Cambridge A Level Chemistry 9701 — 2013 May/June Paper 3 · Variant 4

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 fl uid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. You may lose marks if you do not show your working or if you do not use appropriate units. Use of a Data Booklet is unnecessary. Qualitative Analysis Notes are printed on pages 12 and 13. 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. CHEMISTRY 9701/34 Advanced Practical Skills 2 May/June 2013 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confi dential Instructions UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certifi cate of Education Advanced Subsidiary Level and Advanced Level This document consists of 12 printed pages and 4 blank pages. [Turn over IB13 06_9701_34/4RP © UCLES 2013 *4504368604* Session Laboratory For Examiner’s Use 1 2 3 Total

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3 9701/34/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use 1 When aqueous hydrochloric acid is mixed with aqueous sodium hydroxide, the neutralisation reaction releases heat causing a rise in the temperature of the solution. HCl (aq) + NaOH(aq) → NaCl (aq) + H2O(l) In this experiment you will mix different volumes of hydrochloric acid and sodium hydroxide but the total volume will be kept constant. For each mixture you will record the temperature rise. Since the combined volume remains the same, the temperature rise is a direct measure of the heat given out by the reaction. The maximum heat given out occurs when all the acid present is exactly neutralised by all the alkali present. By determining the volumes when this occurs you can work out the concentration of the sodium hydroxide. FB 1 is 2.00 mol dm–3 hydrochloric acid, HCl. FB 2 is aqueous sodium hydroxide, NaOH. Read through the instructions carefully and prepare a table for your results in the space on page 4 before starting any practical work. (a) Method Experiment 1 ● Support the plastic cup in the 250 cm3 beaker. ● Fill the unlabelled burette with FB 1. ● Run 26.00 cm3 of FB 1 from the burette into the plastic cup. ● Record the temperature of FB 1, T1, in the space below. T1 = …………. °C ● Fill the burette labelled FB 2 with FB 2. ● Run 4.00 cm3 of FB 2 from the burette into the plastic cup. ● Stir the mixture thoroughly and record in your table the maximum temperature of the solution. ● Empty the plastic cup, rinse thoroughly with water and shake dry. Experiment 2 ● Support the plastic cup in the 250 cm3 beaker. ● Run 22.00 cm3 of FB 1 from the burette into the plastic cup. ● Run 8.00 cm3 of FB 2 from the burette into the plastic cup. ● Stir the mixture thoroughly and record in your table the maximum temperature of the solution. ● Empty the plastic cup, rinse thoroughly with water and shake dry.

4 9701/34/M/J/13 © UCLES 2013 For Examiner’s Use Experiments 3 – 7 ● Repeat the experiment using 18.00, 14.00, 10.00, 6.00 and 2.00 cm3 of FB 1 respectively. Add sufficient FB 2 each time to make sure that the total volume remains 30.00 cm3. For each of your seven experiments, record in the space below ● the volume of FB 1, ● the volume of FB 2, ● the maximum temperature of the solution, ● the temperature rise, ∆T, where ∆T = maximum temperature recorded – T1. [6] (b) (i) On the grid opposite, plot the temperature rise, ∆T, on the y-axis against the volume of FB 1 on the x-axis. The scale for ∆T should extend at least 2 °C above your greatest temperature rise. (ii) Draw a straight line of best fi t through the points where the values of ∆T are increasing. Draw a second straight line of best fi t through the points where the values of ∆T are decreasing. (iii) From your graph, determine the value of the volume of FB 1 where the two lines of best fi t intersect. volume of FB 1 = … cm3 [5] I II III IV V I II III IV V VI

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6 9701/34/M/J/13 © UCLES 2013 For Examiner’s Use (c) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Calculate how many moles of hydrochloric acid are contained in the volume recorded in (b)(iii). moles of HCl = ………………… mol (ii) Calculate how many moles of sodium hydroxide would react completely with the number of moles of hydrochloric acid in (c)(i). moles of NaOH = ………………… mol (iii) Calculate the concentration of FB 2. Remember that the combined volume of FB 1 and FB 2 in each experiment was 30.00 cm3. concentration of FB 2 = …………………….. mol dm–3 [3] (d) A student decided to modify the experiment. The total volume of the solution was increased to 50 cm3 and temperature rises were recorded for 5, 10, 15, 20, 25, 30, 35, 40 and 45 cm3 of FB 2. The volumes were measured using a 50 cm3 measuring cylinder. Discuss how these changes would affect the accuracy with which the concentration of FB 2 could be determined. … … … [2] [Total: 16] I II III

