Cambridge A Level Chemistry 9701 — 2011 May/June Paper 3 · Variant 1

This document consists of 11 printed pages and 1 blank page. DC (SM) 33746/4 © UCLES 2011 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level * 4 4 5 6 0 4 8 6 0 4 * CHEMISTRY 9701/31 Advanced Practical Skills May/June 2011 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Instructions to Supervisors 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. For Examiner’s Use 1 2 3 Total Session Laboratory

2 9701/31/M/J/11 © UCLES 2011 For Examiner’s Use 1 FA 1 is sulfuric acid, H2SO4, of approximate concentration 0.7 mol dm–3. FA 2 is 0.150 mol dm–3 sodium hydroxide. You are also provided with phenolphthalein (indicator). You will determine the exact concentration of FA 1 by titration. H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l) (a) Method Dilution • Pipette 25.0 cm3 of FA 1 into the 250 cm3 graduated (volumetric) flask labelled FA 3. • Make the solution up to the mark using distilled water. • Shake the flask to mix the solution of FA 3. Titration • Rinse out the pipette with distilled water and then with FA 3. • Pipette 25.0 cm3 of FA 3 into a conical flask. • Add 5 drops of phenolphthalein indicator to the flask. The indicator should remain colourless. • Fill the burette with FA 2. • Titrate FA 3 with FA 2, until a permanent pale pink colour is obtained. 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 FA 2 added in each accurate titration. • Make sure that your recorded results show the precision of your practical work. [7] (b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. 25.0 cm3 of FA 3 required … cm3 of FA 2. [1] I II III IV V VI VII

3 9701/31/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use (c) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate how many moles of NaOH were present in the volume of FA 2 calculated in (b). … mol of NaOH (ii) Calculate how many moles of H2SO4 were present in 25.0 cm3 of FA 3. H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l) … mol of H2SO4 (iii) Calculate how many moles of H2SO4 were present in 25.0 cm3 of the undiluted solution FA 1. … mol of H2SO4 (iv) Calculate the concentration, in mol dm–3, of H2SO4 in FA 1. The concentration of H2SO4 in FA 1 was … mol dm–3. [4] [Total: 12] I II III IV

4 9701/31/M/J/11 © UCLES 2011 For Examiner’s Use 2 You will determine, using Hess’ Law, the enthalpy change, ΔH1, for the reaction of magnesium with oxygen to form magnesium oxide. Mg(s) + ½O2(g) MgO(s) (a) Reaction of magnesium with sulfuric acid Method FA 4 is 0.64 mol dm–3 sulfuric acid. FA 5 is magnesium turnings. This is supplied in two containers. You will carry out the experiment twice. • Support the plastic cup in a 250 cm3 beaker. • Using a measuring cylinder, transfer 25 cm3 of FA 4 into the plastic cup. • Tilt the beaker so that the bulb of the thermometer is covered by the solution. Measure and record the initial temperature of the solution. • Carefully, add all the FA 5 from one of the containers into the plastic cup. • Stir the mixture constantly with the thermometer. • Record the highest temperature obtained. • Empty and rinse the plastic cup and dry it with a paper towel. • Repeat the experiment using the second portion of FA 5. In the space below, record all your readings in an appropriate form. Calculate the mean temperature rise. mean temperature rise = … °C [5] Calculation Show your working and express your answers to three significant figures. (i) Using the mean temperature rise above, calculate the mean heat energy produced in the reaction. (You may assume that 4.3 J are required to raise the temperature of 1.0 cm3 of any solution by 1.0 °C.) heat energy produced = … … value unit I II III IV V

