Cambridge A Level Chemistry 9701 — 2010 May/June Paper 3 · Variant 1

This document consists of 11 printed pages and 1 blank page. DC (SJF5445/CGW) 11612/5 © UCLES 2010 [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 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 10 and 11. 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 1 4 1 9 1 6 6 8 7 * CHEMISTRY 9701/31 Paper 31 Advanced Practical Skills May/June 2010 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/M/J/10 © UCLES 2010 For Examiner’s Use 1 Read through question 1 before starting any practical work. You are provided with the following reagents. FA 1, 2.0 mol dm–3 sulfuric acid, H2SO4 FA 2, aqueous sodium hydroxide, NaOH The reaction of sulfuric acid with sodium hydroxide is exothermic. In separate experiments you will add increasing volumes of FA 2 to a fixed volume of FA 1. In each experiment you will measure the maximum temperature rise. As the volume of FA 2 is increased, this maximum temperature rise will increase and then decrease. By measuring the maximum temperature rise for different mixtures of the two reagents you are to determine the following. • the concentration of sodium hydroxide, NaOH, in FA 2 • the enthalpy change when 1 mol of H2SO4 is neutralised by NaOH (a) Method • Fill the burette with FA 1. • Support the plastic cup in the 250 cm3 beaker. • Run 10.00 cm3 of FA 1 from the burette into the plastic cup. • Measure 10 cm3 of FA 2 in a measuring cylinder. • Place the thermometer in the FA 2 in the measuring cylinder and record the steady temperature of the solution. • Tip the FA 2 in the measuring cylinder into the plastic cup, stir and record the maximum temperature obtained in the reaction. • Empty and rinse the plastic cup. Rinse the thermometer. Shake dry the plastic cup. • Carry out the experiment four more times. Each time use 10.00 cm3 of FA 1. Use 20 cm3, 30 cm3, 40 cm3 and 50 cm3 of FA 2 in these different experiments. Carry out two further experiments. Choose volumes of FA 2 which will allow you to investigate more precisely the volume of FA 2 that produces the highest temperature rise when added to 10.00 cm3 of FA 1. Results Record your results in an appropriate form showing, for each experiment, the volumes of solution used, temperature measurements and the temperature rise. [9] i ii iii iv v vi vii viii ix

3 9701/31/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (b) Use the grid below to plot a graph of temperature rise (y-axis) against the volume of FA 2 added (x-axis). Draw a line of best fit through the points where the temperature rise is increasing and another line through the points where the temperature rise is decreasing. The intersection of these lines represents the temperature rise for the volume of FA 2 that exactly neutralises the sulfuric acid present in 10.00 cm3 of FA 1. [4] i ii iii iv

4 9701/31/M/J/10 © UCLES 2010 For Examiner’s Use (c) Read from the graph the volume of FA 2 that gives the maximum temperature rise. The volume of FA 2 giving the maximum temperature rise is ………….. cm3. [1] (d) Explain why the temperature rise is plotted on the y-axis rather than on the x-axis. … …[1] (e) Construct the balanced equation for the reaction of sulfuric acid with sodium hydroxide. …[1] (f) (i) Calculate how many moles of sulfuric acid, H2SO4, are contained in 10.00 cm3 of FA 1. 10.00 cm3 of FA 1 contain ………….. mol of H2SO4. (ii) Calculate how many moles of NaOH are required to neutralise the amount of H2SO4 calculated in (i) above. The sulfuric acid in 10.00 cm3 of FA 1 is neutralised by ………… mol of NaOH. [2] (g) Use the equation below to calculate the concentration of NaOH in FA 2. concentration of NaOH (mol dm–3) = answer to (f)(ii) × 1000 volume of FA 2 (cm3) from (c) The concentration of NaOH in FA 2 = ………………………. mol dm–3. [1] (h) Read the maximum temperature rise from the graph and use this to calculate the enthalpy change when 1 mol H2SO4 is neutralised by NaOH. Give your answer in kJ mol–1 and include the correct sign for the reaction. [4.3 J are absorbed or released when the temperature of 1 cm3 of solution changes by 1 °C. Remember that separate volumes of FA 1 and FA 2 were mixed together.] ΔH = ……………………… kJ mol–1. [2]

