Cambridge A Level Chemistry 9701 — 2012 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. 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. CHEMISTRY 9701/34 Advanced Practical Skills 2 May/June 2012 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 11 printed pages and 1 blank page. [Turn over IB12 06_9701_34/4RP © UCLES 2012 *3597482834* Session Laboratory For Examiner’s Use 1 2 Total

2 9701/34/M/J/12 © UCLES 2012 For Examiner’s Use 1 You are to determine the percentage by mass of sodium ethanedioate in a mixture of sodium ethanedioate and ethanedioic acid. This experiment involves two steps. In step one, you will carry out a titration to fi nd the amount of acid, C2O4H2, present in FB 3. In step two, you will carry out a second titration to fi nd the total amount of ethanedioate ion, C2O4 2–, present in FB 3. Finally, you will use the values found in the two steps to calculate the percentage by mass of sodium ethanedioate in FB 3. FB 1 is 0.100 mol dm–3 sodium hydroxide, NaOH. FB 2 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4. FB 3 is a mixture of aqueous sodium ethanedioate, C2O4Na2, and ethanedioic acid, C2O4H2. FB 4 is approximately 2 mol dm–3 sulfuric acid. phenolphthalein indicator Read through the whole method before starting any practical work. (a) Method Step 1 ● Fill the burette labelled FB 1 with FB 1. ● Pipette 25.0 cm3 of FB 3 into a conical flask. ● Add about three drops of phenolphthalein. ● Perform a rough titration and record your burette readings in the space below. The rough titre is … cm3. ● Carry out as many accurate titrations as you think necessary to obtain consistent results. ● Make certain any recorded results show the precision of your practical work. ● Record in a suitable form below all of your burette readings and the volume of FB 1 added in each accurate titration.

3 9701/34/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use I II III IV V VI VII VIII IX X XI XII Step 2 ● Pipette 25.0 cm3 of FB 3 into a conical flask. ● Using a measuring cylinder, add about 25 cm3 of 2 mol dm–3 sulfuric acid, FB 4, to the flask. ● Place the conical flask on a tripod and gauze and heat to about 80 °C. ● Fill the burette labelled FB 2 with FB 2. ● Use an appropriate method to carefully transfer the hot conical flask onto a white tile under the burette. ● Titrate the mixture in the conical flask with FB 2 until a permanent pale pink colour is seen. If a permanent brown colour is seen, stop the titration and begin Step 2 again. ● Perform a rough titration and record your burette readings in the space below. The rough titre is … cm3. ● Carry out as many accurate titrations as you think necessary to obtain consistent results. ● Make certain any recorded results show the precision of your practical work. ● Record in a suitable form below all of your burette readings and the volume of FB 2 added in each accurate titration. [12] Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (b) (i) From your accurate titration results in Step 1, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. 25.0 cm3 of FB 3 required ………….. cm3 of FB 1.

4 9701/34/M/J/12 © UCLES 2012 For Examiner’s Use (ii) Write an equation for the reaction between sodium hydroxide and ethanedioic acid to give sodium ethanedioate and water. … (iii) Use your answer from (i) to calculate the number of moles of sodium hydroxide, FB 1, required to react with 25.0 cm3 of FB 3 in Step 1. moles of NaOH = ………………….. mol (iv) Use your answer to (iii) to determine the number of moles of ethanedioic acid in 25.0 cm3 of FB 3. moles of C2O4H2 in 25.0 cm3 of FB 3 = ………….. mol [2] (c) (i) From your accurate titration results in Step 2, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. 25.0 cm3 of FB 3 required ………….. cm3 of FB 2. (ii) Use your answer from (i) to calculate the number of moles of potassium manganate(VII), FB 2, required to react with 25.0 cm3 of FB 3 in Step 2. moles of KMnO4 = … mol (iii) The equation for the reaction between acidifi ed manganate(VII) ions and ethanedioate ions is shown below. 2MnO4 –(aq) + 5C2O4 2–(aq) + 16H+(aq) → 2Mn2+(aq) + 10CO2(g) + 8H2O(l) Calculate the total number of moles of ethanedioate ions in 25.0 cm3 of FB 3. total moles of C2O4 2– in 25.0 cm3 of FB 3 = ………….. mol

