Cambridge A Level Chemistry 9701 — 2008 Oct/Nov Paper 3 · Variant 2

This document consists of 12 printed pages. SP (SC/KS) T56858/3 © UCLES 2008 [Turn over 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 are advised to show all working in calculations. 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. * 5 4 7 3 6 0 4 6 2 0 * CHEMISTRY 9701/32 Paper 32 Advanced Practical Skills October/November 2008 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions For Examiner’s Use 1 2 3 Total Session Laboratory

2 9701/32/O/N/08 © UCLES 2008 1 You are required to find the concentration in mol dm–3 of sodium thiosulphate, Na2S2O3, in solution FB 1. FB 1 contains sodium thiosulphate. FB 2 is potassium manganate(VII) containing 28.44 g dm–3 KMnO4. FB 3 is 1.0 mol dm–3 sulphuric acid, H2SO4. FB 4 is 10% potassium iodide containing 100 g dm–3 KI. You are also provided with starch indicator. Dilution of FB 2 (a) By using a burette measure between 41.00 cm3 and 42.00 cm3 of FB 2 into the 250 cm3 graduated (volumetric) flask labelled FB 5. Record your burette readings and the volume of FB 2 added to the flask in the space below. Make up the contents of the flask to the 250 cm3 mark with distilled water. Place the stopper in the flask and mix the contents thoroughly by slowly inverting the flask a number of times. Titration Fill a second burette with FB 1, the solution containing sodium thiosulphate. Use a measuring cylinder to transfer 10 cm3 of FB 3 and 10 cm3 of FB 4 into a conical flask. Pipette 25.0 cm3 of FB 5 into the conical flask containing the mixture of FB 3 and FB 4. The potassium manganate(VII) oxidises potassium iodide to iodine, I2. Titrate the liberated iodine with FB 1 as follows. Run the solution from the burette into the conical flask until the initial red/brown colour of the iodine becomes pale yellow. Then add 1 cm3 of the starch indicator and continue to add FB 1 drop by drop until the blue/black colour of the starch/iodine complex disappears, leaving a colourless solution. This is the end-point of the titration. Perform a rough (trial) titration and sufficient further titrations to obtain accurate results. Record your titration results in the space below. Make certain that your recorded results show the precision of your working. [6] For Examiner’s Use i ii iii iv v vi

3 9701/32/O/N/08 [Turn over © UCLES 2008 (b) From your titration results obtain a volume of FB 1 to be used in your calculations. Show clearly how you obtained this volume. The volume of FB 1 is …………….. cm3. [1] Calculations Show your working and appropriate significant figures in all of your calculations. (c) Calculate how many moles of KMnO4 are contained in the FB 2 run into the graduated flask. [A r: K, 39.1; O, 16.0; Mn, 54.9] ………………….. mol of KMnO4 are run into the graduated flask. Calculate how many moles of KMnO4 are then pipetted from the 250 cm3 graduated flask into the titration flask. ………………….. mol of KMnO4 are pipetted into the titration flask. Use this answer to calculate how many moles of iodine molecules, I2, are formed when the manganate(VII) ions react with an excess of iodide ions in the titration flask. MnO4 – + 8H+ + 5e– Mn2+ + 4H2O I–
 I2 + e– ………………….. mol of iodine molecules, I2, are formed in the reaction. Use this answer to calculate how many moles of sodium thiosulphate will react with the iodine molecules formed. 2S2O3 2– S4O6 2– + 2e–
 I2 + e– I– ………………….. mol of thiosulphate ions react with the iodine molecules formed in the reaction. For Examiner’s Use i ii iii iv v

4 9701/32/O/N/08 For Examiner’s Use © UCLES 2008 Calculate, to 3 significant figures, the concentration in mol dm–3 of the sodium thiosulphate, Na2S2O3, in FB 1. The concentration of sodium thiosulphate in FB 1 is ……………….. mol dm–3. [5] [Total: 12]

