Cambridge A Level Chemistry 9701 — 2004 Oct/Nov Paper 3 · Variant 1

This document consists of 7 printed pages and 1 blank page. MML 6133 6/03 S66582/1 © UCLES 2004 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level CHEMISTRY 9701/03 Paper 3 Practical Test October/November 2004 1 hour 15 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Instructions to Supervisors. READ THESE INSTRUCTIONS FIRST Write your details, including practical session and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen in the spaces provided on the Question Paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. 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. You are advised to show all working in calculations. Use of a Data Booklet is unnecessary. Centre Number Candidate Number Name If you have been given a label, look at the details. If any details are incorrect or missing, please fill in your correct details in the space given at the top of this page. Stick your personal label here, if provided. For Examiner’s Use LABORATORY SESSION 1 2 TOTAL

© UCLES 2004 2 9701/03/O/N/04 For Examiner's Use 1 FA 1 is an aqueous solution containing 23.72 g dm–3 of sodium thiosulphate, Na2S2O3. FA 2 is a solution of an oxidant, X, containing 5.15 g dm–3 of X. FA 3 is a solution containing potassium iodide, KI. FA 4 is 1.00 mol dm–3 sulphuric acid, H2SO4. In the presence of acid, the oxidant X oxidises iodide ions to iodine. 1 mole of X produces 3 moles of iodine, I2 The iodine liberated can then be titrated with thiosulphate ions, S2O3 2–, to reduce the iodine back to iodide. 2Na2S2O3(aq) + I2(aq) →Na2S4O6(aq) + 2NaI(aq) You are to determine the relative molecular mass of the oxidant X. (a) Pipette 25.0 cm3 of FA 2 into a conical flask. Use the measuring cylinder provided to add an excess of iodide ions (approximately 10 cm3 of FA 3), and 10 cm3 of sulphuric acid, FA 4. Titrate the iodine produced in the conical flask with FA 1. As the titration proceeds the colour of the iodine in solution will diminish. The end-point is reached when the colour disappears and the solution becomes colourless. There is no need to add starch indicator to find the end-point. Record your results in Table 1.1. Repeat the titration as many times as you think necessary to obtain accurate results. Make certain that the recorded results show the precision of your practical work. Table 1.1 Titration of Iodine with FA 1 [2] + [6] Summary 25.0 cm3 of FA 2 produced sufficient iodine to react with … cm3 of FA 1. Show which results you used to obtain this volume of FA 1 by placing a tick () under the readings in Table 1.1. final burette reading / cm3 initial burette reading / cm3 volume of FA 1 used / cm3

You are advised to show full working in all parts of the calculations. (b) Calculate how many moles of sodium thiosulphate, Na2S2O3, were run from the burette during the titration. [Ar: Na, 23.0; S, 32.1; O, 16.0.] [2] (c) Calculate how many moles of iodine, I2, react with the sodium thiosulphate run from the burette. [1] (d) Calculate how many moles of oxidant X were placed in the titration flask at the beginning of the titration. [1] (e) Calculate the concentration, in mol dm–3, of the oxidant X in FA 2. [1] (f) Calculate the relative molecular mass, Mr, of the oxidant X. [2] [Total: 15] 3 9701/03/O/N/04 [Turn over For Examiner's Use © UCLES 2004

2 FA 5 contains two cations and one anion from the following list: (Al 3+, NH4+, Ba2+, Ca2+, Cr3+, Cu2+, Fe2+, Fe3+, Pb2+, Mg2+, Mn2+, Zn2+; CO3 2–, CrO4 2–, Cl –, Br–, I–, NO3 –, NO2 –, SO4 2–, SO3 2–.). In all tests, the reagent should be added gradually, with shaking after each addition. Record your observations in the spaces provided. Your answers should include G details of colour changes and precipitates formed, G the names of gases evolved and details of the test used to identify each one. You should indicate clearly at what stage in a test a change occurs. Marks are not given for chemical equations. No additional or confirmatory tests for ions present should be attempted. Candidates are reminded that definite deductions may be made from tests where there appears to be no reaction. 4 9701/03/O/N/04 For Examiner's Use © UCLES 2004 Test Observations [7] (a) To 2 cm depth of FA 5 in a test-tube, add 1 cm depth of aqueous silver nitrate. Leave the mixture to stand and continue with tests (b) to (e). (b) To 2 cm depth of FA 5 in a boiling-tube, add 4 cm depth of aqueous sodium hydroxide. Stir thoroughly with the glass rod provided. Filter the mixture and retain the filtrate for tests (c), (d) and (e). Observe the residue in the filter paper after it has been exposed to the air for a few minutes. (c) To 1 cm depth of the filtrate from (b) in a test-tube, add 2 cm depth of dilute nitric acid followed by aqueous silver nitrate. (d) To 1 cm depth of the filtrate from (b) in a test-tube, add 2 cm depth of dilute hydrochloric acid followed by aqueous barium chloride.