5 9701/31/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (i) A student suggested that the accuracy of the experiment would be improved if the volume of FA 2 had been measured using a burette rather than a measuring cylinder. Suggest an advantage and a disadvantage of using a burette in the procedure. advantage … … disadvantage … … [2] (j) Identify two further significant sources of error, other than the measurement of volume, in the experiments used for measuring temperature rise. error 1 … … error 2 … … [1] (k) Complete the sections below. (i) The maximum error in taking a temperature reading on a thermometer with graduations at 1 °C is ………………°C. (ii) The temperature rise when 30 cm3 of FA 2 is added to 10.00 cm3 of FA 1 is ………………°C. (iii) Calculate the maximum percentage error due to the thermometer when measuring the temperature rise in (ii) above. The maximum percentage error = ……………… %. [2] [Total: 26]

6 9701/31/M/J/10 © UCLES 2010 For Examiner’s Use 2 Solutions FA 3, FA 4 and FA 5 each contain a Group 2 halide. Solution FA 6 contains a potassium salt. You will carry out tests to deduce the following. • the anion present in FA 6 • the solution containing the chloride ions • the solution containing barium ions At each stage of any test you are to record details of the following. • colour changes seen • the formation of any precipitate and the colour of the precipitate Where gases are released they should be identified 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 directly with a Bunsen burner a boiling-tube MUST be used. Rinse and reuse test-tubes where possible. (a) Use information from the Qualitative Analysis Notes on page 11 to select a pair of reagents that, used together, identify the halide ion present. The reagents are ……………………………..………… followed by ……………………………..………… . [1] (b) Use your chosen reagents to carry out tests on FA 3, FA 4 and FA 5. Record your results in an appropriate form in the space below. [2] (c) From the results of the tests in (b) state which solution contains the chloride ion, Cl –. Solution ………….. contains the chloride ion. Explain the evidence that supports your conclusion. … …[1]

7 9701/31/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (d) Carry out the following tests on each of the solutions FA 3, FA 4 and FA 5. Record your observations below. test observations FA 3 FA 4 FA 5 To 1 cm depth of solution in a test- tube, add 2 cm depth of aqueous sodium hydroxide. To 1 cm depth of solution in a test-tube, add 2 cm depth of aqueous ammonia. To 1 cm depth of solution in a test-tube, add 1 cm depth of FA 6. [3] (e) To 1 cm depth of FA 6 in a test-tube add 1 cm depth of dilute sulfuric acid. observation … …[1]

8 9701/31/M/J/10 © UCLES 2010 For Examiner’s Use (f) From your observations in (d) and (e) you should be able to identify the anion in FA 6 and which of the solutions FA 3, FA 4 or FA 5 contains barium cations. The anion present in FA 6 is ………………………. . Ba2+ ions are contained in solution ………………………. . Explain how your observations support your conclusions for (i) the anion present in FA 6, … … (ii) the solution containing Ba2+ ions. … … [1] Read through the remainder of question 2 before starting further practical work. Heat a half-full 250 cm3 beaker of water for use as a hot water-bath. (g) FA 7, FA 8, FA 9 and FA 10 are organic compounds. Each contains one of the following different functional groups. • primary alcohol • tertiary alcohol • aldehyde • ketone You are to react some of these compounds with some of the following reagents. • acidified aqueous potassium dichromate(VI) • 2,4-dinitrophenylhydrazine (2,4-DNPH) reagent • ammoniacal silver nitrate (Tollens’ reagent) You are provided with the first two reagents. You must prepare the last of these reagents, Tollens’ reagent, immediately before use. Follow the instructions in the box below. To 2 cm depth of aqueous silver nitrate in a boiling-tube add ½ cm depth of aqueous sodium hydroxide. This will produce a brown precipitate of silver(I) oxide. Add aqueous ammonia a little at a time, with continuous shaking, until the brown precipitate just dissolves. Do not add an excess of aqueous ammonia.

9 9701/31/M/J/10 © UCLES 2010 For Examiner’s Use In each of the following tests add a few drops of the reagent to 1 cm depth of FA 7, FA 8, FA 9 and FA 10 in separate test-tubes. In the tests using acidified potassium dichromate(VI) and Tollens’ reagent, if no initial reaction is seen, warm that tube and its contents in your hot water-bath. There is no need to heat any tube to which you have added 2,4-DNPH reagent. Do not heat any tube with a naked flame. Record your results in the table below. Do not carry out tests for the shaded boxes. reagent observations FA 7 FA 8 FA 9 FA 10 acidified potassium dichromate(VI) 2,4-DNPH reagent Tollens’ reagent [3] (h) State which of the solutions contains a tertiary alcohol. Explain the observations leading to your conclusion. FA …………… contains the tertiary alcohol. explanation … … State which of the solutions contains the aldehyde. Explain the observations leading to your conclusion. FA …………… contains the aldehyde. explanation … … [2] [Total: 14]

10 9701/31/M/J/10 © UCLES 2010 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.]