5 9701/32/O/N/08 [Turn over For Examiner’s Use © UCLES 2008 2 Read through the instructions before starting the experiment. The relative molecular mass, Mr, of a metal carbonate can be estimated by adding a weighed sample of the carbonate to a weighed excess of hydrochloric acid and measuring the mass of carbon dioxide evolved. The tubes labelled FB 6 and FB 7 each contain the solid carbonate X2CO3. FB 8 is 2.0 mol dm–3 hydrochloric acid. Method (a) Follow the instructions below to determine the mass of carbon dioxide given off when X2CO3 reacts with an excess of hydrochloric acid. • Use a measuring cylinder to transfer 75 cm3 of FB 8 into a 250 cm3 conical flask. • Weigh the flask and acid FB 8. • Weigh the tube labelled FB 6 which contains the carbonate X2CO3. • Tip the contents of the tube FB 6 into the acid in the flask, a little at a time. This prevents loss of acid as spray from the vigorous reaction. • When the reaction appears to be complete, swirl the flask and leave to stand for 2–3 minutes, then reweigh the flask and its contents. • Reweigh the tube FB 6 and any residual carbonate not added to the acid. • Rinse out and drain the flask. • Repeat the whole experiment using tube FB 7. In an appropriate form below record the following. • all measurements of mass made • the mass of the carbonate, X2CO3, added • the mass of carbon dioxide given off [mass of CO2 = (initial mass of flask + acid) + (mass of carbonate) – (final mass of flask + contents)] Results [4] i ii iii iv

6 9701/32/O/N/08 For Examiner’s Use © UCLES 2008 Calculations (b) From your results for each experiment calculate the mass of X2CO3 that would produce 1.0 g of CO2. With FB 6 …………………….. g of CO2 are given off from ………………… g X2CO3. 1.0 g of CO2 is given off from ………………… g X2CO3. With FB 7 …………………….. g of CO2 are given off from ………………… g X2CO3. 1.0 g of CO2 is given off from ………………… g X2CO3. [3] (c) For each experiment calculate the relative molecular mass, M r, of X2CO3. X2CO3(s) + 2HCl(aq) 2XCl(aq) + CO2(g) + H2O(l) [A r: C, 12.0; O, 16.0] M r of X2CO3 from the experiment with FB 6 is ………………………… . M r of X2CO3 from the experiment with FB 7 is ………………………… . [1] (d) Carbon dioxide is soluble in aqueous solutions and this can lead to an error in the molecular mass calculated. From your observations on carrying out the experiments suggest another significant source of error. Explain the effect this will have on the measurements made and the molecular mass calculated. … … … …[1]

7 9701/32/O/N/08 [Turn over For Examiner’s Use © UCLES 2008 (e) Some of the carbon dioxide given off in the reaction remains dissolved in the acid solution. Suggest how you might modify the experimental method described to reduce or eliminate this error. … … …[1] (f) Carry out the following instructions. • Half fill each of two test-tubes with distilled water and place the tubes in a test-tube rack. • To one test-tube add 1 spatula measure of powdered barium carbonate, BaCO3. • To the second test-tube add 1 spatula measure of X2CO3. • Stopper each test-tube and shake vigorously. • Half fill each of two boiling-tubes with FB 3, dilute sulphuric acid. • To one boiling-tube add 1 spatula measure of powdered barium carbonate, BaCO3. • To the second boiling-tube add 1 spatula measure of X2CO3. • Do not attempt to stopper or shake either of these boiling-tubes. Record your observations in the table below. BaCO3 X2CO3 water FB 3 dilute sulphuric acid It is suggested that sulphuric acid could be used in place of hydrochloric acid in experiments to determine the Mr of metal carbonates. Make use of your observations and your knowledge of the chemistry of barium, to explain why the use of sulphuric acid would not be appropriate if the carbonate is barium carbonate. … … … [2] [Total: 12]

