container (empty / plus residue) • mass of FA 4 (used) • initial temperature / thermometer reading • maximum / highest temperature / final / thermometer reading / temp. / T • temperature rise 1 (a) and (c) All four weighings shown to same number of dp 1 (a) Check and correct subtractions of Supervisor and candidate. Calculate difference between (corrected) candidate’s and Supervisor’s temperature rise, δ. Award if δ ⩽ 1.0 °C If ∆T is < 6.5 °C only award if δ < 0.5 °C. 1 [3] (b) (i) Correctly calculates: energy produced = 25 × 4.2 × temp rise (to 2–4 sf) 1 (ii) Correctly calculates moles of FA 4 = 106 used mass Answer must be expressed to 2–4 sf 1

Page 5 Mark Scheme Syllabus Paper Cambridge International AS / A Level – October / November 2014 9701 35 © Cambridge International Examinations 2014 (iii) Correct expression: ∆H = – 1000 × (ii) (i) Negative sign must be shown in answer. Answer must be expressed to 2–4 sf 1 [3] (c) and (a) All four thermometer readings shown to .0 °C or .5 °C 1 Examiner calculates difference between (corrected) candidate’s and Supervisor’s temperature fall, δ. If δ <2.0 °C award one mark. If ∆T is <9.5 oC only award if δ < 1.5 °C. If ∆T is<6.5 oC only award if δ <1.0 °C. If ∆T is<3.5 oC only award if δ <0.5 °C. 1 [2] (d) (i) and (iii) Correct expressions Energy absorbed = 25 × 4.2 × temp fall and ∆H = + 1000 × (ii) (i) (sign needed in final answer) 1 (ii) Correct expression for number of moles No. of moles = r M 5 FA of mass where Mr = 106 + 18x (x is candidate’s own value, or 8) 1 [2] (e) Attempt at use of Hess’s law, either by cycle or reverse reaction 2 1 Correctly calculates ∆H(dehydration) ∆H = (d)(iii) – (b)(iii) 1 [2]

Page 6 Mark Scheme Syllabus Paper Cambridge International AS / A Level – October / November 2014 9701 35 © Cambridge International Examinations 2014 (f) Accept one of the following answers • Agree – acid spray is reduced (since reaction will be slower) / smaller T rise so less heat loss / larger volume so volume measurement more accurate • Disagree – smaller temperature change, so higher (percentage) error of reading / reaction slower so more heat loss. 1 [1] [Total: 13] FA 7 is Al2(SO4)3 + NaCl; FA 8 is MgCO3 + KI; FA 9 is (NH4)2Fe(SO4)2 3 (a) (i) Both observations with HNO3 recorded correctly FA 7 no reaction / no change / dissolves FA 8 fizzing or (gas) turns limewater milky 1 (ii) or (iii) FA 7 + NaOH: white ppt, soluble in excess or FA 7 + NH3: (faint) white ppt, insoluble in excess 1 (iv) FA 7 + Ba(NO3)2: white ppt (insoluble in acid) and FA 8 + Ba(NO3)2: no ppt / no change / no reaction 1 (v) FA 7 + AgNO3: white ppt, soluble in ammonia and FA 8 + AgNO3: yellow ppt, insoluble in NH3 All four correct observations required. 1

Page 7 Mark Scheme Syllabus Paper Cambridge International AS / A Level – October / November 2014 9701 35 © Cambridge International Examinations 2014 (vi) cation cation is aluminium / Al3+ and white ppt with NH3 insoluble in excess 1 anions FA 7 anions: sulfate and chloride / SO4 2– and Cl – FA 8 anions: carbonate and iodide / CO3 2– and I– All four identities correct = 2 marks Any 2 or 3 identities correct = 1 mark 1 1 [7] (b) (i) Any two observations correct = 1 mark Any three (or more) correct = 2 marks • FA 9 is (pale) green • steam / vapour / condensation / water / liquid • litmus turns blue • yellow / white / brown residue / formed • white smoke (produced on strong heating) • litmus turns red on strong heating 2 (ii) Uses NaOH as reagent 1 With NaOH or NH3 (dark / dirty) green ppt formed and Fe2+ identified. 1 With NaOH and heat gas / ammonia turns litmus blue and NH4 + identified 1 [5] [Total: 12]