Cambridge A Level Chemistry 9701 — 2011 May/June Paper 3 · Variant 4

This document consists of 12 printed pages and 1 insert. DC (SJF) 33707/5 © UCLES 2011 [Turn over * 7 7 0 0 2 9 6 1 7 1 * UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level 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 fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. 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 Advanced Practical Skills May/June 2011 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Instructions to Supervisors For Examiner’s Use 1 2 3 Total Session Laboratory

2 9701/34/M/J/11 © UCLES 2011 For Examiner’s Use 1 You are to determine the concentration, in mol dm–3, of the aqueous sodium thiosulfate. To do this you will first produce iodine solution by reacting aqueous potassium iodide with aqueous potassium manganate(VII). In this reaction iodide ions are oxidised to iodine by manganate(VII) ions in acidic solution. 2MnO4 –(aq) + 10I–(aq) + 16H+(aq) → 2Mn2+(aq) + 5I2(aq) + 8H2O(l) You will then titrate the iodine with aqueous thiosulfate ions, in FB 1. 2S2O3 2–(aq) + I2(aq) → S4O6 2–(aq) + 2I–(aq) You are provided with the following. FB 1 is a solution of sodium thiosulfate, Na2S2O3, of unknown concentration. FB 3 is 0.0050 mol dm–3 potassium manganate(VII), KMnO4. FB 4 is 0.10 mol dm–3 potassium iodide, KI. FB 5 is 1.0 mol dm–3 sulfuric acid, H2SO4. starch indicator (a) Method Dilution • Fill the burette with FB 1. • Run between 45.50 cm3 and 46.50 cm3 of FB 1 from the burette into the 250 cm3 graduated (volumetric) flask, labelled FB 2. • Make the solution up to the mark with distilled water. • Shake the flask to mix the solution of FB 2. In the space below record your burette readings and the volume of FB 1 added to the graduated flask.

3 9701/34/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use Titration • Fill a second burette with FB 2, the diluted sodium thiosulfate. • Pipette 25.0 cm3 of FB 3 into a conical flask. • Using a 25 cm3 measuring cylinder, add about 10 cm3 of FB 4. • Using the same measuring cylinder, add about 10 cm3 of FB 5. • Titrate the mixture in the flask with FB 2 until the colour is pale yellow. • Add about 10 drops of starch indicator. A blue-black colour should be seen as the starch reacts with the remaining iodine. • Continue to add FB 2 until the blue-black colour just disappears leaving a colourless solution. You should perform a rough titration. In the space below record your burette readings for this rough titration. 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 an appropriate form below all of your burette readings and the volume of FB 2 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. The iodine produced by 25.0 cm3 of FB 3 required ……………… cm3 of FB 2. [1] I II III IV V VI VII

4 9701/34/M/J/11 © UCLES 2011 For Examiner’s Use (c) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate how many moles of MnO4 – were pipetted into the conical flask. ……………… mol of MnO4 – (ii) Calculate how many moles of I2 were produced from the number of moles of MnO4 – calculated in (i). 2MnO4 –(aq) + 10I–(aq) + 16H+(aq) → 2Mn2+(aq) + 5I2(aq) + 8H2O(l) ……………… mol of I2 (iii) Calculate how many moles of S2O3 2– reacted with the I2 in (ii). 2S2O3 2–(aq) + I2(aq) → S4O6 2–(aq) + 2I–(aq) ……………… mol of S2O3 2– (iv) Calculate how many moles of S2O3 2– were present in the 250 cm3 graduated (volumetric) flask. ……………… mol of S2O3 2– (v) Use your answer to (iv) and the volume of FB 1 that was diluted to calculate the concentration, in mol dm–3, of the original solution of sodium thiosulfate, FB 1. The concentration of Na2S2O3 in FB 1 was ……………… mol dm–3. [6] I II III IV V VI

5 9701/34/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use (d) The maximum error for a 25 cm3 pipette commonly used in schools is ±0.06 cm3. The maximum individual error in any single burette reading is ±0.05 cm3. Calculate each of the following. The maximum percentage error in the volume of FB 3 pipetted into the conical flask maximum percentage error in the pipetted volume of FB 3 = ……………… % The maximum percentage error in the titre calculated in (b) maximum percentage error in the titre volume = ……………… % [1] [Total: 15]