8 9701/32/O/N/08 © UCLES 2008 3 FB 9, FB 10 and FB 11 are aqueous solutions, each containing one of the cations listed on page 11 of the qualitative analysis notes. You will react FB 9, FB 10 and FB 11 with aqueous sodium hydroxide, NaOH, and aqueous ammonia, NH3, to identify the cations present in each of these solutions. You will also perform tests to identify the anions present in FB 9 and FB 10. 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 Note that three of the cations listed on page 11 may give no precipitate with aqueous NaOH. 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. (a) Pour 1 cm depth of FB 9, FB 10 and FB 11 into separate test-tubes. Stand the tubes in a test-tube rack and add aqueous sodium hydroxide, NaOH, a little at a time until the reagent is in excess. Repeat the test with aqueous ammonia, NH3, as the reagent. Record your observations in an appropriate form below. [4] (b) Using the observations above it is not possible to identify a single cation for any of the solutions. Use your observations and the qualitative analysis notes on page 11 to identify, for each solution, two or three cations which could be present. FB 9 could contain the cations … FB 10 could contain the cations … FB 11 could contain the cations … . [2] i ii iii iv For Examiner’s Use

9 9701/32/O/N/08 [Turn over For Examiner’s Use © UCLES 2008 (c) Use the qualitative analysis notes on page 11 to select further reagents or tests to identify precisely which cation is present in each of FB 9, FB 10 and FB 11. Record in an appropriate form below, • details of the reagents to be used, • the tests to be carried out, • your observations when the additional tests are carried out. A boiling-tube must be used if any solution is to be heated. Conclusion FB 9 contains the cation ………….. FB 10 contains the cation ………….. FB 11 contains the cation ………….. [4] i ii iii iv

10 9701/32/O/N/08 For Examiner’s Use © UCLES 2008 (d) FB 9 and FB 10 each contain one anion which is either a sulphate or a halide. Use the qualitative analysis notes on page 12 to select appropriate reagents and tests to determine which anion is present in each solution. Record in an appropriate form below, • details of the reagents to be used, • the tests to be carried out, • your observations when the tests are carried out. Conclusion FB 9 contains the anion ………….. FB 10 contains the anion ………….. [6] [Total: 16] i ii iii iv v vi

11 9701/32/O/N/08 © UCLES 2008 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, NH + 4(aq) 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. insoluble in excess green ppt. 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. insoluble in excess off-white ppt. 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 9701/32/O/N/08 © UCLES 2008 2 Reactions of anions ion reaction carbonate, CO2– 3 CO2 liberated by dilute acids chromate(VI), CrO2– 4 (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 pale 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, NO– 3 (aq) NH3 liberated on heating with OH–(aq) and Al foil nitrite, NO– 2 (aq) NH3 liberated on heating with OH–(aq) and Al foil; NO liberated by dilute acids (colourless NO → (pale) brown NO2 in air) sulphate, SO2– 4 (aq) gives white ppt. with Ba2+(aq) or with Pb2+(aq) (insoluble in excess dilute strong acids) sulphite, SO2– 3 (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 sulphur dioxide, SO2 turns potassium dichromate(VI) (aq) 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 October/November 2008 question paper 9701 CHEMISTRY 9701/32 Paper 32 (Practical 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. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes must be read in conjunction with the question papers and the report on the examination. • CIE will not enter into discussions or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the October/November 2008 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 Skill Breakdown of marks Successful collection of data and observations 8 marks Quality of measurements and observations 4 marks Manipulation, measurement and observation 16 marks Decisions relating to measurements or observations 4 marks Recording data and observations 5 marks Display of calculation and reasoning 3 marks Presentation of data and observations 12 marks Data layout 4 marks Interpretation of data or observations and identifying sources of error 6 marks Drawing conclusions 5 marks Analysis, conclusions and evaluation 12 marks Suggesting improvements 1 mark Statement Bank MANIPULATION, MEASUREMENT AND OBSERVATION (MMO) Successful collection of data and observations (Collection) C1 Set up apparatus correctly C2 Follow instructions given in the form of written instructions or diagrams C3 Use apparatus to collect an appropriate quantity of data or observations, including subtle differences in colour, solubility or quantity of materials C4 Make measurements using pipettes, burettes, measuring cylinders, thermometers, and other common laboratory apparatus Quality of measurements or observations (Quality) Q1 Make accurate and consistent measurements and observations Decisions relating to measurements or observations (Decisions) De1 Decide how many tests or observations to perform De2 Make measurements that span a range and have a distribution appropriate to the experiment De3 Decide how long to leave experiments running before making readings De4 Identify where repeated readings or observations are appropriate De5 Replicate readings or observations as necessary De6 Identify where confirmatory tests are appropriate and the nature of such tests

