Cambridge A Level Chemistry 9701 — 2007 May/June Paper 3 · Variant 2

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. * 2 3 3 1 1 0 7 1 6 3 * This document consists of 11 printed pages and 1 blank page. SP (CW) T38779/4 © UCLES 2007 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level CHEMISTRY 9701/32 Paper 32 Practical Test May/June 2007 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Instructions to Supervisors Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/32/M/J/07 For Examiner’s Use © UCLES 2007 1 You are required to determine the concentration in g dm–3 of hydrated ammonium iron(II) sulphate, (NH4)2SO4.FeSO4.6H2O, in the solution FB 1. FB 1 contains hydrated ammonium iron(II) sulphate. FB 2 is 0.0120 mol dm–3 potassium manganate(VII), KMnO4. (a) Dilution of FB 1 By using a burette measure between 36.00 cm3 and 37.00 cm3 of FB 1 into the 250 cm3 graduated flask labelled FB 3. Record your burette readings and the volume of FB 1 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 2. Pipette 25.0 cm3 of FB 3 into a conical flask. Use a measuring cylinder to add approximately 10 cm3 of 1.0 mol dm–3 sulphuric acid, H2SO4, and titrate with FB 2 until the first permanent pink colour remains in the solution. Perform one 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] i ii iii iv v vi

3 9701/32/M/J/07 [Turn over For Examiner’s Use © UCLES 2007 (b) From your titration results obtain a suitable volume of FB 2 to be used in your calculations. Show clearly how you obtained this volume. [1] Calculations Show your working and appropriate significant figures in all of your calculations. (c) Calculate how many moles of KMnO4 were run from the burette during the titration. … mol of KMnO4 were run from the burette. Calculate how many moles of Fe2+ ions reacted with the KMnO4 run from the burette. MnO4 –(aq) + 5Fe2+(aq) + 8H+(aq) Mn2+(aq) + 5Fe3+(aq) + 4H2O(I) … mol of Fe2+ reacted with the KMnO4 run from the burette. Calculate the concentration, in mol dm–3, of Fe2+ in FB 3. Concentration of Fe2+ in FB 3 = … mol dm–3.

4 9701/32/M/J/07 For Examiner’s Use © UCLES 2007 Calculate the concentration, in mol dm–3, of Fe2+ in FB 1. Concentration of Fe2+ in FB 1 = … mol dm–3. Calculate, to 4 significant figures, the concentration of (NH4)2SO4.FeSO4.6H2O in FB 1 in g dm–3 . [Ar: Fe, 55.8; H, 1.0; N, 14.0; O, 16.0; S, 32.1] FB 1 contains … g dm–3 of (NH4)2SO4.FeSO4.6H2O. [5] (d) A student learns that the solution of the iron(II) salt has been prepared by dissolving the solid in distilled water that has absorbed air from the laboratory. Suggest a way in which the distilled water can be prepared and stored in the laboratory to ensure that it contains a minimum of dissolved air. … … …[1] (e) Estimate the error in reading a volume from a burette. smallest division on burette scale = … cm3 estimated error in reading a volume = ± … cm3 [1] (f) A titre value is obtained by the difference between final and initial burette readings. What is the maximum possible error in obtaining a titre reading? estimated maximum error in the titre = ± … cm3 [1] (g) During one titration a student reads the burette twice. Each reading has an error but the titre has no error. Explain how this can happen. … … …[1] [Total: 16] i ii iii iv v

