Cambridge A Level Chemistry 9701 — 2007 Oct/Nov Paper 3 · Variant 1

This document consists of 12 printed pages and 1 Insert. SP (SM/KS) T47239/2 © 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. * 3 3 1 8 2 3 0 6 2 8 * CHEMISTRY 9701/31 Paper 31 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 9701/31/O/N/07 © UCLES 2007 1 Read through question 1 before starting any practical work. You are provided with the following reagents. FA 1 containing 37.0 g dm–3 of hydrated sodium thiosulphate, Na2S2O3.5H2O FA 2 2.0 mol dm–3 hydrochloric acid, HCl distilled water Aqueous thiosulphate ions, S2O3 2–, decompose in the presence of hydrogen ions, H+. S2O3 2–(aq) + 2H+(aq) → S(s) + SO2(g) + H2O(l) The rate of reaction can be followed by observing the formation of a fixed amount of sulphur as a fine suspension of solid particles in the solution. The rate of decomposition at a fixed temperature is affected by • the concentration of thiosulphate ions, [S2O3 2–]; • the concentration of hydrogen ions, [H+]. 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 thiosulphate ions can be obtained by plotting a graph of log rate against log [S2O3 2–]. order of reaction = gradient of straight line log [S2O3 2–] log rate For Examiner’s Use

3 9701/31/O/N/07 [Turn over © UCLES 2007 (a) Method Experiment 1 • Fill the burette labelled FA 1 with FA 1. • Run 50.00 cm3 of FA 1 from the burette into a 250 cm3 beaker. • Measure 5 cm3 of FA 2 in a measuring cylinder. • Tip the acid FA 2 from the measuring cylinder into the beaker and immediately start a stop-clock or note the start time on a clock with a second hand. • Swirl the beaker to mix the reagents and place the beaker over the printing on the insert provided. • Observe the printing by looking down through the solution in the beaker. • Stop the clock or note the time when the printing is just no longer visible. • Record the time taken to the nearest second. The time taken is … s. Experiment 2 • Empty and rinse the beaker used in experiment 1. Carefully dry the beaker with a paper towel. • Refill the burette labelled FA 1 with FA 1. • Fill the second burette, labelled water, with distilled water. • Run 10.00 cm3 of FA 1 and 40.00 cm3 of distilled water from the burettes into the 250 cm3 beaker. • Measure 5 cm3 of FA 2 in a measuring cylinder. • Tip the acid FA 2 into the beaker, start the clock or note the time, mix the reagents and place over the printing as in experiment 1. • Stop the clock or note the time when the printing is just no longer visible. • Record the time taken to the nearest second. The time taken is … s. [2] For Examiner’s Use

4 9701/31/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 thiosulphate ions is varied. In selecting the mixtures to be used you should consider • how many mixtures need to be used, • what concentrations of thiosulphate ion should be used, • what range these concentrations should cover, • that only the concentration of thiosulphate ion must change. Remember – you already have reaction times for two mixtures with different concentrations of thiosulphate ion. 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 FA 1). Carry out the additional experiments and record your results. [11] i ii iii iv v vi vii viii ix x xi

5 9701/31/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 FA 1). Draw an appropriate straight line through the points plotted. [4]

6 9701/31/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 thiosulphate ions. The reaction is … order with respect to thiosulphate ions, S2O3 2–. [3] (e) The moment at which the printing is just obscured can be difficult to judge and will vary from person to person. Explain why this uncertainty for experiment 1 in section (a) will be less than the uncertainty for experiment 2 in section (a). … … … Estimate a value (± seconds) for the uncertainty in each of experiments 1 and 2 and express this uncertainty as a percentage of the time for the reaction. experiment 1 experiment 2 reaction time / s uncertainty / s ± ± percentage uncertainty [3]

7 9701/31/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 hydrogen ions, H+, to be investigated. You will perform two further experiments using the method for experiment 2 in section (a). You will keep the concentration of thiosulphate ions constant and vary the concentration of hydrogen ions. First copy the reaction time from your results to experiment 2 in section (a) into the table below. Then complete the table below to show the volumes of FA 1, FA 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 of FA 1 / cm3 volume of FA 2 / cm3 volume water / cm3 reaction time / s experiment 2 in section (a) 10.00 5 40.00 experiment i experiment ii [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 hydrogen ions. … … … … …[1] [Total: 25]