7 9701/34/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use 2 A second way to determine the concentration of an alkali is by volumetric titration. In this experiment you will fi rst dilute the sample of FB 2 that you used in Question 1 and then titrate the diluted solution using hydrochloric acid. HCl (aq) + NaOH(aq) → NaCl (aq) + H2O(l) FB 2 is aqueous sodium hydroxide, NaOH. FB 3 is 0.200 mol dm–3 hydrochloric acid, HCl. (a) Method Dilution of FB 2 ● Use the burette labelled FB 2 to transfer 25.00 cm3 of FB 2 into the 250 cm3 graduated (volumetric) flask, labelled FB 4. ● Make up the contents of the flask to the 250 cm3 mark with distilled water. ● Stopper the flask and mix the contents thoroughly. This solution FB 4. Titration ● Rinse the unlabelled burette thoroughly with distilled water and then with a little FB 3. Fill this burette with FB 3. ● Use a pipette to transfer 25.0 cm3 of FB 4 into a conical flask. ● Add to the flask a few drops of the acid-base indicator provided. ● Titrate the alkali in the flask with the acid, FB 3. You should perform a rough titration. In the space below record your burette readings for this rough titration. The rough titre is …………………… cm3. ● Carry out as many accurate titrations as you think necessary to obtain consistent results. ● Record in a suitable form below all of your burette readings and the volume of FB 3 added in each accurate titration. Make certain that any recorded results show the precision of your practical work. [5] I II III IV V

8 9701/34/M/J/13 © UCLES 2013 For Examiner’s Use (b) From your titration results obtain a suitable value to be used in your calculation. Show clearly how you have obtained this value. 25.0 cm3 of FB 4 required …….…….. cm3 of FB 3. [1] (c) (i) Calculate how many moles of HCl are contained in the volume recorded in (b). moles of HCl = ………………… mol (ii) Hence, calculate how many moles of NaOH are contained in 25.0 cm3 of FB 4. moles of NaOH = ………………… mol (iii) Calculate the concentration of the sodium hydroxide, FB 2. concentration of FB 2 = …………………….. mol dm–3 [3] [Total: 9] I II III

9 9701/34/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use 3 Qualitative Analysis 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 Where gases are released they should be identifi ed 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. No additional tests for ions present should be attempted. If any solution is warmed, a boiling tube MUST be used. Rinse and reuse test-tubes and boiling tubes where possible. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. (a) FB 5, FB 6, FB 7 and FB 8 are aqueous solutions each of which contains a single cation and a single anion. Some of the ions present are listed below. Fe2+ Pb2+ Zn2+ I– OH– SO4 2– By observing the reactions that occur when pairs of the solutions are mixed together, you will be able to identify which solution contains which of these ions.

10 9701/34/M/J/13 © UCLES 2013 For Examiner’s Use ● To a 1 cm depth of FB 6, FB 7 and FB 8 in separate test-tubes add FB 5 dropwise until in excess. Leave each test-tube to stand for a few minutes and note any changes. ● Use a 1 cm depth of each solution for the remaining tests. ● Record your observations in the following table. FB 6 FB 7 FB 8 FB 5 FB 6 FB 7 [6] (b) From your observations deduce which solution contains each of the following ions. ion Fe2+ Pb2+ Zn2+ I– OH– SO4 2– solution [3] I II III IV V VI I II III

11 9701/34/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use (c) FB 9 is an aqueous solution containing either sulfate, SO4 2–, or sulfi te, SO3 2–, ions. Describe how you would determine which ion is present. … … Carry out this test and record your observations and conclusion. observations … … The anion in FB 9 is … . [2] (d) A student is given two different samples and told that each contains one of the following organic compounds. ethanol ethanal ethanoic acid Describe two chemical tests that the student could carry out on each sample to determine which organic compound is present in each sample. For each test, give the reagent(s) to be used and explain how the different observations would allow the identity of the sample to be determined. fi rst reagent … observations … … explanation … … second reagent … observations … … explanation … … [4] [Total: 15] I II III IV

12 9701/34/M/J/13 © UCLES 2013 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, NH4 +(aq) no ppt. 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. turning brown on contact with air insoluble in excess green ppt. turning brown on contact with air 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. rapidly turning brown on contact with air insoluble in excess off-white ppt. rapidly turning brown on contact with air 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.]