5 9701/32/M/J/07 © UCLES 2007 [Turn over BLANK PAGE

6 9701/32/M/J/07 For Examiner’s Use © UCLES 2007 2 Read through the question before starting any practical work. You are required to determine the enthalpy change when citric acid reacts with an excess of sodium hydrogencarbonate. Citric acid, found in citrus fruit such as lemons and limes, is 2-hydroxypropane-1,2,3-tricarboxylic acid. CH2-CO2H I C(OH)-CO2H I CH2-CO2H FB 4 is 0.8 mol dm–3 citric acid. FB 5 is solid sodium hydrogencarbonate, NaHCO3. (a) Citric acid is a triprotic (tribasic) acid – one mole of the acid reacts with three moles of sodium hydrogencarbonate. Calculate the minimum mass of sodium hydrogencarbonate that will react with all of the acid in 50.0 cm3 of FB 4. [Ar: Na, 23.0; H, 1.0; C, 12.0; O, 16.0] mass of NaHCO3 = … g [1] (b) Method Follow the instructions below to determine the enthalpy change for the reaction. You will carry out the experiment twice. • Weigh the empty weighing bottle. • Weigh the bottle with between 11.5 g and 12.0 g, an excess, of FB 5. • Support the plastic cup in the 250 cm3 beaker and pipette into it 50.0 cm3 of FB 4. • Measure and record the steady temperature of the FB 4 in the plastic cup. • Add the FB 5 from the weighing bottle, a little at a time, to the plastic cup. • Stir and record the lowest temperature reached. • Reweigh the empty weighing bottle. In an appropriate form at the top of the next page record • all measurements of mass and temperature, • the temperature fall, ΔT. Empty and rinse the plastic cup. Repeat the experiment and calculate the mean value of ΔT.

7 9701/32/M/J/07 [Turn over For Examiner’s Use © UCLES 2007 Results The mean value of ΔT is … °C. [6] (c) Calculate the enthalpy change of reaction using the following expression. ΔHreaction = mean ΔT × 4.3 kJ mol–1 Your answer should include the appropriate sign. ΔHreaction = … kJ mol–1 [1] [Total: 8]

8 9701/32/M/J/07 For Examiner’s Use © UCLES 2007 3 You are provided with three solutions, FB 6, FB 7 and FB 8, each containing one cation and one anion. One or more of the solutions contains a halide ion. One or more of the solutions contains a sulphate or sulphite ion. Identification of the anions in FB 6, FB 7 and FB 8 (a) By reference to the Qualitative Analysis Notes on page 12 you are to select and use (i) one reagent to precipitate any halide ion that is present, (ii) a second reagent to confirm the identity of any halide ion present. Because the solutions are coloured you will need to remove traces of solution from the precipitates. Record the tests performed, the practical procedures used and the observations made for each of the solutions. Present this information as clearly as possible in a suitable format in the space below. Use your observations to identify any halide ions present in the solutions FB 6, FB 7 and FB 8 and state which ion is present in which solution. … … … … … [7] i ii iii iv v vi vii

9 9701/32/M/J/07 [Turn over For Examiner’s Use © UCLES 2007 (b) Select reagents and carry out tests (i) to show which of the solutions contains a sulphate ion or a sulphite ion, and (ii) to establish which of these ions is present. Record your tests and observations below. State which of the ions, sulphate or sulphite, is present in which of the solutions FB 6, FB 7 and FB 8 and explain how you reached this conclusion from your tests above. … … … [3] Identification of the cations in FB 6, FB 7 and FB 8 (c) Using aqueous sodium hydroxide and aqueous ammonia it is possible to identify two of the cations present and to draw some conclusions about the nature of the remaining cation. Carry out tests with these reagents, recording details of what you did and observed in a suitable format in the space below. [4]

10 9701/32/M/J/07 For Examiner’s Use © UCLES 2007 (d) Explain how your observations in (c) identify two of the cations present and which of the solutions contain those cations. The cation contained in solution FB … is … explanation … … … The cation contained in solution FB … is … explanation … … … What conclusion of a general nature about the third cation can you draw from your observations in (c)? … … … … … … [2] [Total: 16]