8 9701/31/O/N/07 For Examiner’s Use © UCLES 2007 2 The four solutions FA 3, FA 4, FA 5 and FA 6 each contain one of the following anions. nitrate, NO3 – nitrite, NO2 – sulphate, SO4 2– sulphite, SO3 2– (a) Use information from the Qualitative Analysis Notes on page 12 to answer the following questions. What single reagent could you use to identify the solution containing the nitrite ion? … What reagents could you use to identify the sulphate and sulphite ions? … and … [1] (b) Use the reagents selected in (a) to test each of the four solutions. Record in the space below, the reagents used and the observations made. From your observations identify the solutions containing nitrite, sulphate and sulphite ions. Solution … contains the nitrite ion. supporting evidence … Solution … contains the sulphate ion. supporting evidence … Solution … contains the sulphite ion. supporting evidence … [7]

9 9701/31/O/N/07 [Turn over For Examiner’s Use © UCLES 2007 (c) You are to perform the tests given in the table below with each of the solutions FA 3, FA 4, FA 5 and FA 6 to identify three of the cations present. One of these cations is the Ba2+ ion. 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 the 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 FA 3 FA 4 FA 5 FA 6 (i) To 1 cm depth of solution in a boiling-tube, add aqueous sodium hydroxide a little at a time until there is no further change. If no precipitate forms, carefully warm the solution. CARE - heated solutions containing sodium hydroxide can be ejected from the boiling-tube. (ii) To 1 cm depth of solution in a test-tube, add aqueous ammonia a little at a time until there is no further change. (iii) To 1 cm depth of solution in a test-tube add 1 cm depth of dilute sulphuric acid. (iv) To 1 cm depth of solution in a test-tube add 1 cm depth of aqueous sodium sulphite. If a precipitate forms, add 2 cm depth of dilute hydrochloric acid. [3]

10 9701/31/O/N/07 For Examiner’s Use © UCLES 2007 (d) From your observations in (c) you should be able to identify the cation present in three of the solutions. Solution … contains the … ion. supporting evidence … … Solution … contains the … ion. supporting evidence … … Solution … contains the … ion. supporting evidence … … [3] (e) Do not carry out this test. What other reagent could you use to confirm the presence of Ba2+ in one of the solutions? …[1] [Total: 15]

11 9701/31/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 9701/31/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 9701/31 Paper 31 (Practical 1), maximum raw mark 40 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. 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 31 © 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 31 © 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 expts. 1 & 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 MMO Decisions (i) Single table for all experiments performed. (Expts 1&2 must be included; minimum for table is volume and time for expts 1&2) A single table has no repetition of headings. (ii) Table has been drawn up in advance. (must have minimum of 4 expts tabulated – does not have to include expts 1&2) – volumes of FA 1 are sequential. Expts 1 and 2 may be entered first or last. (iii) Table includes columns for volume of FA 1 or log(volume of FA 1), time, 1/t or log(1/t). Ignore other columns or if total volume in expt ≠ 55 (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 (vi) At least 3 mixtures – in addition to expt 1 and expt 2. (vii) Volumes of FA 1 chosen are uniformly spaced over the whole range 1 1 1 1 1 1 1

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 31 © UCLES 2007 Question Sections Indicative material Mark Accuracy Calculate (vol of FA 1 x time) for expt 1 and the two additional expts with greatest volume of FA 1. (Round all times to the nearest second) Record the Vt values against the appropriate expt on the candidate’s script. 1 (b) contd. MMO Decisions (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 expt 1 is within 10% of that obtained by the Supervisor. [Award point (xi) but not point (x) for a difference of 10+% to 20%] 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 FA 1 or (log volume of FA 1)) 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 A point must be plotted for each experiment performed – take care where expts 1&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 1 1 1