Page 3 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 PRESENTATION OF DATA AND OBSERVATIONS (PDO) Recording of data and observations (Recording) R1 Present numerical data, values or observations in a single table of results R2 Draw up the table in advance of taking readings/making observations so that they do not have to copy up their results R3 Include in the table of results, if necessary, columns for raw data, for calculated values and for analyses or conclusions R4 Use column headings that include both the quantity and the unit and that conform to accepted scientific conventions R5 Record raw readings of a quantity to the same degree of precision and observations to the same level of data Display of calculation and reasoning (Display) Di1 Show their working in calculations, and the key steps in their reasoning Di2 Use the correct number of significant figures for calculated quantities Data layout (Layout) L1 Choose a suitable and clear method of presenting the data, e.g. tabulations, graph or mixture of methods of presentation L2 Use the appropriate presentation medium to produce a clear presentation of the data L3 Select which variables to plot against which and decide whether the graph should be drawn as a straight line or a curve L4 Plot appropriate variables on clearly labelled x- and y- axes L5 Choose suitable scales for graph axes L6 Plot all points or bars to an appropriate accuracy L7 Follow the ASE recommendations for putting lines on graphs

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 ANALYSIS, CONCLUSIONS AND EVALUATION (ACE) Interpretation of data or observations and identify sources of error (Interpretation) I1 Describe the patterns and trends shown by tables and graphs I2 Describe and summarise the key points of a set of observations I3 Find an unknown value by using co-ordinates or intercepts on a graph I4 Calculate other quantities from data, or calculate the mean from replicate values, or make other appropriate calculations I5 Determine the gradient of a straight line I6 Evaluate the effectiveness of control variables I7 Identify the most significant sources of error in an experiment I8 Estimate, quantitatively, the uncertainty in quantitative measurements I9 Express such uncertainty in a measurement as an actual or percentage error I10 Show an understanding of the distinction between systematic errors and random errors Drawing conclusions (Conclusions) Con1 Draw conclusions from an experiment, giving an outline description of the main features of the data, considering whether experimental data supports a given hypothesis, and making further predictions Con2 Draw conclusions from interpretations of observations, data and calculated values Con3 Make scientific explanations of the data, observations and conclusions that they have described Suggesting Improvements (Improvements) Imp1 Suggest modifications to an experimental arrangement that will improve the accuracy of the experiment or the accuracy of the observations that can be made Imp2 Suggest ways in which to extend the investigation to answer a new question Imp3 Describe such modifications clearly in words or diagrams

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 Breakdown of marks Question 1 Question 2 Question 3 Skill Total marks Statement Marks Successful collection of data and observations C 8 1 1 6 Quality of measurements and observations Q 4 2 2 0 Manipulation, measurement and observation (MMO) 16 marks Decisions relating to measurements of observations De 4 1 0 3 Recording data or observations R 5 1 3 1 Display of calculation and reasoning Di 3 3 0 0 Presentation of data and observations (PDO) 12 marks Data layout L 4 1 1 2 Interpretation of data or observations and identifying sources of error I 6 3 3 0 Drawing conclusions Con 5 0 1 4 Analysis, conclusions and evaluation (ACE) 12 marks Suggesting improvements Imp 1 0 1 0 Total 12 12 16