11 9701/32/M/J/07 © UCLES 2007 Key: [ppt. = precipitate.] 1 Reactions of aqueous cations reaction with NaOH(aq) NH3(aq) aluminium, Al3+(aq) white ppt. soluble in excess white ppt. insoluble in excess ammonium, NH4 +(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/M/J/07 © UCLES 2007 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 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, 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) sulphate, SO4 2– (aq) gives white ppt. with Ba2+(aq) or with Pb2+(aq) (insoluble in excess dilute strong acid) sulphite, SO3 2– (aq) SO2 liberated with dilute acids; gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acid) 3 Tests for gases gas test and test results ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 gives a white ppt. with limewater (ppt. dissolves with excess CO2) chloride, 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 May/June 2007 question paper 9701 CHEMISTRY 9701/32 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. 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 May/June 2007 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 – May/June 2007 9701 32 © UCLES 2007 Skill Breakdown of marks Successful collection of data and observations 8 marks Manipulation, measurement and observation 16 marks Decisions relating to measurements or observations 8 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

Page 3 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark 1 (a) (i) (ii) (iii) (iv) PDO Layout PDO Recording MMO Collection MMO Decisions Tabulates initial and final burette readings and volume added in each of the tables Tabulation may be vertical or horizontal. Ignore absence of units Do NOT award this mark if any final and initial burette readings are inverted or 50 is used as the initial burette reading Both burette readings in the dilution table and final and initial burette readings for all accurate titres in the titration table recorded to the nearest 0.05 cm3. Treat all titres as “accurate” unless labelled rough or trial Follows instructions – Rough plus sufficient accurate titrations Award this mark if there are three or more titres OR where two titres only have been recorded they are within 0.20 cm3 (neither labelled as rough). The first titre does not have to be labelled rough Has at least two uncorrected titres within 0.1 cm3 Accuracy (v) and (vi) Give 2 marks if difference to Supervisor is 0.3 or less Give 1 of these two marks for a difference of 0.3+ to 0.5 Give 0 marks for a difference greater than 0.5 [1] [1] [1] [1] [2] [6] (b) ACE Interpretation Candidate selects/calculates appropriate “average” from any uncorrected titre values within 0.20 cm3. [1] [1] (c) (i)(ii) (iii) (iv) (v) ACE Interpretation PDO Display Examiner checks each of the first four steps of the calculation. Award two marks if all steps are chemically correct. Withhold 1 mark for each chemical error – no negative marks. Count non-completed steps as chemical errors. step 1 0.0120 x 1000 titre step 2 x 5 step 3 25 1000 × step 4 diluted volume 250 × Working shown in each step attempted 3 or 4 significant figures in final answer given for each of the first four steps Answer to last section is correctly evaluated to 4 sf for (candidate’s value to 4th step x 392). (Answer may be from final answer to step 4 or using number carried on calculator). [2] [1] [1] [1] [5]

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark (d) ACE Improvement Candidate suggests heating solution to eliminate air OR suggests practical way of storing water without air re- dissolving • Storing in a full bottle (no air space) • Ignore and reference to vacuum (pump) [1] [1] (e) ACE Interpretation Smallest division correctly read from burette and error estimated at ½ smallest division Burettes are graduated at 0.1 cm3 [1] [1] (f) ACE Interpretation Doubles error in reading to get maximum possible error [1] [1] (g) ACE Conclusions Explains that errors are identical (in the same direction) (and cancel). [1] [1] [Total: 16]

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark 2 (a) MMO Decisions Calculates the minimum mass of NaHCO3 needed to give an excess. (10.08 g) Do not penalise rounding to 10.1 g if 10.08 has been shown in calculation [1] [1] (b) PDO Layout PDO Recording MMO Collection Tabulates all experimental readings: (mass of empty weighing bottle, mass of bottle + solid, mass of bottle + residual solid, initial temperature, final temperature) and ∆T. Single table covering both experiments Table has correct labels and units (only g and oC) All weighings recorded with consistent precision to at least 1 dp and all temperature readings recorded to 1 dp only Give one mark if difference between (all) candidate’s ∆T values, as calculated by the Examiner, is within 0.5 oC Give one mark if the difference between mean ∆T value for Supervisor and closer/closest ∆T value of candidate, as calculated by the Examiner, is within 0.5 oC [1] [1] [1] [1] [1] [1] [6] (c) ACE Interpretation Examiner calculates to 1 decimal place the mean ∆T value from the candidate’s ∆T values for each experiment. Give 1 mark if the candidate’s answer to (d) is within 1% of (examiner calculated mean ∆T x 4.3) and the correct sign (+) is given. [1] [1] [Total: 8]

