Cambridge A Level Chemistry 9701 — 2011 May/June Paper 3 · Variant 5

This document consists of 15 printed pages and 1 blank page. DC (AC) 33660/4 © UCLES 2011 [Turn over * 7 7 7 9 3 3 6 9 0 9 * 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 14 and 15. 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 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 9701/35/M/J/11 © UCLES 2011 For Examiner’s Use You are to determine the percentage by mass of water in the borax crystals. Borax reacts with hydrochloric acid according to the equation. Na2B4O7(aq) + 2HCl (aq) + 5H2O(l) 2NaCl (aq) + 4H3BO3(aq) 1 FA 1 is an aqueous solution containing 38.10 g dm–3 of borax crystals. Borax has the formula, Na2B4O7.xH2O. FA 2 is 1.00 mol dm–3 hydrochloric acid, HCl. You are also provided with an indicator suitable for the titration of a strong acid and a weak base. The indicator provided is … (a) Method Dilution • Fill the burette with FA 2. • Run between 44.50 cm3 and 45.50 cm3 of FA 2 from the burette into the 250 cm3 graduated (volumetric) flask, labelled FA 3. • Make the solution up to the mark with distilled water. • Shake the flask to mix the solution of FA 3. In the space below record your burette readings and the volume of FA 2 added to the graduated flask. Titration • Fill a second burette with FA 3, the diluted hydrochloric acid. • Pipette 25.0 cm3 of FA 1 into a conical flask. • Add to the flask a few drops of the indicator provided. • Titrate the borax in the flask with FA 3 until the appropriate colour change is observed for the end-point. You should perform a rough titration. In the space below record your burette readings for this rough titration. The rough titre is ………………. cm3.

3 9701/35/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use • 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 3 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. 25.0 cm3 of FA 1 required ………….. cm3 of FA 3. [1] (c) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the concentration of hydrochloric acid, in mol dm–3, in the diluted solution, FA 3. The concentration of HCl in FA 3 was …………………… mol dm–3. (ii) Calculate how many moles of HCl were present in the volume of FA 3 calculated in (b). ……………….. mol of HCl I II III IV V VI VII

4 9701/35/M/J/11 © UCLES 2011 For Examiner’s Use (iii) Calculate how many moles of Na2B4O7 reacted with the HCl in (ii). Na2B4O7(aq) + 2HCl (aq) + 5H2O(l) 2NaCl (aq) + 4H3BO3(aq) The HCl run from the burette reacted with ………………….. mol of Na2B4O7. (iv) Calculate the concentration, in g dm–3, of Na2B4O7 in FA 1. [Ar: B, 10.8; O, 16.0; Na, 23.0] The concentration of Na2B4O7 in FA 1 is …………………. g dm–3. (v) Use your answer to (iv) and the information at the start of question 1 to calculate the percentage by mass of water in the borax crystals, Na2B4O7.xH2O. [Ar: H, 1.0; B, 10.8; O, 16.0; Na, 23.0] Borax crystals contain ……………. % water. [6] (d) The maximum error for a 25 cm3 pipette commonly used in schools is ±0.06 cm3. The maximum error in any single burette reading is ±0.05 cm3. Calculate the maximum percentage error in each of the following. (i) The volume of FA 1 pipetted into the conical flask. maximum percentage error in the pipetted volume = ……………………. %. (ii) The titre volume calculated in (b). maximum percentage error in titre volume = ……………………. %. [1] [Total: 15] I II III IV V VI

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6 9701/35/M/J/11 © UCLES 2011 For Examiner’s Use 2 Read through the question carefully before starting any practical work. Sodium carbonate, Na2CO3, • reacts exothermically with hydrochloric acid, • does not decompose when heated, • reacts with acids. CO3 2–(s) + 2H+(aq) H2O(l) + CO2(g) Sodium hydrogencarbonate, NaHCO3, • reacts endothermically with hydrochloric acid, • decomposes when heated, 2HCO3 –(s) H2O(g) + CO2(g) + CO3 2–(s) • reacts with acids. HCO3 –(s) + H+(aq) H2O(l) + CO2(g) You are to measure the temperature changes when samples of (i) sodium carbonate, (ii) sodium hydrogencarbonate, (iii) a mixture of sodium carbonate and sodium hydrogencarbonate, react with an excess of hydrochloric acid. FA 4 is sodium carbonate, Na2CO3. FA 5 is sodium hydrogencarbonate, NaHCO3. FA 6 is a mixture of sodium carbonate and sodium hydrogencarbonate. FA 7 is 3.0 mol dm–3 hydrochloric acid, HCl. Method (a) sodium carbonate • Support the plastic cup in a 250 cm3 beaker. • Use a measuring cylinder to transfer 50 cm3 of FA 7 into the plastic cup. • Measure and record the temperature of the acid in the cup. • Measure and record the mass of the container labelled FA 4, containing Na2CO3. • Carefully tip the sodium carbonate from the weighed container FA 4 into the hydrochloric acid in the plastic cup. Note: There will be vigorous effervescence. Do not breathe the vapour. Add the solid in small portions with constant stirring using the thermometer. • Record the highest temperature obtained. • Reweigh the container FA 4 with any residual sodium carbonate. Record the mass. • Empty and rinse the plastic cup and dry it using a paper towel. In the space at the top of the next page, record, in an appropriate form, • both balance readings and both temperature measurements, • the mass of sodium carbonate, m1, used in the experiment, • the temperature rise, ΔT1.