5 9701/31/M/J/11 © UCLES 2011 [Turn over For Examiner’s Use (ii) Calculate the enthalpy change, ΔH2, in kJ mol–1, for the following reaction. Mg(s) + H2SO4(aq) MgSO4(aq) + H2(g) You should assume that the magnesium in your reaction is in excess. ΔH2 = … … kJ mol–1 [2] sign value (b) Reaction of magnesium oxide with sulfuric acid Method FA 4 is 0.64 mol dm–3 sulfuric acid. FA 6 is magnesium oxide. • Using a measuring cylinder, transfer 50 cm3 of FA 4 into a 250 cm3 beaker. • Place the beaker on a tripod and gauze, and heat gently until the temperature of the acid reaches 45 °C–60 °C. • Support a plastic cup in a 250 cm3 beaker. • Transfer all the solution of hot FA 4 into the plastic cup. • Stir and record the temperature of hot FA 4. • Immediately add all the FA 6 to the FA 4 in the plastic cup. • Stir the mixture constantly with the thermometer. • Record the highest temperature obtained. In the space below, record all your readings in an appropriate form. [3]

6 9701/31/M/J/11 © UCLES 2011 For Examiner’s Use Calculation Show your working and express your answers to three significant figures. (i) Calculate the heat energy produced in the reaction. (You may assume that 4.3 J are required to raise the temperature of 1.0 cm3 of any solution by 1.0 °C.) heat energy produced = … … value unit (ii) Calculate the enthalpy change, ΔH3, in kJ mol–1, for the following reaction. MgO(s) + H2SO4(aq) MgSO4(aq) + H2O(l) You should assume that the magnesium oxide in your reaction is in excess. ΔH3 = … … kJ mol–1 sign value (iii) The enthalpy change for the following reaction is –286 kJ mol–1. H2(g) + ½O2(g) H2O(l) ΔH = –286 kJ mol–1 Use the Hess’ Law cycle given below to calculate ΔH1, the enthalpy change for the reaction of magnesium with oxygen. ΔH1 Mg(s) + H2SO4(aq) + ½O2(g) MgO(s) + H2SO4(aq) ΔH2 ΔH3 –286 kJ mol–1 MgSO4(aq) + H2(g) + ½O2(g) MgSO4(aq) + H2O(l) ΔH1 = … … kJ mol–1 [3] sign value (c) Suggest one improvement to the method by which heat losses from your apparatus could have been reduced. … …[1] [Total: 14]

7 9701/31/M/J/11 © UCLES 2011 [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 When 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 should be attempted. If any solution is warmed, a boiling tube MUST be used. Rinse and re-use test-tubes and boiling tubes where possible. Where reagents are selected for use in a test, the full name or correct formula of the reagents must be given. (a) FA 7 contains one cation and one anion from those listed in the Qualitative Analysis Notes on pages 10 and 11. Put two spatula measures of FA 7 into a test-tube. Add about two-thirds of a test-tube of distilled water and dissolve the solid. For each test that you carry out, use 1 cm depth of the solution of FA 7. (i) Carry out the following tests and complete the table below. test observation(s) Add 5 drops of aqueous barium chloride (or barium nitrate) to your solution of FA 7. Add 5 drops of aqueous silver nitrate to your solution of FA 7. I II III

8 9701/31/M/J/11 © UCLES 2011 For Examiner’s Use (ii) Put a very small spatula measure of solid FA 7 into a hard glass test-tube. Hold the test-tube horizontally and heat it gently for a few seconds, then heat it strongly until no further change takes place. Leave the test-tube to cool to room temperature. While cooling takes place, move on to (iv). In the space below record the observations made at each stage in an appropriate form. (iii) State what deductions you can make about the identity of the anion in FA 7 from the tests above. … … (iv) Use the information in the Qualitative Analysis Notes on pages 10 and 11 to select a further test to confirm the identity of the anion in FA 7. test … Carry out this test and, in the space below, record the observation(s) made in an appropriate form. State your conclusion. (v) The cation in FA 7 is aluminium ion, calcium ion or zinc ion. Select one reagent to identify the cation in FA 7. reagent … Use this reagent to carry out a test. Record the observation(s) made and identify the cation. … … … …[9] IV V VI VII VIII IX