Use the information in the Qualitative Analysis Tables on pages 6 and 7 to identify the ions present in FA 5. The cations present in FA 5 are … and … The anion present in FA 5 is … [1] Which observations support your choice of these ions? … … [1] What is the identity of the solid formed and dissolved in test (f)? Give a reason. … … [1] [Total: 10] 5 9701/03/O/N/04 [Turn over For Examiner's Use © UCLES 2004 Test Observations (e) Place 1 cm depth of the filtrate from (b) in a boiling-tube and warm the tube gently. Take care as a solution containing sodium hydroxide may ‘bump’ on heating and eject hot corrosive sodium hydroxide. (f) Observe the mixture left to stand in test (a). Use a teat pipette to remove the solution from the precipitate formed, then add 2 cm depth of distilled water to wash the precipitate. Allow the precipitate to settle and again use a teat pipette to remove the solution. Dissolve the solid in 2 cm depth of dilute aqueous nitric acid. You may need to cautiously warm the mixture. Use this solution in the test below. Add dilute hydrochloric acid to the solid dissolved in nitric acid.

QUALITATIVE ANALYSIS NOTES [Key: ppt. = precipitate] 1 Reactions of aqueous cations [Lead(II) ions can be distinguished from aluminium ions by the insolubility of lead(II) chloride.] 6 9701/03/O/N/04 © UCLES 2004 aluminium, Al 3+(aq) ammonium, NH4+(aq) barium, Ba2+(aq) calcium, Ca2+(aq) chromium(III), Cr3+(aq) zinc, Zn2+(aq) copper(II), Cu2+(aq) iron(II), Fe2+(aq) iron(III), Fe3+(aq) lead(II), Pb2+(aq) magnesium, Mg2+(aq) manganese(II), Mn2+(aq) reaction with NaOH(aq) NH3(aq) white ppt. soluble in excess ammonia produced on heating no ppt. (if reagents are pure) green ppt. insoluble in excess green ppt. insoluble in excess white ppt. with high [Ca2+ (aq)] pale blue ppt. insoluble in excess blue ppt. soluble in excess giving dark blue solution white ppt. soluble in excess white ppt. insoluble in excess white ppt. insoluble in excess white ppt. insoluble in excess white ppt. soluble in excess white ppt. soluble in excess grey-green ppt. soluble in excess giving dark green solution red-brown ppt. insoluble in excess off-white ppt. insoluble in excess off-white ppt. insoluble in excess white ppt. insoluble in excess no ppt. no ppt. grey-green ppt. insoluble in excess red-brown ppt. insoluble in excess ion

© UCLES 2004 2 Reactions of anions 3 Tests for gases 7 9701/03/O/N/04 carbonate, CO3 2– chromate(VI), CrO4 2–(aq) chloride, Cl–(aq) bromide, Br–(aq) iodide, I–(aq) nitrate, NO3 –(aq) nitrite, NO2 –(aq) sulphate, SO4 2–(aq) sulphite, SO3 2–(aq) ion reaction CO2 liberated by dilute acids yellow solution turns orange with H+(aq); gives yellow ppt. with Ba2+(aq); gives bright yellow ppt. with Pb2+(aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)); gives white ppt. with Pb2+(aq) NH3 liberated on heating with OH–(aq) and Al foil, NO liberated by dilute acids (colourless NO →(pale) brown NO2 in air) gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq)); gives white ppt. with Pb2+(aq) NH3 liberated on heating with OH–(aq) and Al foil SO2 liberated with dilute acids; gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acid) gives yellow ppt. with Ag+(aq) (insoluble in NH3(aq)); gives yellow ppt. with Pb2+(aq) gives white ppt. with Ba2+(aq) or with Pb2+(aq) (insoluble in excess dilute strong acid) gas test and test result turns damp red litmus paper blue gives a white ppt. with limewater (ppt. dissolves with excess CO2) bleaches damp litmus paper ‘pops’ with a lighted splint relights a glowing splint turns potassium dichromate(VI) (aq) from orange to green ammonia, NH3 carbon dioxide, CO2 chlorine, Cl 2 hydrogen, H2 oxygen, O2 sulphur dioxide, SO2

BLANK PAGE University of Cambridge International Examinations is part of the University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. 8 9701/03/O/N/04

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary and Advanced Level MARK SCHEME for the November 2004 question paper 9701 CHEMISTRY 9701/03 Paper 3 (Practical Test), maximum raw mark 25 This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which Examiners were initially instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. Any substantial changes to the mark scheme that arose from these discussions will be recorded in the published Report on the Examination. 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 discussion or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the November 2004 question papers for most IGCSE and GCE Advanced Level syllabuses.