7 9701/35/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use [4] Calculate the rise in temperature for each gram of sodium carbonate used in the experiment. ΔT1 m 1 = + …………………………. °C g–1 sign value (b) sodium hydrogencarbonate • Support the plastic cup in a 250 cm3 beaker. • Use a measuring cylinder to transfer 50 cm3 of FA 7 into the plastic cup. • Measure and record the temperature of the acid in the cup. • Measure and record the mass of the container labelled FA 5, containing NaHCO3. • Carefully tip the sodium hydrogencarbonate from the weighed container FA 5 into the hydrochloric acid in the plastic cup. Note: There will be vigorous effervescence. Add the solid in small portions with constant stirring using the thermometer. • Record the lowest temperature obtained. • Reweigh the container FA 5 with any residual sodium hydrogencarbonate. Record the mass. • Empty and rinse the plastic cup and dry it using a paper towel. In the space below, record, in an appropriate form, • both balance readings and both temperature measurements, • the mass of sodium hydrogencarbonate, m2, used in the experiment, • the temperature fall, ΔT2. [2] Calculate the fall in temperature for each gram of sodium hydrogencarbonate used in the experiment. ΔT2 m 2 = – ……………………. °C g–1 sign value I II I II III IV

8 9701/35/M/J/11 © UCLES 2011 For Examiner’s Use (c) mixture of sodium carbonate and sodium hydrogencarbonate • Support the plastic cup in a 250 cm3 beaker. • Use a measuring cylinder to transfer 50 cm3 of FA 7 into the plastic cup. • Measure and record the temperature of the acid in the cup. • Measure and record the mass of a clean, dry, weighing-bottle or tube. • Add to the tube between 8.5 g and 9.5 g of the mixture FA 6. • Record the mass of the weighing-bottle or tube + FA 6. • Carefully tip the weighed mixture into the hydrochloric acid in the plastic cup. • Note: There will be vigorous effervescence. Add the solid in small portions with constant stirring using the thermometer. • Record the highest or lowest temperature obtained. • Reweigh the weighing-bottle or tube with any residual mixture. Record the mass. In the space below, record, in an appropriate form, • all balance readings and temperature measurements, • the mass of the mixture, m3, used in the experiment, • the temperature change, ΔT3. Make certain that your recorded temperature change carries an appropriate sign. [2] (d) Transfer the following data from parts (a), (b) and (c). (a) ΔT1 m 1 = + …………………………. °C g–1 (b) ΔT2 m 2 = – …………………………. °C g–1 (c) m3 = …………………………. g ΔT3 = …………………………. °C sign I II

9 9701/35/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use The masses of sodium carbonate and sodium hydrogencarbonate in the weighed sample of the mixture used in experiment (c) can be represented as follows. mass of sodium carbonate / g = W mass of sodium hydrogencarbonate / g = (m3 – W) Evaluate the following equation to determine a value for W. [ W × ΔT1 m 1 ] + [(m3 – W) × ΔT2 m 2 ] = ΔT3 The mass of sodium carbonate was ………………………… g. [1] (e) Use the information at the beginning of question 2 to outline an alternative method that could be used in a school laboratory to find the mass of sodium carbonate and the mass of sodium hydrogencarbonate in the mixture FA 6. … … … … [1] [Total: 10]

10 9701/35/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. FA 8, FA 9 and FA 10 are aqueous solutions each containing a sodium cation and a single anion which could be a nitrite, a nitrate or a halide. (a) By reference to the Qualitative Analysis Notes on page 15, select a single reagent that would enable you to identify any solution containing the nitrite ion, NO2 –. reagent … Use this reagent to test each of the solutions. Record your observations in the table below. State clearly where no reaction has been observed. solution observation FA 8 FA 9 FA 10 [2] (b) By reference to the Qualitative Analysis Notes on page 15, select one reagent that would show that a halide ion is present. reagent …