5 9701/34/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use (iv) Use your answers to (b)(iv) and (c)(iii) to calculate the number of moles of ethanedioate ions which came from the sodium ethanedioate dissolved in 25.0 cm3 of FB 3. moles of C2O4 2– from C2O4Na2 in 25.0 cm3 of FB 3 = …………….. mol [4] (d) (i) Use your answer to (b)(iv) to calculate the mass of ethanedioic acid, C2O4H2, in 25.0 cm3 of FB 3. [Ar: H, 1.0; C, 12.0; O, 16.0] (If you were unable to answer (b)(iv), you may assume that the number of moles of ethanedioic acid is 6.51 × 10–4 mol.) mass of ethanedioic acid = … g (ii) Use your answer to (c)(iv) to calculate the mass of sodium ethanedioate, C2O4Na2 in 25.0 cm3 of FB 3. [Ar: C, 12.0; O, 16.0; Na, 23.0] (If you were unable to answer (c)(iv), you may assume that the number of moles of sodium ethanedioate is 4.13 × 10–4 mol.) mass of sodium ethanedioate = … g (iii) Calculate the percentage by mass of sodium ethanedioate present in FB 3. Percentage by mass of sodium ethanedioate present is … %. [4] I II III IV I II III IV

6 9701/34/M/J/12 © UCLES 2012 For Examiner’s Use (e) (i) What is the maximum error in a single burette reading? maximum error = … cm3 (ii) A student suggested that using a burette to measure the 25.0 cm3 of acid would give a more accurate result than using a pipette. The percentage error of a 25.0 cm3 pipette is 0.24 %. Is the student correct? Explain your answer. … … … [2] (f) A student decided to use a 25.0 cm3 pipette instead of a measuring cylinder to measure the volume of FB 4 in Step 2. State and explain whether this alteration will improve the accuracy of the calculation of the percentage by mass of sodium ethanedioate in the mixture. … … … [1] [Total: 25]

7 9701/34/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use 2 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 full name or correct formula of the reagent must be given. (a) Compounds FB 5, FB 6 and FB 7 contain the same non-metal but in three different oxidation states. You are provided with solid samples of FB 5, FB 6 and FB 7. Carry out the tests described below and record your observations in the table. test observations (i) To 1 cm depth of dilute hydrochloric acid in a test-tube add a small spatula measure of FB 5. (ii) To 1 cm depth of dilute sulfuric acid in a boiling tube add the same depth of aqueous potassium iodide. Add a small spatula measure of FB 5. (iii) To 1 cm depth of dilute sulfuric acid in a test-tube add about ten drops of aqueous potassium manganate(VII). Add a small spatula measure of FB 5.

8 9701/34/M/J/12 © UCLES 2012 For Examiner’s Use test observations (iv) Place a small spatula measure of FB 6 into a hard glass test-tube. Heat the contents gently. (v) Place a small spatula measure of FB 6 into a boiling tube. Dissolve the solid in 1 cm depth of distilled water. Add 1 cm depth of aqueous sodium hydroxide. Warm the mixture with care. (vi) Place a small spatula measure of FB 7 into a hard glass test-tube. Heat the contents gently at fi rst, then heat more strongly. Allow to stand for a few minutes (vii) Place a small spatula measure of FB 7 into a boiling tube. Dissolve the solid in about 1 cm depth of distilled water. Add 1 cm depth of aqueous sodium hydroxide. Warm the mixture with care. [6] (b) (i) From your observations in (a), identify the non-metal present in FB 5, FB 6 and FB 7. … (ii) Suggest the oxidation state of the non-metal in FB 5 and FB 6. The oxidation state of the non-metal in FB 5 is … The oxidation state of the non-metal in FB 6 is … (iii) Suggest the type of reaction occurring in (a)(iii). … [3] I II III IV V VI