6 9701/34/M/J/11 © UCLES 2011 For Examiner’s Use 2 You are to investigate how the rate of the following reaction varies with the concentration of sodium thiosulfate, Na2S2O3. Na2S2O3(aq) + H2SO4(aq) → S(s) + Na2SO4(aq) + SO2(g) + H2O(l) The rate can be found by measuring how long it takes for the solid sulfur formed to obscure the printing on the insert provided. Care should be taken to avoid inhalation of SO2(g) that is given off during this reaction. FB 5 is 1.0 mol dm–3 sulfuric acid, H2SO4. FB 6 is 0.10 mol dm–3 sodium thiosulfate Na2S2O3. Read through the instructions carefully and prepare a table for your results on page 7 before starting any practical work. (a) Method • Using the 50 cm3 measuring cylinder transfer 45 cm3 of FB 6 into a 100 cm3 beaker. • Using the 25 cm3 measuring cylinder measure 10 cm3 of FB 5. • Tip the FB 5 into the FB 6 in the beaker and immediately start timing. • Stir the mixture once with a glass rod and place it on top of the printed insert. • View the printed insert from above so that it is seen through the mixture. • Record the time, to the nearest second, when the printing on the insert just disappears. • Empty and rinse the beaker. Shake out as much of the water as possible and dry the outside of the beaker. • You will repeat the experiment to find out how the time for the printing on the insert to disappear changes when a different volume of FB 6 is used. • Using the 50 cm3 measuring cylinder transfer 20 cm3 of FB 6 and 25 cm3 of distilled water into the 100 cm3 beaker. • Using the 25 cm3 measuring cylinder add 10 cm3 of FB 5 to the mixture and immediately start timing. • Stir the mixture once with a glass rod and place it on top of the printed insert. • View the printed insert from above so that it is seen through the mixture. • Record the time, to the nearest second, when the printing on the insert just disappears. • Select suitable volumes of FB 6 and distilled water for two further experiments to investigate the effect of volume of sodium thiosulfate on the time taken for the printing on the insert to just disappear. Calculate the values of 1/time, where time is in seconds, to an appropriate number of significant figures.

7 9701/34/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use In the space below, record, in an appropriate form, all measurements of volume, time, and your calculated values of 1/time. [5] (b) Why was the total volume of solution kept constant in the experiments? … … [1] (c) It may be assumed that the rate of reaction is proportional to 1/time. Draw a conclusion from your results about the relationship between the concentration of sodium thiosulfate used and the rate of reaction. Explain your answer. … … … [1] (d) In the four experiments, which value of the time measured had the greatest error? Explain your answer. … … … [1] (e) How could the procedure be adapted to find the effect of changing the concentration of acid on the rate of reaction? … … … [1] [Total: 9] I II III IV V

8 9701/34/M/J/11 © UCLES 2011 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 identified 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 full name or correct formula of the reagents must be given. There are two parts to this question. In the first part you will analyse three metal salts, FB 7, FB 8 and FB 9, to identify the cation in each. In the second part you will carry out a series of tests on a different salt, FB 10, to identify the anion. (a) FB 7, FB 8 and FB 9 each contain one of aluminium ions, lead ions or zinc ions. By reference to the Qualitative Analysis Notes on pages 11 and 12, select two appropriate reagents to perform tests to identify the cations present. reagent … Record the tests performed and the results of those tests in an appropriate form in the space below. [5] (b) From your observations, identify the cations present in FB 7, FB 8 and FB 9. State the minimum evidence to support each of your choices. FB 7 contains ………………………… cations. evidence … … I II III IV V

9 9701/34/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use FB 8 contains ………………………… cations. evidence … … FB 9 contains ………………………… cations. evidence … … [3] (c) You are provided with a solid sample of FB 10 which is a metal salt. Use this sample to perform the experiments described below. Record all your observations in the table. test observations (i) Place a spatula measure of solid FB 10 into a dry hard-glass tube. Hold the test-tube in a holder. Heat the test-tube gently at first and then very strongly for several minutes. Allow the test-tube to cool, and then half fill it with distilled water. Dissolve the solid residue. This is FB 11. Retain this for tests (iv) and (v). While you are waiting for the test-tube to cool, continue with experiment (c)(ii) and (iii). (ii) Pour a 2 cm depth of aqueous copper(II) sulfate in a test-tube. Add a spatula measure of solid FB 10. (iii) Pour a 2 cm depth of aqueous aluminium sulfate into a test-tube. Add a spatula measure of solid FB 10. I II III IV V

10 9701/34/M/J/11 © UCLES 2011 For Examiner’s Use test observations (iv) Pour a 2 cm depth of solution FB 11 into a test-tube. Add the same volume of aqueous barium chloride. Then, using a dropping pipette, add dilute hydrochloric acid until no further change is seen. (v) Pour 1 cm depth of FB 11 into a test-tube and add an equal depth of aqueous copper(II) sulfate. Transfer the contents of the test-tube into an evaporating dish and place it over a Bunsen burner on a tripod and gauze. Heat strongly until all the water has been driven off and no further change is seen. [5] (d) Consider your observations in (c) and answer the following questions. In each case, provide evidence from your observations to support your conclusions. (i) Identify the anion present in FB 11 and state evidence to support your choice. FB 11 contains the ………………………… anion. evidence … … (ii) Suggest what type of reaction occurs as FB 10 is converted into FB 11. … … (iii) Suggest an explanation for what you observed in (c)(iii). … … [3] [Total: 16]