11 9701/35/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use Use this reagent to test each of the solutions. Record your observations in an appropriate form in the space below. Select another reagent to identify or confirm which halide ions are present in the solutions. reagent … Tick the appropriate statement about the use of this reagent. It is added to the tube already containing the first reagent. It is added to a fresh sample of solution. Use this reagent to identify or confirm which halide ions are present in the solutions and record your observations in an appropriate form in the space below. [3] (c) From the results in (a) and (b) state which anions have been identified in the solutions. Complete the following table. Place a cross in any box if no anion has been identified. solution FA 8 FA 9 FA 10 anion present [1] I II III

12 9701/35/M/J/11 © UCLES 2011 For Examiner’s Use FA 11 and FA 12 are aqueous solutions each containing one cation from those listed in the Qualitative Analysis Notes printed on page 14. (d) Use aqueous sodium hydroxide and aqueous ammonia in separate tests to identify the cation present in each of the solutions. You will also require some of the solution, FA 11, for tests in (f). Record the results of your experiments with sodium hydroxide and ammonia in an appropriate form in the space below. [3] (e) Identification of the cations in FA 11 and FA 12 Complete the table below. solution FA 11 FA 12 cation present What is the evidence from your observations in (d) that enables you to identify the cation present in each of the solutions? The evidence supporting the conclusion for the cation in FA 11 is … … The evidence supporting the conclusion for the cation in FA 12 is … … [2] I II III I II

13 9701/35/M/J/11 © UCLES 2011 For Examiner’s Use (f) Complete the following table. test observations (i) Pour 1 cm depth of FA 11 into a test-tube. Add 1 cm depth of aqueous potassium iodide. Divide this mixture into two parts for use in (ii) and (iii) (ii) To the first part of the mixture from (i) add a few drops of starch solution. (iii) To the second part of the mixture from (i) add aqueous sodium thiosulfate, a drop at a time, until no further change is observed. In part (i) and in part (iii) redox reactions have taken place. Complete the table below to show the ion or molecule which has been oxidised and the ion or molecule which has been reduced in each of these reactions. reaction the ion or molecule which has been oxidised reduced (i) (iii) [4] [Total: 15] I II III IV

14 9701/35/M/J/11 © UCLES 2011 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.]