Page 6 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 Question 1 Supervisor’s Report Check all subtractions in (a). Use the titres, corrected where necessary, to select the “best average” titre to be used as an accuracy standard using the following hierarchy. • value of 2 identical titres • average of titres within 0.05 cm3 • average of titres within 0.10 cm3, etc. Calculate, correct to 2 dp, the titre if the Supervisor had diluted 41.50 cm3 of FB 2. Do not round calculated averages to nearest 0.05 cm3. This is given by the expression titre diluted vol 41.50 × Record this value on the Supervisor’s script and on all candidate scripts against the titration table. Candidate scripts Check and correct all subtractions as above. Examiner is to select best titre as above, (do not include values labelled rough unless crossed out or ticked/used by candidate) and calculate the scaled titre for 41.50 cm3 of FB 2. If no volume of FB 2 diluted has been given, assume candidate has used 41.50 cm3. Record the value against the titration table and calculate the difference to Supervisor. Question Sections Statement Indicative material Mark 1 (a) PDO Layout L1 (i) Records initial and final burette readings in each of the tables (If 50.00 cm3 is used as initial burette reading, treat as 0.00 cm3. Do not award (i) in this case or if 50.00 cm3 is given as a repeated final burette reading in the 2nd table) 1 PDO Recording R5 (ii) All accurate burette readings in the titration table recorded to nearest 0.05 cm3 Treat 1st titration as rough unless the candidate has crossed out a “rough” label or used the value in calculating the average 1 MMO Collection C2 (iii) Follows instructions – Dilutes 41.00 cm3 to 42.00 cm3 (uncorrected) of FB 2 1 MMO Decisions De5 (iv) Has two or more uncorrected titres within 0.1 cm3 Titres labelled “rough” may be included 1 MMO Quality Q1 Q1 Accuracy Award (v) and (vi) if difference from Supervisor’s value is 0.3 cm3 or less Award (v) only for a difference of 0.3+ cm3 to 0.6 cm3 2 [6]

Page 7 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 (b) ACE Interpretation I4 Candidate selects/calculates correct “average” from titre values within 0.2 cm3. Average must be calculated correct to 2dp or nearest 0.05 cm3 if burette read to 2dp/0.05 cm3. For burette readings, consistent to 1dp the average may be correct to 1 or 2 dp) 1 [1] (c) ACE Interpretation I4 I4 Award (i) for 158 28.44 1000 diluted vol × in 1st step Award (ii) for (× 2.5) in 1st equation step and for (× 2) in 2nd equation step 1 1 PDO Display Di1 (iii) Working shown in at least three of the first four steps Correct or incorrect combination of half- equations into an equation for the reaction counts as working 1 Di2 (iv) 3 or 4 significant figures given in each answer attempted for sections 1–4. A Minimum of two sections attempted is required before this mark can be awarded. 1 Di2 (v) Award one mark for titre 1000 4 step to Answer × correctly evaluated to 3 sig fig. (Examiner to check) Allow ±1 in 3rd sig fig. It may be necessary to check any calculation in which numbers have been “carried” in a calculator 1 [5] Qn 1 Total 12