11 9701/31/M/J/10 © UCLES 2010 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); sulfite, 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, Cl2 bleaches damp litmus paper hydrogen, H2 “pops” with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium dichromate(VI) from orange to green

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UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2010 question paper for the guidance of teachers 9701 CHEMISTRY 9701/31 Paper 31 (Advanced Practical Skills), 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 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 2010 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 31 © UCLES 2010 Question 1 Round all thermometer readings to the nearest 0.5°C. Question Sections Indicative material Mark 1 (a) PDO Recording MMO Collection MMO Decisions MMO Quality MMO Quality (i) Presents data in single table of results – to include volume of FA 2, initial and final temperatures and temperature change. (ii) All columns correctly labelled with appropriate unit shown. Must use solidus, brackets or describe unit fully in words. If units not included in column headings every entry must have the correct unit shown. (iii) All thermometer readings recorded to 0.5°C (iv) Follows instructions – uses 10, 20, 30, 40, 50 cm3 of FA 2 + two additional volumes (v) One extra volume of FA 2 on either side of the maximum for the first five expts. or Two extra volumes between identical values for the first five expts. or Two extra volumes the same side as the next highest reading. (vi) and (vii) Check and correct ∆T where necessary. (If multiple readings for max. T then apply hierarchy: take value of consistent readings; take average and correct to nearest 0.5°C) Compare temp rise with that obtained by the Supervisor (Expected value is 14.0°C) For 30 cm3 FA 2: Award (vi) and (vii) for a temp rise of 0.0°, 0.5°, 1.0°C Award (vi) only for a difference of 1.5°C (viii) and (ix) Check and correct ∆T where necessary. Compare temp rise with that obtained by the Supervisor (Expected value is 13.5°C) For 40 cm3 FA 2: Award (viii) and (ix) for a temp rise of 0.0°, 0.5°, 1.0°C Award (viii) only for a difference of 1.5°C 1 1 1 1 1 2 2 [9]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 31 © UCLES 2010 Question Sections Indicative material Mark (b) PDO Layout (i) Temperature (rise) plotted on y-axis against volume (of FA 2) or FA 2 added /cm3 on x-axis. Clearly labelled axes (ignore units unless T, ∆T or V used as labels) (ii) Uniform and sensible scales that allow points to be plotted in at least half of the squares on each axis. (6 × 4 big squares). (0,0) may be considered – as an additional point or with a line going through it (iii) Visual check the “sweep” of all points, for all experiments recorded. Check the plotting of points for 10, 30 and 50 cm3 of FA 2 (and any other “suspect” point) If any point is missing and that experiment was not carried out, check adjacent point Points should be within ½ of a small square, in the correct square Do not award if T plotted instead of ∆T (iv) Appropriate lines drawn through the ascending and descending points. (Ignore any deviation through rounding at the maximum temperature rise) Do not award if both straight lines and curves drawn or there is any forced change in gradient. 1 1 1 1 [4] (c) ACE Interpretation Reads from the graph (to within ½ small square) the volume of FA 2 at the intersection of two lines. Allow rounding to the closest cm3 Do not award this mark if the lines/curves have been rounded at the maximum ∆T. 1 [1] (d) PDO Layout Explains that the temperature rise is the dependent variable or Volume of FA 2 is the independent variable/one that is controlled/one that you vary (or words to that effect) 1 [1] (e) ACE Conclusion Gives correct equation for the reaction (ignore state symbols) 2NaOH + H2SO4 → Na2SO4 + 2H2O or NaOH + H2SO4 → NaHSO4 + H2O 1 [1] (f) PDO Display ACE Interpretation Working is shown in (f)(i) (involves volumes and concentration, 2.0 mol dm–3) and (f)(ii) (any clear mole ratio) Has correct expression for 2.0 1000 10.00 × or an answer of 0.02(00) in (f)(i) and 0.04(00) in (f)(ii) There is no ecf within (f) 1 1 [2] (g) PDO Display Expression given in the question paper is correctly evaluated to 2 or 3 significant figures. Allow a volume, read from rounded curves to be used in this expression. Normal rounding rules apply to the sig fig. 1 [1]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 31 © UCLES 2010 Question Sections Indicative material Mark (h) ACE Interpretation Uses the expression: (answer from (c) + 10) × 4.3 × ∆T read from graph Divides the answer above by answer to (f)(i) and gives answer in kJ mol–1 with –ve sign Do not award this second mark unless candidate has calculated (a volume of soln × 4.3 × ∆T) 1 1 [2] (i) ACE Improvements Advantage of burette: Lower % error or more accurately calibrated (must refer to or infer scale/graduations/markings/divisions) Disadvantage of burette: Takes longer to add the FA 2 1 1 [2] (j) ACE Interpretation Candidate gives two of the following as significant sources of error. Heat loss (to the surroundings) Thermometer graduated at 1°C intervals Drying of cup/thermometer Initial temps of both solutions should be taken Other acceptable sources of error may be seen. 1 [1] (k) ACE Interpretation (i) Maximum error in reading a 1°C graduated thermometer is given as 0.5°C (iii) Calculates answer in 100% in answer 2 in answer × × (k)(ii) (k)(i) 1 1 [2] Total [26]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 31 © UCLES 2010 Question 2 Question Sections Indicative material Mark FA 3 is BaCl2(aq); FA 4 is MgBr2(aq) [MgCl2 + NaBr]; FA 5 is CaI2(aq) [CaCl2 + NaI]; FA 6 is K2CrO4(aq) 2 (a) MMO Decisions Chooses silver nitrate/Ag+(aq)/solution containing Ag+ ions followed by (aqueous) ammonia. 1 [1] (b) PDO Recording MMO Collection Results for three solutions and the two reagents from (a) (or three reagents if (a): ‘Ag++ NH3’, Pb2+) if recorded in a single table (no repetition of solutions or reagents) Give one mark for correct observations with FA 3, FA 4 and FA 5. FA 3 – white ppt with Ag+, soluble in NH3(aq) FA 4 – cream ppt with Ag+, partially soluble or insoluble in NH3(aq) (allow “creamy” not “creamy white”) FA 5 – yellow ppt with Ag+, insoluble in NH3(aq) If Ag+ and Pb2+ in (a), all observations must be correct (ignore any ‘extra’ NH3 if not in (a)) (Pb2+: white, white, yellow ppts respectively) 1 1 [2] (c) ACE Conclusion Mark consequentially on observations in (b) Expected conclusion Identifies FA 3 as solution containing Cl – from “white ppt with Ag+ (soluble in NH3(aq)) given as evidence. Mark consequentially – ecf allowed here. (No retrospective to observations) 1 [1] (d) MMO Collection Mark each of the boxes and see whether correct columns or rows give the better mark. Award the better mark. See table below for the expected observations 1 1 1 [3] FA 3 FA 4 FA 5 + NaOH(aq) ignore white ppt white ppt or “cloudiness” + NH3(aq) no ppt (allow reference to “cloudiness”/”slight white ppt”) white ppt no ppt/no change/ no reaction + FA 6 yellow ppt no ppt/no change/ no reaction/yellow soln no ppt/no change/ no reaction/yellow soln