15 9701/35/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

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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 9701/35 Paper 31 (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 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 35 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark 1 (a) PDO layout I Volume given for rough titre and accurate titre details tabulated Minimum of 2×2 “boxes” 1 MMO collection II Follows instructions – dilutes 44.50–45.50 cm3 FA 2 and records unambiguous initial and final burette readings and volume of FA 2 diluted and volume of FA 3 added for each titration. Headings should match readings. 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 III All accurate burette readings (initial and final) recorded to nearest 0.05 cm3 including dilution table Assess this mark on burette readings only, ignore volume of FA 3 added. 1 PDO recording IV has two titres within 0.10 cm3 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 any other has also been carried out. 1 Examiner to 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 0.10 cm3, etc., (ignore rough titre) For candidates and Supervisor scale titre for 45.00 cm3 FA 2 diluted. Calculate titre × 45.00/volume of FA 2 diluted to 2 dp Calculate difference in Supervisor and candidate scaled values and award “quality” marks as below. MMO quality Award V, VI and VII for a difference from Supervisor, δ 0.30 cm3 1 Award V and VI for 0.30 < δ 0.60 cm3 1 Award V only for 0.60 < δ 1.00 cm3 If “best” titres are 0.60 cm3 apart cancel one of the Q marks 1 [7]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 35 © University of Cambridge International Examinations 2011 (b) ACE interpretation Calculates the mean, correct to 2 decimal places from any accurate titres within 0.20 cm3. The third decimal place may be rounded to the nearest 0.05 cm3. A mean of exactly .x25 or .x75 is allowed but the candidate may round up or down 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. 1 [1] (c) ACE interpretation I Expression correct in step (i) volume diluted/250 × 1.00 1 II Correctly uses titre from (b)/1000 × ans to (i) in (ii) and ½ × ans to (ii) in (iii) 1 III ans to (iii) × 1000/25 × 201.2 in (iv) 1 IV Uses (38.10 – ans to (iv))/38.10 × 100 in (v) 1 PDO display V Working shown in all steps attempted and a minimum of 3 steps. (use of 2 in (iii), missing × 40 or Mr in (iv) gains the mark) (Working should be a step in the right direction) 1 VI 3 to 4 significant figures shown in final answer to all steps attempted – minimum of 3 steps 1 [6] (d) ACE interpretation Correctly evaluates: 0.06/25 × 100 or 0.24 % and 0.10/titre in (b) × 100 Answers must be given to at least 2 significant figures and correctly rounded for the significant figures shown. 1 [1] [Total: 15]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 35 © University of Cambridge International Examinations 2011 2 (a) PDO layout I All data presented clearly in all three sections. (6,6,7) 1 PDO recording II Has correct headings and units on page 7. 1 III All thermometer readings recorded to nearest 0.5 ˚C in each of the experiments 1 IV Each pair of balance readings consistent and to at least 1 decimal place 1 [4] (b) Examiner to calculate (corrected) ∆T1/m1 and ∆T2/m2 for Supervisor and candidate. Compare candidate value with the same value from the Supervisor report. Award Q marks on the closer value. MMO Award I and II for δ 0.10 °Cg–1 1 quality Award I only for 0.10 < δ 0.30 °Cg–1 1 [2] (c) MMO collection I Follows instructions – weighs between 8.5 and 9.5 g of FA 6 (mass bottle with FA 6 – mass bottle) 1 PDO layout II Check ∆m and ∆T are correct in (c) 1 [2] (d) ACE interpretation Examiner to check there is no obvious error in the evaluation of the expression, then award one mark for a mass of sodium carbonate between 2.5 and 3.5 g. 1 [1] (e) ACE improvements Give one mark for: suggesting weighing, heating and weighing again, or weighing, heating and measuring gas volume or giving an outline for a titration method using 2 indicators. 1 [1] [Total: 10]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 35 © University of Cambridge International Examinations 2011 FA 8 is NaCl(aq); FA 9 is NaNO2(aq); FA 10 is NaBr(aq); FA 11 is CuSO4(aq); FA 12 is MgSO4(aq) 3 (a) MMO decisions Selects any named acid 1 MMO collection Records brown gas with FA 9 and no reaction with FA 8 and FA 10 1 [2] (b) MMO decisions I Selects: (correct full name or formula) silver nitrate as first reagent, aqueous ammonia as second reagent, aqueous ammonia added to tube with Ag+, 1st box ticked (do not allow if Pb2+ used as 2nd reagent) or lead nitrate as first reagent, silver nitrate as second reagent, Ag+(aq) added to fresh sample, 2nd box ticked 1 MMO collection II If Ag+ used as 1st reagent Give one mark for white ppt with FA 8 and cream ppt with FA 10 If Pb2+ used as 1st reagent Give one mark for white ppt with FA 8 and FA 10 If FA 9 not previously identified then no change/no reaction/no ppt (ignore any yellow colouration of solution with Pb2+) 1 III If Ag+ used as 1st reagent (with NH3 as 2nd) Give one mark if white ppt with FA 8 is soluble in aqueous ammonia and cream ppt with FA 10 is insoluble or partially soluble in aqueous ammonia If Ag+ used as 1st reagent (with Pb2+ as 2nd) Allow observations marks If Pb2+ used as 1st reagent (with Ag+ as 2nd) Give one mark for white ppt with FA 8 and Ag+ and cream ppt with FA 10 and Ag+. Ignore observations for FA 9. 1 [3] (c) ACE conclusion Mark consequentially on observations; Give one mark for appropriate anions identified for FA 8, FA 9 and FA 10. (Allow from off-white or cream ppt for Br- + Ag+) 1 [1]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 35 © University of Cambridge International Examinations 2011 (d) PDO recording I Observations in a single table. All additions of NaOH(aq) and NH3(aq) shown to excess where there is an initial ppt 1 MMO collection II All observations correct for FA 11 (Blue ppt in each, blue ppt insoluble in excess NaOH, soluble in excess NH3 or forming/turning to a deep/dark blue solution) 1 III All observations correct for FA 12 (White ppt insoluble in each) 1 [3] (e) ACE conclusion I Mark consequentially to observations. Expected conclusion is Cu2+ in FA 11 and Mg2+ in FA 12 Allow Ca2+ from white ppt insoluble in excess NaOH and no ppt with NH3. 1 II Gives appropriate evidence for each ion in the conclusion. Minimum evidence required for the expected ions: Cu2+ Records a blue ppt with either of the reagents or deep blue solution with excess NH3. Mg2+ White ppt insoluble in excess NH3 (or in each of the reagents) 1 [2] (f) MMO collection I Blue, black, purple colour observed on adding starch in (ii) 1 II The brown (solution) or (brown) solution formed in (i) is decolourised/colour fades/paler or brown (solution) in (i) and white, off-white or light brown ppt recorded. 1 ACE conclusion Award III and IV for two correct pairs 1 Award III only for one correct pair Expected results (i) I– is oxidised, Cu2+ is reduced (ii) S2O3 2– is oxidised, I2 is reduced Mark horizontally or vertically. 1 [4] [Total: 15]