9 9701/31/M/J/11 © UCLES 2011 For Examiner’s Use (b) FA 8 contains one cation from those listed on page 10 and 11. Put all of the FA 8 into a test-tube. Half fill the test-tube with distilled water and dissolve the solid. (i) To 1 cm depth of the solution of FA 8 in a test-tube, add aqueous potassium iodide until the test-tube is half full. Allow the mixture to stand for two minutes. Use a dropping pipette to transfer about 1 cm3 of the mixture from the top of the test-tube to another test-tube. Add 5 drops of starch solution. Record all of your observations. (ii) State what type of chemical behaviour has been shown by potassium iodide in this reaction. Give an ionic equation to justify your answer. … … … (iii) To another 1 cm depth of solution of FA 8 in a test-tube, add aqueous sodium hydroxide. Record the observation(s) made. Give the ionic equation for the reaction taking place. … … … …[5] [Total: 14] I II III IV V

10 9701/31/M/J/11 © UCLES 2011 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.]

11 9701/31/M/J/11 © UCLES 2011 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

12 9701/31/M/J/11 © UCLES 2011 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. BLANK PAGE

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2011 question paper for the guidance of teachers 9701 CHEMISTRY 9701/31 Paper 31 (Advanced Practical Skills 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, 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. • Cambridge will not enter into discussions or correspondence in connection with these mark schemes. Cambridge is publishing the mark schemes for the May/June 2011 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 2011 9701 31 © University of Cambridge International Examinations 2011 Question Sections Indicative material Mark 1 (a) PDO Layout I Volume given for rough titre and accurate titre details tabulated. Minimum of 2 × 2 boxes. 1 MMO Collection II Initial and final burette readings recorded for rough titre and initial and final burette readings and volume of FA 2 added recorded for each accurate titre. Headings should match readings. 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.(00) 1 PDO Recording III All accurate burette readings (initial and final) recorded to nearest 0.05 (cm3) Assessed on burette readings only. 1 IV Has two uncorrected, accurate titres within 0.1 cm3 Do not award this mark if having performed two titres within 0.1 cm3 a further titration is performed which is more than 0.10 cm3 from the closer of the initial two titres, unless a fourth titration, within 0.1 cm3 of any of the previous titres has also been carried out. 1 Round any burette readings to the nearest 0.05 cm3. Check and correct subtractions in the titre table. Examiner then selects the “best” titre using the hierarchy: two identical; titres within 0.05 cm3; titres within 0.1 cm3; etc MMO Quality V, VI and VII Award V, VI and VII for a difference from Supervisor within 0.20 cm3 Award V and VI for a difference of > 0.20 – ≤ 0.40 cm3 Award V for a difference of > 0.40 – ≤ 0.60 cm3 If the “best” titres are ≥ 0.60 cm3 apart cancel one of the Q marks. 3 [7]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 31 © University of Cambridge International Examinations 2011 (b) ACE Interpretation Calculates the mean, correct to 2 decimal places from any accurate titres within 0.20 cm3. The third decimal place may be rounded to the nearest 0.05 cm3. A mean of exactly .x25 or .x75 is allowed but the candidate may round up or down to the nearest 0.05 cm3. If ALL burette readings are given to 1 decimal place then the mean can be given to 1 decimal place if numerically correct without rounding. Mean of 24.3 and 24.4 = 24.35 (✓) Mean of 24.3 and 24.4 = 24.4 () Titres to be used in calculating the mean must be clearly shown – in an expression or ticked in the titration table. 1 [1] (c) ACE Interpretation I Expression needed in step (i) (= mean titre x 0.15/1000 mol) and step (ii) (= answer to step (i) / 2) No irrelevant or incorrect working should be included. 1 II Correctly evaluates step (iii) (= answer to step (ii) × 10) and step (iv) (= answer to step (iii) × 40) 1 PDO Display III Some relevant working shown in a minimum of three parts in the calculation. (In (ii) could be × 2 or ÷ 2, in (iii) could × 10 or ÷ 10). 