Page 8 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 2 (a) PDO Layout L1 (i) 4 balance readings + mass of X2CO3 and mass of CO2 clearly shown for at least one of the two experiments 1 PDO Recording R1 (ii) single table incorporating balance readings for FB 6 and FB 7 or balance readings for the flask + mass of X2CO3 1 R4 (iii) table has correct headings and units Accept only: / g; (g); or mass of……… in grams If not included in heading every entry must be followed by g 1 R5 (iv) all of the balance readings recorded are consistent to 1 dp, 2 dp, etc. showing the precision of the balance used 1 [4] For FB 6 and FB 7 Examiners calculate (check and correct candidate working if necessary) • the mass of carbonate that reacted • the mass of carbon dioxide given off • mass of carbonate (to 2 dp) giving 1.0 g of carbon dioxide. ACE Interpretation I4 Accurately calculates to 1 or 2 decimal places the mass of X2CO3 giving 1.0 g of CO2 for FB 6 and FB 7 If the balance used reads to 2 dp the candidate must give an answer to 2 dp. 1 (b) MMO Quality Q1 Q1 Accuracy Award two marks for a difference up to 0.3 g in the mass of carbonate in FB 6 and FB 7 giving 1.0 g of CO2 Award one mark only for a difference of 0.3+ g to 0.6 g. Award no Q marks if any mass of CO2 is negative or any mass CO2 > corresponding mass of X2CO3 2 [3]

Page 9 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 (c) ACE Interpretation I4 Give one mark for using the following expression for either FB 6 or FB 7 44 dioxide carbon of mass s candidate' carbonate of mass s candidate' × or (candidate’s value in (b) × 44) This is a mark for using the correct expression and not a mark for the actual value calculated or for sig fig. Beware calculations leading to Ar of X 1 [1] (d) ACE Interpretation I7 Give one mark for identifying one of the following as the significant error • loss of acid spray • solid stuck to the sides of the flask • diffusion time for the CO2 Do not allow spillage as a source of error. Mark multiple answers (±), ignoring any true but irrelevant suggestions 1 [1] (e) ACE Improvements Imp1 Give one mark if the candidate states that loss of carbon dioxide can be reduced by one of the following • warming the solution (to expel dissolved gas) • saturating the acid with CO2 before starting the experiment • extended swirling or shaking • using a smaller volume of more concentrated acid • waiting a longer time before taking the final reading 1 [1]

Page 10 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 (f) MMO Collection ACE Conclusions C3 Con3 The candidate should observe: • BaCO3 insoluble in water (powder remains) • X2CO3 soluble in water (colourless/clear solution) • effervescence/fizzing/bubbling with X2CO3 and acid • more rapid reaction in acid for X2CO3 than BaCO3 accept comparison of effervescence including no apparent bubbling with BaCO3 and bubbling with X2CO3 Give the mark for three out of the four correct boxes providing at least one has a reference to evolution of gas with acid. Give one mark for formation of insoluble barium sulphate. or barium sulphate is a white precipitate 1 1 [2] Qn 2 Total 12 FB 9 is aqueous ammonium bromide (NH4Cl/NaBr), FB 10 is aqueous aluminium sulphate, FB 11 is aqueous lead(II) nitrate. Selection of reagents – Accept any of the following: • a named compound or a recognisable (but not necessarily correct) formula for the compound • aqueous ions, e.g. Ba2+(aq) • a solution containing a named ion Identification of unknowns – Accept either of the following: • a named compound (or ion) • a fully correct formula for the compound or ion Question Sections Statement Indicative material Mark 3 (a) PDO Layout L1 (i) Give one mark for presenting observations for all 6 tests in a clear fashion. 1 PDO Recording R1 (ii) Give one mark for a single table showing observation on adding of NaOH and NH3 and when the reagent is in excess where an initial precipitate has been formed. 1