Grade thresholds taken for Syllabus 9701 (Chemistry) in the November 2004 examination. minimum mark required for grade: maximum mark available A B E Component 3 25 22 20 14 The thresholds (minimum marks) for Grades C and D are normally set by dividing the mark range between the B and the E thresholds into three. For example, if the difference between the B and the E threshold is 24 marks, the C threshold is set 8 marks below the B threshold and the D threshold is set another 8 marks down. If dividing the interval by three results in a fraction of a mark, then the threshold is normally rounded down.

November 2004 GCE A AND AS LEVEL MARK SCHEME MAXIMUM MARK: SYLLABUS/COMPONENT: 9701/03 CHEMISTRY Paper 3 (Practical Test)

Page 1 Mark Scheme Syllabus Paper A and AS LEVEL – NOVEMBER 2004 9701 3 © University of Cambridge International Examinations 2005 N.B. Boxed references within this marking scheme relate to the accompanying revised booklet of Standing Instructions Question 1 Supervisor’s results Check all subtractions in the titration Table 1.1. Select the titre average. Use the rules in Standing Instructions, Section (f) Record this value on the front of the Supervisor’s script and as a ringed value by the titration Table 1.1 on each candidate script. (b) Candidate’s results Check all subtractions in the titration Table 1.1. The subtraction of titration results labelled as rough need not be checked unless the candidate has included in the volume used to calculate the average. Check the candidate’s average using the rules in (g) and (h). See (i) for details of spread penalties and possible spread penalty if only one titre has been selected. See (h) for penalty if only one accurate titration has been performed. Tick (if accepting the candidate’s value) or correct this value, recording it by titration Table 1.1 on the script. Calculate the difference to the Supervisor’s ratio. Award accuracy marks for differences as follows: Accuracy mark Spread Penalty Mark Difference to Supervisor/cm3 Range used/cm3 Deduction 8 Up to 0.10 0.20+ to 0.25 1 7 0.10+ to 0.15 0.25 to 0.30 2 6 0.15+ to 0.20 0.30+ to 0.35 3 5 0.20+ to 0.25 0.35+ to 0.40 4 4 0.25+ to 0.30 0.40+ to 0.50 5 3 0.30+ to 0.40 0.50+ to 0.60 6 2 0.40+ to 0.60 0.60+ to 0.80 7 1 0.60+ to 0.80 Greater than 0.80 8 0 Greater than 0.80 8

Page 2 Mark Scheme Syllabus Paper A and AS LEVEL – NOVEMBER 2004 9701 3 © University of Cambridge International Examinations 2005 Deduct from the accuracy mark one mark for each of the following errors: (i) Any Initial and Final Burette reading transposed or 50 used as initial burette reading. (ii) Final burette readings in Table 1.1 (except for any titration recorded as Rough) not recorded to 2 decimal places or “impossible” burette readings (e.g. 23.47 cm3) recorded at any point in the tables. (iii) No two recorded (uncorrected) titres within 0.1 cm3. (iv) An incorrect average calculated or No selection of at least two titres for the calculation of the average shown (selected titres may be ticked or used in a calculation of the average.) or Error in subtraction in any accurate titre (any rough titre if included in selection of titres to calculate the average) THERE IS A MAXIMUM DEDUCTION OF TWO MARKS FROM THE ACCURACY MARKS. In all calculations, ignore evaluation errors if working is shown (b) Give one mark for calculating the correct concentration in mol dm-3 158.2 23.72 or 0.15 Do not give this mark if S = 32.0 has been used. Give one mark for 1000 titre x concentration in mol dm-3 calculated by candidate or Give one mark for 1000 23.72 x titre and one mark for this expression x 158.2 1 (one) (one) 2 (c) Give one mark for answer (b) x 2 1 1 (d) Give one mark for answer (c) x 3 1 1 (e) Give one mark for answer (d) x 25 1000 1