13 9701/34/M/J/13 © UCLES 2013 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 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) sulfate, SO4 2–(aq) gives white ppt. with Ba2+(aq) or with Pb2+(aq) (insoluble in excess dilute strong acids) sulfi te, SO3 2–(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, Cl 2 bleaches damp litmus paper hydrogen, H2 “pops” with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidifi ed aqueous potassium dichromate(VI) from orange to green

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CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2013 series 9701 CHEMISTRY 9701/34 Paper 34 (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, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 2013 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

Page 2 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 34 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total 1 (a) PDO layout I Constructs one table for all 7 results. (Table does not need lines, does need something entered for each experiment) 1 PDO recording II Appropriate headings and units for data given. Volume in cm3 or /cm3 or (cm3). Temperature in °C or /ºC or (ºC). (All 4 correct headings and units must appear in the table.) 1 PDO recording III All temperatures recorded to the nearest 0.5 °C both in the table and for T1, at least one of the readings must be .5 (others .0) or vice versa. 1 ACE interpret- ation IV Correctly calculates all 7 temperature rises (from the table(s)). 1 MMO quality V + VI Compare temp rise for addition of 14 cm3 of FB 1 with Supervisor value. Default value = 11.0 °C Award 2 marks for ∆T within ± 1.0 °C. Award 1 mark for ∆T within ± 2.0 °C. 2 [6] (b) (i) PDO layout I ∆T on y-axis and volume of FB 1 on x-axis. Axes clearly labelled (ignore units). 1 II Linear scale chosen to go at least 2 ºC above highest reading and to be a minimum of 6 squares vertically including the 2 ºC; minimum 5 large squares for volume. 1 III All points plotted to within half a small square (6 min). 1 (ii) ACE interpret- ation IV Draws both straight lines of best fit. 1 (iii) V Reads correctly the value of FB 1 from the intercept of the two lines. 1 [5]

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 34 © Cambridge International Examinations 2013 (c) (i) and (ii) ACE interpret- ation I Correctly calculates
.     and same answer for (c)(ii) 1 (iii) II Correctly calculates      .  1 PDO Display III Show use of 2 × (b)(iii)/1000 in (i) and all 3 answers to 3 or 4 sf 1 [3] (d) ACE interpret- ation Any two of: • change in volume makes no difference to the accuracy as temp rise the same • decreased accuracy as less accurate measurement of volume with reference to measuring cylinder or burette (comparative needed or reference to precision/calibration or % error) • more accurate as greater number of experiments so more points to get an accurate intercept or better lines of best fit 2 [2] [Total: 16] 2 (a) MMO collection I Initial and final volumes recorded for rough and initial, final and volume added recorded for accurate titrations. 1 PDO recording II All accurate burette readings recorded to 0.05 cm3. Do not award this mark if: 50(.00) is used as an initial burette reading; more than one final burette reading is 50(.00); any burette reading is greater than 50(.0). 1 MMO decision III Two uncorrected accurate titres within 0.1 cm3. Do not award if, having performed two titres within 0.1 cm3, a further titration is performed that is more than 0.1 cm3 from the closer of the original 2 titres unless a further titration has been carried out which is within 0.1 cm3 of any others. Do not award if titres from burette readings to no dp are used (apart from use of 0 for initial reading). 1

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 34 © Cambridge International Examinations 2013 Examiner rounds any accurate burette readings to the nearest 0.05 cm3, checks subtractions and then selects the ‘best’ titres for Supervisor and candidate using the hierarchy: two identical; titres within 0.05 cm3; titres within 0.1 cm3; etc. to calculate mean correct to 0.01 cm3. Examiner compares candidate mean titre with Supervisor mean titre. (a) (cont.) MMO quality IV + V Award 2 marks if δ ≤ 0.20 cm3. Award 1 mark if 0.20 < δ ≤ 0.50 cm3. If best titres are ≥ 0.50 cm3, cancel one of the Q marks. 2 [5] (b) ACE interpret- ation Check mean titre is correctly calculated from clearly selected values (ticks or working). Candidate must average two (or more) titres that are within 0.20 cm3 of each other. Working must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should normally be quoted to 2 dp rounded to the nearest 0.01. Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for 0.025 or 0.075 eg 26.325; allow mean to 1 dp if all accurate burette readings were given to 1 dp and the mean is exactly correct. eg 26.0 and 26.2 = 26.1 is correct but 26.0 and 26.1 = 26.1 is incorrect. Note: the candidate’s mean will sometimes be marked as correct even if it is different from the mean calculated by the examiner for the purpose of assessing accuracy. 1 [1] (c) ACE interpret- ation I (i) Correctly calculates 0.2 × (b)/1000 and same ans in (ii) to 3 or 4 sf 1 II (c)(ii) × 400 1 PDO display III Working in the correct direction shown in (i) and (iii). 1 [3] [Total: 9]

