Cambridge A Level Chemistry 9701 — 2007 Oct/Nov Paper 3 · Variant 2

This document consists of 12 printed pages. SP (SM/KS) T47240/1 © UCLES 2007 [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. * 7 7 3 5 4 3 6 3 1 0 * CHEMISTRY 9701/32 Paper 32 Practical Test October/November 2007 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Instructions to Supervisors For Examiner’s Use 1 2 Total Session Laboratory

2 9701/32/O/N/07 © UCLES 2007 1 Read through question 1 before starting any practical work. You are provided with the following reagents. FB 1, 1 mol dm–3 sulphuric acid, H2SO4 FB 2, 0.1 mol dm–3 potassium iodide, KI FB 3, 0.1 mol dm–3 sodium thiosulphate, Na2S2O3 FB 4, 0.1 mol dm–3 hydrogen peroxide, H2O2 starch solution distilled water In the presence of an acid, iodide ions are oxidised by hydrogen peroxide to iodine. H2O2(aq) + 2H+(aq) + 2I–(aq) → 2H2O(l) + I2(aq) The rate of reaction can be followed by timing the formation of a fixed amount of iodine in the solution. If sodium thiosulphate is present in the reaction mixture it reacts with the iodine formed and the solution remains colourless. I2(aq) + 2S2O3 2–(aq) → 2I–(aq) + S4O6 2–(aq) When all of the sodium thiosulphate present has reacted, iodine, I2, will appear in the solution producing an immediate blue colour with starch indicator. In a series of experiments where the concentration of a reagent is changed • 1/time can be used as a measure of rate, • the volume of the reagent used can be taken as a measure of its concentration providing the total volume of the mixture is kept constant in each experiment. The order of reaction with respect to hydrogen peroxide can be obtained by plotting a graph of log rate against log [H2O2]. order of reaction = gradient of straight line log [H2O2] log rate For Examiner’s Use

3 9701/32/O/N/07 [Turn over © UCLES 2007 (a) Method Experiment 1 • Fill the burette labelled FB 3 with FB 3 and the burette labelled FB 4 with FB 4. • Use the measuring cylinder labelled A to put the following solutions into a 250 cm3 conical flask: 20 cm3 of FB 2, potassium iodide, 20 cm3 of distilled water. • Add to the flask from the burette 1.00 cm3 of FB 3, sodium thiosulphate. • Add six drops of starch indicator to the mixture in the flask. • Run 20.00 cm3 of FB 4, hydrogen peroxide, from the second burette into a 100 cm3 beaker. • Use the measuring cylinder labelled B to add 20 cm3 of FB 1, sulphuric acid, to the hydrogen peroxide in the beaker. • Tip the contents of the beaker into the conical flask and immediately start a stop-clock or note the start time on a clock with a second hand. • Swirl the flask to mix the reagents. • Observe the solution and stop the clock or note the time when the solution suddenly turns blue. • Record the time taken to the nearest second. The time taken is … s. Experiment 2 • Empty, thoroughly rinse and drain the conical flask used in experiment 1. • Use the measuring cylinder labelled A to put the following solutions into the 250 cm3 conical flask: 20 cm3 of FB 2, potassium iodide, 35 cm3 of distilled water. • Add to the flask from the burette 1.00 cm3 of FB 3, sodium thiosulphate. • Add six drops of starch indicator to the mixture in the flask. • Run 5.00 cm3 of FB 4, hydrogen peroxide, from the second burette into a 100 cm3 beaker. • Use the measuring cylinder labelled B to add 20 cm3 of FB 1, sulphuric acid, to the hydrogen peroxide in the beaker. • Tip the contents of the beaker into the conical flask and immediately start a stop-clock or note the start time on a clock with a second hand. • Swirl the flask to mix the reagents. • Observe the solution and again stop the clock or note the time when the solution suddenly turns blue. • Record the time taken to the nearest second. The time taken is … s. [2] For Examiner’s Use

4 9701/32/O/N/07 For Examiner’s Use © UCLES 2007 (b) In experiment 1 you will have obtained the time taken for a ‘fast’ reaction and in experiment 2 the time taken for a ‘slow’ reaction. You are to repeat the experiment with further mixtures in which only the concentration of hydrogen peroxide is varied. In selecting the mixtures to be used you should consider • how many mixtures need to be used, • what concentrations of hydrogen peroxide should be used, • what range these concentrations should cover, • that only the concentration of hydrogen peroxide must change. Remember – you already have reaction times for two mixtures with different concentrations of hydrogen peroxide. In the space below prepare to record, in an appropriate form, the results of the experiments you will perform and the results of experiments 1 and 2. Your recorded results should include calculated values to enable you to plot log (1/time) against log (volume of FB 4). Carry out the additional experiments and record your results. [11] i ii iii iv v vi vii viii ix x xi