1 IV All answers given are quoted to 3 or 4 sig figs (must be a minimum of three steps) 1 [4] [Total: 12]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 31 © University of Cambridge International Examinations 2011 2 (a) MMO Collection I Two pairs of temperature values recorded as instructed in (a), with units for all readings in (a) and (b) – minimum of 3 readings. Acceptable units are /ºC, (ºC), temperature in degrees Celsius, temperature in ºC. 1 PDO Recording II All thermometer readings recorded to 0.0 oC or 0.5 oC. (check readings in sections 2(a) and 2(b) – minimum of 4 readings). 1 ACE Interpretation III Correct subtractions to give temperature rises and the correct mean value in 2(a). Mean value may be rounded to 0.5 oC or to one d.p or to 0.05 oC and from 0.025 and 0.075 or these may be rounded up or down to nearest 0.1. 1 Supervisor script: check subtractions and calculate mean ∆T Marks are awarded for comparing the “true” means: check working of candidate and Supervisor. Show Supervisor’s mean (corrected if necessary) on the script in a ring. MMO Quality Award IV and V if candidate’s mean temp rise is within 2.0 oC of Supervisor’s (incl) Award IV if the difference is between 2.0 oC and 3.0 oC. 1 1 [5] PDO Display Heat produced (J) = 25 × 4.3 × temp rise (method mark). Unit is needed in the quoted answer (kJ if divided by 1000). Correctly evaluates enthalpy change = heat produced/ 0.016. Division by 1000 is not required if candidate did this in the previous step. Answer must be negative and to 3 sig figs. 1 1 [2]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 31 © University of Cambridge International Examinations 2011 Examiner to calculate 20% and 40% of supervisor’s ∆T and convert to nearest 0.5oC. (b) ACE Interpretation MMO Quality I Both temperature measurements clearly shown. Award II and III if candidate’s temp rise is within 20% of Supervisor’s. Award II if candidate’s temp rise is within 40% of Supervisor’s. 1 1 1 [3] ACE Interpretation PDO Display ACE Conclusions IV Calculates 0.032 for moles in (ii) or 0.016 for moles in (a)(ii). V Enthalpy change correctly calculated (= – heat change/0.032). Answer must show negative sign (unless already penalised) and be given to 3 sig figs. (unless already penalised). VI Correct calculation of enthalpy change ∆H1 = ∆H2 – ∆H3 – 286 1 1 1 [3] (c) ACE Improvements Extra/thicker lagging or use a lid or use a vacuum flask 1 [1] [Total: 14]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2011 9701 31 © University of Cambridge International Examinations 2011 FA 7 is Zn(NO3)2(s); FA 8 is CuSO4(s) 3 (a) (i) (ii) (iii) (iv) (v) MMO Collection MMO Collection ACE Conclusions MMO Decisions MMO Collection MMO Decisions ACE Conclusions No change (or no precipitate or no reaction) both with barium chloride and silver nitrate. Gentle heat: solid melts or dissolves or gives a colourless liquid Brown fumes/gas produced (allow ‘qualified’ brown e.g. red/brown, do not allow orange). (Gas produced) that relights a glowing splint or yellow solid, goes white on cooling. (Allow precipitate). FA 7 is a nitrate/nitrite (from some evidence) (Heat) FA 7 with Al foil and NaOH/ecf from anion given. Gas/vapour/NH3 produced and it turns red litmus to blue and confirms that FA 7 contains nitrate/nitrite ions. Adds ammonia. (This mark is not awarded if a second test is also used) Zinc ions are present. (No ecf) (Deduction must be consistent with observations recorded – white ppt soluble in excess). 1 1 1 1 1 1 1 1 1 [9] (b) (i) (ii) (iii) MMO Collection ACE Conclusions MMO Collection ACE Conclusions With KI, goes yellow/orange/brown and gives a blue (blue-black or purple or black) colour with starch. No reference to the state is required, just the colours. Brown/yellow/white/off- white precipitate forms. KI is the reducing agent (or it is oxidised) as iodine is formed or 2I– – 2e–
I2 or 2Cu2+ + 2I–
I 2 + 2Cu+ Ignore state symbols. Blue (do not allow dark blue) precipitate obtained, which does not dissolve in excess NaOH Cu2+ + 2OH–
Cu(OH)2 1 1 1 1 1 [5] [Total: 14]