11 9701/34/M/J/11 © UCLES 2011 [Turn over 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 9701/34/M/J/11 © UCLES 2011 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) sulfite, 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, Cl2 bleaches damp litmus paper hydrogen, H2 “pops” with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium dichromate(VI) from orange to green 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.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2011 question paper for the guidance of teachers 9701 CHEMISTRY 9701/34 Paper 32 (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 must be read in conjunction with the question papers and the report on the examination. • Cambridge will not enter into discussions or correspondence in connection with these mark schemes. Cambridge is publishing the mark schemes for the May/June 2011 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 34 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark 1 (a) PDO Layout MMO Collection PDO Recording MMO Decisions I Volume given for Rough titre and accurate titre details tabulated. Minimum of 2×2 “boxes”. II Follows instructions – dilutes 45.50–46.50 cm3 FB 1 and initial and final burette readings and volume of FB 2 added recorded for each accurate titre (on page 3) Headings should match readings. Ignore units. Acceptable headings: initial/final or 1st/2nd (burette) (reading)/(reading at) start/finish; volume added/used/ titre; or wtte [not “difference”] 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) III All accurate burette readings (initial and final) recorded to nearest 0.05 cm3 (Accurate titration & dilution tables) Assess this mark on burette readings only, ignore volumes of FB 1 and FB 2 added 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 0.1 cm3 a further titration is performed which is more than 0.10 cm3 from the closer of the initial two titres, unless a fourth titration, within 0.1 cm3 of the third titration (or first two) has also been carried out. 1 1 1 1 Round any burette readings to the nearest 0.05 cm3. Check and correct, if necessary, 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 Calculate candidate titre × added volume Supervisor added volume candidate Calculate difference in Supervisor and candidate scaled values and award “quality” marks as below. [If candidate has not recorded a volume diluted, use 46.00 cm3]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 34 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark MMO Quality V, VI and VII Award V, VI and VII for a difference from Supervisor within 0.20 cm3 Award V and VI only for 0.20 < δ 0.40 cm3 Award V only for 0.4 < δ 0.6 cm3 Apply spread penalty as follows: If titres selected (by Examiner) differ 0.60 cm3 cancel one of the Q marks 1 1 1 [7] (b) ACE Interpretation Calculates the mean, correct to 2 decimal places (third decimal place may be rounded up to the nearest 0.05 cm3) from any accurate titres within 0.20 cm3. A mean of exactly .x25 or .x75 is allowed but the candidate may round up to .x3 or .x8 or to the nearest 0.05 cm3. If ALL burette readings are given to 1 decimal place then the mean can be given to 1 decimal place if numerically correct without rounding. Mean of 24.3 and 24.4 = 24.35 (✓) Mean of 24.3 and 24.4 = 24.4 () Titres to be used in calculating the mean must be clearly shown – in an expression or ticked in the titration table. Allow ecf from subtraction error for titre 1 [1] (c) ACE Interpretation PDO Display I correctly evaluates 1.25 × 10–4 II, III, IV are awarded for the correct expression but with no extra steps or for the correct answer if no working shown. II answer to (i) × 2.5 (3.125 or 3.13 × 10–4) and answer to (ii) × 2 (6.25 × 10–4) III Answer to (iii) × 250/mean titre in (b) IV Answer to (iv) × 1000/volume diluted V Working shown in a minimum of 4 steps working must be in the right direction: (i) 0.005 × 25 (ii) indicate use of mole ratio (× 5/2 or 2/5) (If iodide used then × 5 or /5) (iii) use of × 2 or × 1/2 (If iodide used then × 2/2 not × 1) (iv) answer to (iii) × 250 or (iii)/mean titre (v) answer to (iv) and volume diluted used in denominator (vi) All final answers to steps to 3 or 4 sf (minimum of 3 steps) 1 1 1 1 1 1 [6] (d) ACE Interpretation (0.06/25) × 100 ( = 0.24%) and (0.10/titre in (b)) × 100 (only expressions needed) 1 [1] [Total: 15]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 34 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark 2 (a) PDO Recording MMO Decisions I Records volume of FB 6, t and 1/t unambiguously for the four experiments Do not award if t is not to the nearest second II Correct headings and units: volume (cm3) or /cm3 or volume in cubic centimetres/cm3; time (s) or /s or time in seconds/s; 1/time (s–1) or /s–1 or 1/time or rate in per second III Selects two volumes of FB 6 one between 25–30 cm3 and one between 35–40 cm3 and sufficient water to make the solutions up to 45 cm3 before adding acid or between 30–35 and 10–15 with corresponding volumes of water. 