5 9701/32/O/N/07 [Turn over For Examiner’s Use © UCLES 2007 (c) Use the grid below to plot a graph of log (1/time) against log (volume of FB 4). Draw an appropriate straight line through the points plotted. [4]

6 9701/32/O/N/07 For Examiner’s Use © UCLES 2007 (d) Draw construction lines on your graph and obtain data from them to enable you to calculate the gradient of the graph. Calculate the gradient of the line drawn, which is the order of reaction with respect to hydrogen peroxide. The reaction is … order with respect to hydrogen peroxide, H2O2. [3] (e) In experiment 1 burettes and measuring cylinders were used to measure volume. A burette is graduated to 0.10 cm3 and is usually read to the nearest 0.05 cm3. A 25 cm3 measuring cylinder is graduated to 0.5 cm3. Estimate the error when measuring a volume of 20 cm3 in a 25 cm3 measuring cylinder. The error is ± ……………………… cm3. Use this answer and the information above to calculate the percentage error for each volume measurement made in experiment 1. Complete the table below. solution apparatus used volume / cm3 error / cm3 % error FB 1, FB 2, distilled water 25 cm3 measuring cylinder 20 FB 3 burette 1.00 FB 4 burette 20.00 Identify the most significant source of error in this experiment. … …[3]

7 9701/32/O/N/07 [Turn over For Examiner’s Use © UCLES 2007 (f) The experimental method can be modified to enable the rate of reaction with respect to iodide ions, I–, to be investigated. You will perform two further experiments using the method for experiment 1 in section (a). You will keep the concentration of hydrogen peroxide constant and reduce the concentration of iodide ions. First copy your reaction time from experiment 1 in section (a) into the table below. Then complete the table below to show the volumes of FB 2 and distilled water you will use in these two further experiments. Carry out each experiment as before and record the time taken in each case. volume FB 1 (H2SO4) / cm3 volume FB 2 (KI) / cm3 volume water / cm3 volume FB 3 (Na2S2O3) / cm3 volume FB 4 (H2O2) / cm3 reaction time / s experiment 1 in section (a) 20 20 20 1.00 20.00 experiment i 20 1.00 20.00 experiment ii 20 1.00 20.00 [1] (g) Use the experimental results from the three experiments to draw a conclusion as to how the rate of reaction is affected by changing the concentration of iodide ions. … … …[1] [Total: 25]

8 9701/32/O/N/07 For Examiner’s Use © UCLES 2007 2 The three solutions FB 5, FB 6, and FB 7 each contain one of the following. copper(II) chloride, CuCl 2 chromium(III) chloride, CrCl 3 nickel(II) sulphate, NiSO4 (a) Use information from the Qualitative Analysis Notes on page 12 to select a pair of reagents that you could use to determine which solution contains the sulphate ion. Carry out the tests and record, in the space below, the reagents used and the observations made. From these tests, solution FB … contains the sulphate ion. [3] (b) The solutions containing copper(II) and chromium(III) ions can be distinguished from one another by adding either aqueous sodium hydroxide or aqueous ammonia. Nickel(II) ions behave in a similar way to copper(II) ions with these reagents. Add NaOH(aq) and NH3(aq) separately to each of the solutions FB 5, FB 6 and FB 7. Record your observations in the space below.

9 9701/32/O/N/07 [Turn over For Examiner’s Use © UCLES 2007 From your observations in (a) and (b) identify the solutions containing copper(II) ions and chromium(III) ions. Solution … contains Cu2+. supporting evidence … … Solution … contains Cr3+. supporting evidence … … [5] (c) You are to perform the tests given in the table below on the solid FB 8 and to comment on the type of compound present in FB 8. Record details of colour changes seen, the formation of any precipitate and the solubility of any such precipitate 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 table. You should indicate clearly at what stage in a test a change occurs. Marks are not given for chemical equations. No additional tests should be attempted. test observations with FB 8 (i) To 2 cm depth of distilled water in a boiling-tube, add 1 spatula measure of FB 8. Warm to dissolve the solid and immediately add a 1 cm length of magnesium ribbon. (ii) To 1 cm depth of aqueous sodium hydroxide in a test-tube, add 1 spatula measure of FB 8. Stir the mixture, then add 2 cm depth of dilute hydrochloric acid. Stir the mixture, then add 3 cm depth of aqueous sodium hydroxide.