Page 11 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 MMO Collection C3 (iii) Give one mark for observing initial white ppt for FB 10 and FB 11 and no ppt / no reaction / clear or colourless solution with FB 9 Observations for both reagents required Do not give this mark if any white ppt turns brown 1 C3 (iv) Give one mark for recorded precipitates soluble in excess NaOH and insol. in excess NH3 for FB 10 and FB 11. 1 [4] (b) ACE Conclusions Con2 Con2 Mark consequentially from observations of white or off-white precipitates (Ignore ions not listed in QA Notes) Give one mark for concluding that FB 9 contains two of: NH4 + or Ba2+ or Ca2+ (in low concentration). Give one mark for concluding that FB 10 and FB 11 could contain Pb2+ or Al 3+. Allow this conclusion from: (i) an off-white ppt, soluble in excess NaOH and insoluble in excess NH3 (ii) a white ppt sparingly soluble in NH3 For: white ppt insoluble in excess NaOH and excess NH3 accept a conclusion of Mg2+ and Mn2+. Allow Mn2+ from white ppt turning brown Accept Zn2+, from white ppt soluble in excess NaOH and excess NH3, for FB 10 or FB 11. Mn2+ or Mg2+ may also be selected as single ions from appropriate observations 1 1 [2]

Page 12 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 (c) MMO Decisions De6 Check the ions selected. Where one ion only has been selected for FB 9, FB 10, or FB 11 a further test is still required as confirmation. (i) Give one mark for warming the solution with NaOH and testing for ammonia to identify NH4 + ion Test must be described in method or observation or for the use of dichromate or chromate to identify Ba2+ or eliminate Ca2+ 1 De6 (ii) Give one mark for choosing one of the following to distinguish between Pb2+ and Al 3+ HCl – barium chloride is not suitable, KI – solution FB 4, H2SO4 – solution FB 3, dichromate (VI), K2Cr2O7, Cr2O7 2– (aq) chromate (VI), K2CrO4, CrO4 2– (aq) Use of K2Cr2O7/K2CrO4 or H2SO4 as a single reagent is sufficient providing Ba2+ is one of only two ions selected for FB 9 in (b) and the reagent has been added to all three of the solutions. 1 MMO Collection C3 (iii) Mark observations consequentially. The expected observations for possible combinations of reagents are given below. 1 Reagent FB 9 FB 10 FB 11 warm with NaOH NH3 gas liberated no change no change HCl no change no change white ppt (allow observations also from BaCl 2) no change white ppt ignore white ppt KI no change no change yellow ppt H2SO4 no change no change white ppt Cr2O7 2– / CrO4 2- no change no change yellow ppt

Page 13 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 ACE Conclusions Con2 (iv) Give one mark for identifying: NH4 + in FB 9 – if NH4 + is one of possible ions; or Ca2+ if Ca2+ / Ba2+ are selected ions. Al 3+ in FB 10 and Pb2+ in FB 11 (NO e.c.f. in this section) 1 [4] (d) MMO Decisions De6 (i) Give one mark for choosing BaCl2 / Ba(NO3)2 Pb(NO3)2 as one reagent and AgNO3 / Pb(NO3)2 as the other reagent. (Pb2+ not acceptable as sole reagent) 1 PDO Layout L1 (ii) Give one mark for tabulating tests performed and the observations in those tests or presenting this information in other clear format. 1 MMO Collection C3 (iii) Give one mark for appropriate observations with the first reagent (see below) 1 C3 (iv) Give one mark for appropriate observations with the second reagent (see below) 1 MMO Collection C3 (v) Give one mark for partial solubility or insolubility in NH3 of the silver halide ppt formed with Ag+ – if that reagent was used. 1 Reagent FB 9 FB 10 BaCl 2 / Ba(NO3)2 (addition of HCl not required) no change white ppt AgNO3 off-white or cream ppt no change followed by NH3(aq) partially soluble Pb(NO3)2 white ppt white ppt

Page 14 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9701 32 © UCLES 2008 ACE Conclusions Con2 (vi) Give one mark for concluding, from observations, that the anion in FB 10 is sulphate and the anion in FB 9 is bromide. Bromide ions cannot be identified if Ba2+/Pb2+ have been selected as the reagents. Allow the bromide conclusion from: (i) off-white or cream precipitate with Ag+ (ii) white ppt with Ag+ partially soluble or insoluble in NH3 Allow a conclusion of iodide from a yellow ppt with Ag+ although this will not have scored the observation mark 1 [6] Qn 3 Total 16