1 1 1 Examiner corrects any fractional times to the nearest second for 45 cm3 and 20 cm3 of FB 6 and calculates t20/t45 to 2 dp MMO Quality Award IV only if 1.90 t20/t45 2.60 Award IV and V if 2.10 t20/t45 2.40 1 1 [5] (b) ACE Conclusions Volume of FB 6 is directly proportional to its concentration (if total volume is constant) or to keep the concentration of FB 5 constant or to keep the depth constant 1 [1] (c) ACE Conclusions Rate of reaction is proportional to concentration of FB 6 (allow directly proportional) or increase in concentration increases rate or 1/t 1 [1] (d) ACE Interpretation Either shortest time as greatest percentage/ fractional error or longest time as greatest uncertainty in judging when printing is obscured 1 [1] (e) ACE Improvements Keep volume of thio/FB 6 constant, change volume of acid/FB 5 and (add water to) make total volume constant or use different concentrations of acid/FB 5 and keep the volume of it and the thio/FB 6 constant 1 [1] [Total: 9]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 34 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark FB 7 is Al2(SO4)3, FB 8 is Zn(NO3)2, FB 9 is Pb(NO3)2, FB 10 is anhydrous NaHCO3 3 (a) PDO Layout MMO Decisions MMO Collection Do not allow a dash for ‘no reaction’ except for FB 8 with 2nd reagent provided NH3 obs correct. I Unambiguous layout of all (six minimum unless as above) observations with the two reagents independent of reagents chosen II Chooses NH3 and KI/K2CrO4/H2SO4/HCl (allow sodium/potassium dichromate) III three white ppts with NH3 IV Three correct obs FB 7: ppt insol in excess NH3, FB 8: ppt soluble in excess NH3, FB 9: ppt insol in excess NH3 V three correct obs for a suitable reagent Expected obs: FB 7 and FB 8 no reaction, no change, no ppt, and FB 9 white or yellow ppt depending on reagent Allow obs mark if BaCl2 used as 2nd reagent: white ppt with FB 7, no ppt with FB 8 and white ppt or no ppt with FB 9. (If three reagents used mark obs for the two specified on ‘reagent’ line.) If any solutions appear to have been transposed, mark strictly as mark scheme. 1 1 1 1 1 [5] (b) ACE Conclusions FB 7 contains Al3+/aluminium (ions) as (white) ppt insoluble in excess NH3 and no reaction with 2nd reagent FB 8 contains Zn2+/zinc (ions) as (white) ppt soluble in excess NH3 FB 9 contains Pb2+/lead (ions) as ppt with 2nd reagent Only penalise missing charge once. If NaOH used as 2nd reagent allow 1st mark if both Al3+ & Pb2+ specified for FB 7 and FB 9, (FB 8 mark is still available) The evidence for FB 7 and FB 9 may come from a third reagent (if used) For ‘transposed’ solutions, if conclusions are valid for the obs given, a maximum of 2 marks may be awarded. If BaCl2 used and only white ppt with FB 7 then allow FB 7 as Pb2+. If two (white) ppts both unknowns should be Pb2+ or Al3+/Pb2+. 1 1 1 [3]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 34 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark (c) MMO Collection (i) Steam/water vapour/misty vapour/condensation/ droplets of liquid/water or lime water turns milky/cloudy white (ii) (pale) blue/green ppt/solid (ignore effervescence) (iii) effervescence/fizzing/bubbling (ignore any reference to ppt) (iv) white ppt and either effervescence (with acid) or (colourless) solution/ppt or solid dissolves (v) solid/ppt turns black/dark green/ darkens in 2nd box Allow is formed/changes to 1 1 1 1 1 [5] (d) ACE Conclusions (i) CO3 2– from limewater turning milky in any part of (c) or fizzing/effervescence with acid Allow SO3 2– from correct obs in (c)(iv) (ii) thermal decomposition or loss of water of crystallisation/dehydration (if CO2 not tested for) (iii) effervescence suggests Al3+(aq)/Al2(SO4)3 is acidic or FB 10 contains Ba2+ or Pb2+ (both needed) if white ppt recorded or CO2 (produced) as limewater turns milky/cloudy white/forms white ppt or endothermic if cooling noted in (c)(iii) 1 1 1 [3] [Total: 16]