10 9701/32/O/N/07 For Examiner’s Use © UCLES 2007 test observations with FB 8 (iii) To 1 cm depth of ethanol in a boiling-tube, add 2 spatula measures of FB 8 and a few drops of concentrated sulphuric acid (CARE: corrosive). Heat the contents of the tube for 1-2 minutes, using the apparatus provided for heating a flammable liquid (CARE). Pour the contents of the tube into a 100 cm3 beaker full of water. From your observations, draw conclusions about the type of compound present in FB 8. … … … [7] [Total: 15]

11 9701/32/O/N/07 © UCLES 2007 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/07 © UCLES 2007 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 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 acid) sulphite, SO2– 3 (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 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 2007 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 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 – October/November 2007 9701 32 © UCLES 2007 Generic Mark Scheme 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 – October/November 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark Round all recorded times in Supervisor and candidate scripts to the nearest second. List on the Supervisor’s script the rounded times for experiments 1 and 2 for each candidate. 1 (a) MMO Collection Performs experiments and records times for each reaction. Follows instructions. Award this mark if the reaction time for experiment 2 is within 20% of that obtained for experiment 2 by the Supervisor (or the majority of candidates in the Centre). 1 1 [2] 1 (b) PDO Recording (i) Single table for all experiments performed. (Experiments 1 and 2 must be included; minimum for table is volume and time for experiments 1 and 2) A single table has no repetition of headings. (ii) Table has been drawn up in advance. (must have minimum of 4 experiments tabulated – does not have to include experiments 1 and 2) – volumes of FB 4 are sequential. Experiments 1 and 2 may be entered first or last. (iii) Table includes columns for volume of FB 4 or log(volume of FB 4), time, 1/t or log(1/t). Ignore other columns or if total volume in experiment ≠ 81 (iv) Ignore log columns All other columns correctly labelled with appropriate unit (2007 syllabus). Accept t but not T for time heading Accept cm3, dm3, s, s–1, 1/s as units for units accept: unit after solidus, unit in bracket or in words e.g. / cm3; (cm3) or volume in cubic centimetres but not volume cm3 If the unit is not included in the column heading, every entry in the column must have a unit. (v) All times recorded to nearest second 1 1 1 1 1

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark Accuracy Calculate (vol of FB 4 x time) for experiment 1 and the two additional experiments with greatest volume of FB 4. (Round all times to the nearest second) Record the Vt values against the appropriate experiment on the candidate’s script. 1 (b) contd. MMO Decisions (vi) At least 3 mixtures – in addition to experiment 1 and experiment 2. (vii)Volumes of FB 4 chosen are uniformly spaced over the whole range (viii) and (ix) Award both of these marks if two of the Vt values are within 10% of the larger of the closest pair. [Award point (ix) but not point (viii) for a difference of 10+% to 20%] (x) and (xi) Award both of these marks if candidate’s time for experiment 1 is within 10% of that obtained by the Supervisor. [Award point (xi) but not point (x) for a difference of 10+% to 20%] 1 1 2 2 [11] Where experiment 1 has been repeated, assess accuracy using the time on page 3. Use the value on page 4 when checking the graph. 1 (c) PDO Layout Ignore labels – check which numerical values have been plotted Ignore omission of negative signs; direction of numbers on axes etc. Plots a rate (1/t or (log 1/t)) on y-axis and a concentration (volume of FB 4 or (log volume of FB 4)) on x-axis If labels correct but numbers on scale indicate a different quantity do not award this mark Easy to use scales chosen with plotted points covering more than ½ of each available axis 1 1

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark 1 (c) contd. PDO Layout A point must be plotted for each experiment performed – take care where experiments 1 and 2 have been omitted from the main results table) All points plotted to within ½ small square and in the correct half of a small square Appropriate straight line drawn through the points. (This does not have to be a “best-fit” line but must show correlation to the points plotted. Do not award this mark if there is clearly a better line that could have been drawn through the points) A minimum of three points that lie close to the line are required – no anomalous point is permitted where three points only have been plotted. Do not award this mark if the line is drawn through points “bunched” in less than 20 x 20 small squares. 1 1 [4] If a candidate has only performed experiments 1 and 2 or if data has only been plotted for 2 experiments, points L4, L5 and L6 but not L7 can be awarded. 1 (d) PDO Display ACE Interpretation Construction lines drawn on the graph. The hypotenuse of the constructed “triangle” should cover at least half of the length of the line drawn by the candidate. Correctly reads (to nearest ½ small square) the coordinates from the graph Accept values from the table if the line is drawn through the point. Do not penalise reuse of values for an incorrectly plotted point Calculates gradient correctly to at least 1 decimal place using the values read from the graph by the candidate. 1 1 1 [3] Where data for two experiments only has been plotted, the Display marks only may be awarded. Do not award the Display mark for reading coordinates if either value is taken from the table.