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9701 31 © UCLES 2010 (e) MMO Collection Records (yellow) solution turning orange (or wtte, e.g. orange solution forms) 1 [1] (f) ACE Conclusions Mark consequentially on observations in (d) and (e) Expected conclusions: Anion in FA 6 is chromate, CrO4 2–, from yellow soln turning orange in (e) or yellow ppt with FA 3 in (d) provided FA 3 not also identified from (d) and FA 3 contains Ba2+ from observations with NaOH and NH3 (or just NaOH if obs with FA 4 and FA 5 are correct with it) or FA 6 in (d) 1 [1] FA 7 is a tertiary alcohol; FA 8 is an aldehyde; FA 9 is a ketone; FA 10 is a primary alcohol (g) MMO Collection One mark for two correct observations with FA 7 One mark for correct observations with FA 8 and FA 9 One mark for two correct observations with FA 10 See table below for expected observations 1 1 1 [3] observations reagent FA 7 FA 8 FA 9 FA 10 acidified dichromate no reaction no reaction (colour change to) green/blue-green/ cyan/turquoise (solution not ppt) 2,4-DNPH no reaction yellow ppt yellow ppt Tollens’ reagent no reaction silver mirror or black/grey solution or ppt no reaction (h) ACE Conclusions No ecf from (g) FA 7 contains the tertiary alcohol from no reaction with all three reagents or no reaction with dichromate and 2,4-DNPH provided there is no CON in the observation with Tollens’ FA 8 contains the aldehyde from the silver (mirror), black or grey precipitate or solution with ammoniacal silver nitrate Allow from brown ppt if it is the only positive result with Tollens’. 1 1 [2] Total [14]