Page 5 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 34 © Cambridge International Examinations 2013 FB 5 is NaOH(aq); FB 6 is FeSO4(aq); FB 7 is (Zn(NO3)2 + KI)(aq); FB 8 is Pb(NO3)2(aq); FB 9 is Na2SO4(aq) (a) MMO collection I FB 5 and FB 6: a green ppt, insol in excess II turning brown/darkening 1 1 III FB 5 and FB 7: a white ppt, sol in excess 1 If excess omitted in the tests above then allow 1 mark for three correctly coloured ppts. IV FB 5 and FB 8: white ppt, sol in excess 1 V FB 6 and FB 7: no reaction/no change (not dash) (ignore any ref to solution turning yellow/orange/brown) 1 VI FB 6 and FB 8: white ppt and FB 7 and FB 8: yellow ppt 1 [6] (b) ion Fe2+ Pb2+ Zn2+ I– OH– SO4 2– solution FB 6 FB 8 FB 7 FB 7 FB 5 FB 6 (b) ACE con- clusion 6 correct scores 3 marks 5 correct scores 2 marks 3 or 4 correct scores 1 mark (freestanding marks) 3 [3] (c) MMO decision (Aqueous) BaCl2 or Ba(NO3)2 and HCl or HNO3 (or names) or Pb(NO3)2 and HNO3 (either way round but check that obs fit) or add HCl, HNO3, H2SO4 and observe fizzing with SO3 2– or test gas with (acidified) dichromate/ manganate(VII) or add acidified sodium/potassium dichromate/ manganate(VII) (to solution) with SO3 2–: colour change from orange/purple to green/colourless or decolourises 1 MMO collection White ppt insol/no gas/no (further) reaction in acid or no reaction/no gas/no colour change of indicator (from obs) (with Ba2+ route may gain reagent mark if suitable acid is only named in obs) or no colour change of solution/ (from obs) and SO4 2– identified 1 [2]

Page 6 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 34 © Cambridge International Examinations 2013 (d) MMO decision I Choice of first reagent from following list (any) 1 ACE con- clusion II Correct deduction(s) from correct positive obs. 1 MMO decision III Choice of second reagent which is capable of distinguishing between the pair** (e.g. carbonate / dichromate pairing cannot be credited as cannot identify if the two are ethanol and ethanal; ditto Tollens’ and Na) 1 ACE con- clusion IV Correct deduction from correct obs. 1 [4] [Total: 15] ** If both tests identify the same compound, award marks for the higher scoring answer. reagent ethanol ethanal ethanoic acid *acidified potassium (or sodium) dichromate orange/solution turns green orange/solution turns green (no reaction) *acidified potassium manganate(VII) purple/solution turns colourless/pale pink purple/solution turns colourless/pale pink (no reaction) Brady's (2,4– DNP(H)) (no reaction) yellow-orange/ orange/red ppt (no reaction) Tollens’/ammoniacal silver nitrate (no reaction) silver (mirror) grey/black ppt (no reaction) Fehling's (no reaction) orange/red/orange- brown/red-brown ppt (no reaction) Benedict's (no reaction) orange/red/orange- brown/red-brown ppt (no reaction) named carbonate or hydrogen carbonate (no reaction) (no reaction) effervescence/ gas which turns limewater milky magnesium (no reaction) (no reaction) effervescence/ gas which pops with lighted splint

Page 7 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 34 © Cambridge International Examinations 2013 sodium effervescence/ gas which pops with lighted splint (no reaction) effervescence/ gas which pops with lighted splint sodium hydroxide + ref to checking temperature (no reaction) (no reaction) temp increases named indicator (not phenolphthalein) (no reaction) (no reaction) turns correct final colour named alcohol + c. H2SO4 warm/heat (no reaction) (no reaction) sweet/fruity/ester smell named carboxylic acid + c. H2SO4 & warm/heat sweet/fruity/ester smell (no reaction) (no reaction) PCl5 or PCl3/SOCl2 misty/steamy fumes (no reaction) misty/steamy fumes triiodomethane test/ I2+NaOH (pale) yellow ppt (pale) yellow ppt (no reaction) named –oyl chloride sweet/fruity/ester smell (no reaction) (no reaction) * deduction marks allowed from no acidification/H+