Page 6 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark 1 (e) ACE Interpretation Give one mark for an error of ±0.25 cm3 when reading a 25 cm3 measuring cylinder Estimated and % errors 20 cm3 in 25 cm3 measuring cylinder: Correct % for error above. 1.00 cm3 in burette: single burette reading 0.05 cm3 or 0.10 cm3 two burette readings 5% or 10% 20.00 cm3 in burette: single burette reading 0.05 cm3 or 0.10 cm3 two burette readings 0.25% or 0.5% Consequential on calculations. Measuring 1.00 cm3 from burette should be most significant error. 1 1 1 [3] 1 (f) ACE Improvements Has: Volume of FB 4 < 20 cm3, variable volume of water, water to keep total combined volume (FB 4 and water) constant at 40 cm3. Record the volume of (FB 4 + water) for each experiment to the left of the table. 1 [1] 1 (g) PDO Display Uses experimental data to make appropriate comment, from experimental results, as to how rate varies with concentration of KI. [Do not give this mark where mixtures selected in (f) are not appropriate, i.e. the volume of (FB 4 + water) ≠ 40 cm3] Where an acceptable qualitative statement has been given ignore any incorrect attempt at a quantitative/mathematical expression. 1 [1] Qn 1 Total 25

Page 7 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark FB 5 is aqueous nickel(II) sulphate, FB 6 is aqueous copper(II) chloride, FB 7 is aqueous chromium(III) chloride, FB 8 is solid 2-hydroxybenzoic acid (salicylic acid) 2 (a) MMO Decisions MMO Collection ACE Conclusion Chooses BaCl2/Ba(NO3)2 and HCl/HNO3 (not H2SO4) as reagents Records white ppt with BaCl2, insoluble in HCl for FB 5 only (obs for FB 6 and FB 7 not required) If acid is not specified – give this mark only if barium salt is added before the acid Concludes that FB 5 contains the sulphate ion Allow deduction from addition of barium salt without addition of acid If no observations recorded this mark can be awarded if it is clear that the barium salt and appropriate acid are added to all three solutions. 1 1 1 [3] 2 (a) alt MMO Decisions MMO Collection ACE Conclusion Chooses AgNO3 and aqueous ammonia Records white ppt with AgNO3, soluble in aqueous ammonia for FB 6 and FB 7 (obs for FB 5 not required) Concludes that FB 5 contains the SO4 2– ion (by elimination) Allow deduction from addition of silver salt without addition of aqueous ammonia 1 1 1 2 (b) MMO Collection Give one mark for the following observations on adding NH3 NaOH FB 5 green ppt green ppt FB 6 blue ppt blue ppt FB 7 grey-green ppt grey-green ppt Give one mark for the following observations on adding excess reagent (excess is needed in recorded observation except where no ppt is recorded, correctly or incorrectly, on first addition of reagent) NH3 NaOH FB 5 (soluble) insoluble – blue solution FB 6 (soluble) insoluble – dark blue solution FB 7 insoluble (soluble) – dark green solution Where only one reagent has been used, one of the C3 marks above may be awarded for fully correct observations on adding the reagent to excess. 1 1

Page 8 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 32 © UCLES 2007 Question Sections Indicative material Mark 2 (b) contd ACE Conclusions ACE Interpretation FB 7 contains Cr3+ FB 6 contains Cu2+ Gives appropriate evidence for identification of the ions Minimum evidence for Cu2+ blue ppt with NaOH and with NH3(aq) or dark blue solution with excess NH3(aq) Minimum evidence for Cr3+ grey-green ppt with NaOH and with NH3(aq) or dark green solution with excess NaOH 1 1 1 [5] 2 (c) (i) (ii) (iii) MMO Decisions MMO Collection MMO Collection MMO Collection ACE Conclusions ACE Interpretation Describes test for hydrogen Records a positive test for hydrogen Hydrogen/H2 identified from “pop” alone (Solid dissolves in NaOH), white ppt on adding HCl, dissolves (again) in NaOH Allow his mark if precipitate intensifies on adding acid and diminishes on adding NaOH Evidence (from smell) of ester formation. Accept linament, hospital, antiseptic smell but not sweet or fruity Give one mark for concluding that FB 8 is an acid or solution is acidic Give one mark for (aromatic) organic acid or carboxylate/carboxylic functional group Give one mark for any evidence supporting the conclusion of an acid/organic acid – flammable gas from reaction with magnesium, – solubility in NaOH; insolubility in HCl – ester formation (allow from sweet or fruity smell) 1 1 1 1 1 1 1 [7] Qn 2 Total 15