Page 6 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark FB 6 is iron(III) chloride; FB 7 is chromium(III) iodide (CrCl3 / KI); FB 8 is cobalt(II) sulphate 3 (a) (i) (ii) (iii) (iv) (v) (vi) (vii) PDO Layout PDO Recording MMO Decisions MMO Collection ACE Conclusions Presents tests, techniques and observations clearly To gain this mark there should be some reference in the table to washing at least one precipitate All observations in a single table Selects silver nitrate or other soluble silver salt as reagent Addition of Ag+(aq) or a solution containing Ag+ or silver(I) ions is acceptable Uses (aqueous) ammonia with the silver halide precipitates Filters or decants to obtain ppt (as soln is coloured not easy to see ppt) Reference to separating precipitate and solution for at least one of FB 6 or FB 7 Records yellow ppt insoluble in ammonia with FB 7 and white ppt soluble in ammonia with FB 6 Uses observations to make consequential deductions as to halide ions present. Candidates should identify Cl – in FB 6 and I – in FB 7 (no halide in FB 8) but mark other halides correct providing observations are completely correct for these ions If AgNO3 and Pb(NO3)2 selected as reagents only points (i), (ii), (iii) and (v) can awarded [1] [1] [1] [1] [1] [1] [1] [7] (b) MMO Decisions MMO Collection ACE Conclusion Selects barium chloride or barium nitrate (Addition of Ba2+aq) or a solution containing Ba2+ or barium ions is acceptable] and hydrochloric (or nitric) acid as reagents not sulphuric acid Records white ppt with BaCl2, insoluble in acid for only FB 8 or White ppt with BaCl2 and no SO2 (gas turning dichromate(VII) green) when FB 8 tested with HCl. Uses observations to make consequential conclusion for sulphate or sulphite if the white precipitate with BaCl2 is observed to dissolve when acid is added Marks in this section may be awarded for testing a single solution providing Ag+(aq) has been added to all three solutions and the halides identified If sulphuric acid or an unspecified acid is added after BaCl2, one mark maximum can be awarded in the section for a white ppt insoluble in acid. No marks if the acid is added before BaCl2 [1] [1] [1] [3]

Page 7 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark (c) PDO Layout PDO Recording MMO Collection Tabulates observations [This table should show clearly rows/columns for NaOH and NH3 as reagents and FB6/FB7/FB8. The table does not need lines to be drawn – clearly laid out and headed blocks of text are acceptable] All observations reported to reagent added in excess Give one mark each for correct observations for TWO of the following FB 6 – (Fe3+), FB 7 (Cr3+), and FB 8 (Co2+). FB 6 – red-brown/(brown/rusty) ppt, insoluble in excess with both NaOH and NH3. FB 7 – grey-green ppt with NaOH and NH3. ppt soluble in excess NaOH (to give a dark green solution) ppt insoluble in excess NH3. FB 8 – blue ppt with NaOH, (possibly turning pink) or brown with excess of the reagent. The ppt is insoluble. Blue ppt with NH3, expected to be insoluble in excess reagent of concentration used but (possibly dissolving to form a yellow/brown solution). [1] [1] [1] [1] [4] (d) ACE Conclusions Correctly identifies and gives evidence for Fe3+ in FB 6 Minimum evidence – red-brown ppt with NaOH and with NH3 Cr3+ in FB 7 Minimum evidence – grey-green ppt with NaOH and with NH3 OR grey-green ppt with NaOH, soluble in excess to form a green solution Recognises transition metal cation from various colour changes of precipitates Where FB 8 is included as one of the identified ions (probably incorrectly as Cu2+) the transition metal cation may be awarded for Cr3+ from the colour of the precipitate with NaOH and NH3 [1] [1] [2] [Total: 16]