Page 3 Mark Scheme Syllabus Paper A and AS LEVEL – NOVEMBER 2004 9701 3 © University of Cambridge International Examinations 2005 (f) Give one mark for (e) to answer 5.15 or (d) to answer 0.025 x 5.15 and Give one mark for a fully correct answer within 1% of the value calculated by the examiner. Do not give this mark if there are ‘chemical’ errors in (b) to (f) even if these errors are self-cancelling. The mark may be given if 158 rather than 158.2 has been used for Mr of sodium thiosulphate, providing the final answer is within 1% of the examiner calculated value The correct answer is given by the expression: titre 5150 Record the examiner calculated value (ringed) as close as possible to the candidate value. Where the candidate has rounded a final answer, work with the more ‘accurate’ calculation. 2 Total for Question 1 15 2 FA 5 is a solution of iron(II) ammonium sulphate. Test Observations (a) To 2 cm depth of FA 5 in a test-tube add 1 cm depth of aqueous silver nitrate. Leave the mixture to stand and continue with tests (b) to (e). (b) To 2 cm depth of FA 5 in a boiling-tube, add 4 cm depth of aqueous sodium hydroxide. Stir thoroughly with the glass rod provided. Filter the mixture and retain the filtrate for tests (c), (d) and (e). Give one mark for a green precipitate. Do not allow grey-green or green qualified by any other colour Allow muddy green or dirty green 1 Observe the residue in the filter paper after it has been exposed to the air for a few minutes. Give one mark for orange, rusty, orange/brown, red/brown or brown colour (on precipitate standing in the filter paper) Do not allow red or brick-red. 1

Page 4 Mark Scheme Syllabus Paper A and AS LEVEL – NOVEMBER 2004 9701 3 © University of Cambridge International Examinations 2005 Test Observations (c) To 1 cm depth of the filtrate from (b) in a test-tube, add 2 cm depth of dilute nitric acid followed by aqueous silver nitrate. Give one mark for no reaction or no precipitate or colourless solution. (Ignore any slight white colouration of the solution) Do not allow if there is any reference to a precipitate. 1 (d) To 1 cm depth of the filtrate from (b) in a test-tube, add 2 cm depth of dilute hydrochloric acid followed by aqueous barium chloride. Give one mark for white precipitate on addition of barium chloride or if the white precipitate is called barium sulphate. This mark may be given if a white ppt, not related to BaCl2 in the answer is given in a second line of the observation. (Assume the first line refers to addition of HCl) 1 (e) Place 1 cm depth of the filtrate from (b) in a boiling-tube and warm the tube gently. Take care as a solution containing sodium hydroxide may ‘bump’ on heating and eject hot corrosive sodium hydroxide. Give one mark for a chemical test on the gas that shows ammonia is evolved. Accept alkaline colour change with specified indicator paper or white smoke (fumes) with concentrated hydrochloric acid. An answer that describes red litmus turning blue and mentions ammonia is acceptable. 1 (f) Observe the mixture left to stand in test (a). Give one mark for a white/off-white /cream/grey precipitate Do not allow silver or brown and Give one mark for the solution turning yellow or orange. Do not allow brown solution. 2

Page 5 Mark Scheme Syllabus Paper A and AS LEVEL – NOVEMBER 2004 9701 3 © University of Cambridge International Examinations 2005 Test Observations (f) Use a teat pipette to remove the solution from the precipitate formed, then wash the precipitate with distilled water. Remove and discard the ‘wash’ water then dissolve the solid in dilute aqueous nitric acid. You may need to cautiously warm the mixture. Use this solution in the test below. Add dilute hydrochloric acid to the solid dissolved in nitric acid. Give one mark for a white precipitate 1 Where a candidate has not earned a mark for a particular test because of an incomplete observation the mark may be awarded retrospectively if the observation is completed in the “Evidence” section of page 4. e.g. A white precipitate is recorded in (d). On page 4 the candidate says sulphate because white ppt formed with BaCl2 Candidate records red litmus turning blue in (e). On page 4 the candidate says ammonium salt as (ammonia) gas turns red litmus blue Give one mark for identifying the correct ions present: NH4 +, Fe2+, SO4 2- (Examiners must see appropriate if incomplete observations for these ions) 1 Give one mark for evidence (from the candidate’s tests) that supports each of the ions chosen by the candidate. 1 (This mark can be given for correct evidence supporting incorrect ions) The minimum evidence: for NH4 + is reference to ammonia or any reference to red litmus turning blue in (e) for SO4 2- is a white precipitate in (d) Give one mark for identifying the solid formed in (e) as silver. Do not give this mark if there is no appropriate justification 1 There are 11 marking points for Question 2. If a candidate scores all 11 points: Record the 11 marks in a circle, then cross out and replace with [10] MAX: Total for Question 2 [10] Total for Paper [25]