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 31 © UCLES 2007 Question Sections Indicative material Mark 1 (c) contd 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 [4] If a candidate has only performed experiments 1&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 31 © UCLES 2007 Question Sections Indicative material Mark 1 (e) ACE Interpretation Explains that uncertainty is less when change is rapid (or converse) Estimated errors expt 1 number of seconds ≤ 3 s. expt 2 number of seconds ≥ 3 s, up to a maximum of 10 s. error for expt 2 > error for expt 1 Candidate’s uncertainties correctly expressed as % of reaction time. Error may be carried forward. 1 1 1 [3] 1 (f) ACE Improvements Has: constant volumes of FA 1, variable volume of FA 2, water to keep total volume constant at 55 cm3 Record the total volume 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 acid concentration. [Do not give this mark where mixtures selected in (f) are not appropriate] Little change in reaction time is expected. The rate increases slightly as the concentration of acid is doubled etc. 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 31 © UCLES 2007 Question Sections Indicative material Mark FA 3 is aqueous ammonium sulphite (ammonium chloride + sodium sulphite), FA 4 is aqueous sodium nitrite, FA 5 is aqueous barium nitrate, FA 6 is aqueous manganese(II) sulphate, 2 (a) MMO Decisions Chooses named dilute acid as single reagent for identifying nitrite and chooses BaCl2/ Ba(NO3)2 (Ba2+(aq) or aqueous solution containing Ba2+ acceptable) together with HCl/HNO3 (not H2SO4) as reagents for identifying sulphate/sulphite 1 [1] 2 (b) MMO Collection Award the C3 marks only from observations in the table. No retrospective marks. Give one mark for a brown gas evolved from FA 4 with any acid Give one mark for one of the following for FA 6: 1. a white ppt with Ba2+ insoluble in hydrochloric or nitric acid, 2. a white ppt with Ba2+ insoluble in unnamed acid, 3. precipitate whose colour has not been described insoluble in named acid other than H2SO4 Give one mark for one of the following for FA 3: 1. a white ppt with Ba2+ soluble in hydrochloric or nitric acid, 2. a white ppt with Ba2+ soluble in unnamed acid, 3. precipitate whose colour has not been described soluble in named acid other than H2SO4 If sulphuric acid is stated in the table in (b) award one observation mark only, if the barium salt is added before the acid and a white ppt is obtained with FA 6 and with FA3. OR Give one mark for adding HCl/HNO3 and detecting SO2 (dichromate turning green) from FA 3 Give one mark for adding Ba2+(aq) and observing a white ppt with FA 6 and no ppt with FA 3. Do not give the first of these marks if dichromate is added to the acidified mixture (additional reagent) but allow conclusions from that test) 1 1 1 (1) (1)

Page 8 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2007 9701 31 © UCLES 2007 Question Sections Indicative material Mark 2 (b) contd ACE Conclusions ACE Interpretation Give one mark each if the ions are correctly identified (No evidence is required in this section for the identification of the ions) Mark conclusions consequentially to observations FA 4 – nitrite FA 6 – sulphate FA 3 – sulphite Gives appropriate evidence for identification of two of the ions. This mark can be awarded for correct anions where no observations are tabulated. 1 1 1 1 [7] 2 (c) MMO Collection FA 6 – observes off-white ppt insoluble in excess with both NaOH and NH3(aq) FA 5 – observes white ppt in (iii) and white ppt soluble in HCl in (iv) Ignore any ppt with NaOH/NH3. FA 3 – positive test for alkaline gas described with FA 3 only. 1 1 1 [3] 2 (d) ACE Conclusions ACE Interpretation Give two marks if all ions are correctly identified. FA 6 – Mn2+ (from off-white ppt with NaOH and NH3(aq) or off white ppt with NaOH or NH3(aq) soluble in excess) FA 5 – Ba2+ (if observation mark given in (c) or white ppt with H2SO4 and no ppt with NH3(aq)) FA 3 – NH4 + (from ammonia/alkaline gas on warming with NaOH) Give one of these two marks for 2 correct ions Mark conclusions consequentially to observations, e.g. Fe3+ from brown ppt for FA 6. Do not allow Ca2+ or Mg2+ in place of Ba2+. Gives appropriate evidence (minimum – as above) for identification of two of the ions. Evidence for Ca2+ (from reaction with OH–) may be allowed here 1 1 1 [3] If a candidate does not record any practical work for sections (iii) and (iv), ions such as Ca2+, Mg2+or Zn2+ may be credited from appropriate observations with NaOH and NH3(aq) 2 (e) MMO Decisions Selects CrO4 2– or Cr2O7 2– as additional reagent (No cation or “aqueous ion” required) 1 [1] Qn 2 Total 15