9 9701/34/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use I II III IV V VI (c) Solid compounds containing Fe2+ and Ni2+ are usually green. One of these ions is present in FB 8 and the other in FB 9. Both FB8 and FB9 are aqueous solutions. (i) Use the Qualitative Analysis Notes on page 10 to select two reagents that, used in separate tests, could identify the presence of the Fe2+ ion. The reagents are … and … (ii) Use your chosen reagents to carry out tests on both FB 8 and FB 9. Record your results in an appropriate form in the space below. (iii) From the results of the tests in (ii), state which solution contains the iron(II) ions. Fe2+ ions are contained in solution … . Explain how your observations support your conclusion. … … (iv) Aqueous EDTA is a reagent used to identify some transition metals. To 1 cm depth of the solution containing the nickel(II) ion, add 1 cm depth of aqueous EDTA. observation … … (v) State what you would expect to see if acidifi ed potassium manganate(VII) was added to a sample of the solution containing the iron(II) ion. Do not carry out this experiment. expected observation … … [6] [Total: 15]

10 9701/34/M/J/12 © UCLES 2012 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 9701/34/M/J/12 © UCLES 2012 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

12 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. 9701/34/M/J/12 © UCLES 2012 BLANK PAGE

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2012 question paper for the guidance of teachers 9701 CHEMISTRY 9701/34 Paper 32 (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 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 2012 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 2012 9701 34 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total 1 (a) MMO Collection PDO Layout PDO Recording MMO Collection Decisions I Two rough titres recorded. II Single table for each titration (step 1 and 2) Minimum of 2 × 2 “boxes” III Initial and final burette readings unambiguously recorded for rough and accurate titrations carried out. IV Correct headings and units in both titration tables. Acceptable headings: initial/final or 1st/2nd (burette) (reading)/(volume)//(reading at)/(volume at) start/finish; volume added/used/titre; or wtte, not difference, total volume or volume FB 1 Acceptable units are solidus: /cm3; brackets: (cm3); in words: volume in cubic centimetres, volume in cm3. If units are not included in the heading every entry in the table must have the correct unit. V All accurate burette readings 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.(00) VI Two burette readings within 0.10 cm3 in each titration step. Do not allow the Rough even if ticked. 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 other has also been carried out. Mark not awarded if any accurate reading is given to zero dp apart from initial ‘0’. 1 1 1 1 1 1 Step 1: Examiner subtracts candidate’s titre (corrected to 0.01 cm3) from supervisor’s titre MMO Quality Award VII, VIII, IX if δ ≤ 0.1 cm3 Award VII, VIII if 0.10 < δ ≤ 0.20 cm3 Award VII if 0.20 < δ ≤ 0.40 cm3 If Supervisor’s titre < 10.00 cm3 then halve the tolerances Spread penalty (see below) 1 1 1 Step 2: Examiner subtracts (corrected) candidate’s titre from supervisor’s titre. Check and correct titre as above.

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 34 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total 1 (a) cont. MMO Quality Award X, XI, XII if δ ≤ 0.20 cm3 Award X, XI if 0.20 < δ ≤ 0.40 cm3 Award X only if 0.40 < δ ≤ 0.80 cm3 If Supervisor’s titre < 10.00 cm3 then halve the tolerances Apply spread penalty to each of steps 1 and 2 as follows: titres selected (by examiner) differ by > 0.50 cm3 = –1; Apply a spread penalty of –1 if only one accurate titration is performed. 1 1 1 [12] (b) ACE Conclusion Interpret- ation (i) Check mean titre correctly calculated from clearly selected values (ticks or working) (ii) C2O4H2 + 2NaOH → C2O4Na2 + 2H2O (iii) Correctly calculate {(b)(i) × 0.10}/1000 and (iv) (iii)/2 (ecf from equation) 1 1 [2]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 34 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total (c) ACE Interpret- ation PDO Display I (i) Calculation of mean for (b)(i) and (c)(i) 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. Example: 26.667 must be rounded to 26.67. Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for 0.025 or 0.075 e.g. 26.325; allow mean to 1 dp if all accurate burette readings were given to 1 or zero dp and the mean is exactly correct. e.g. 26.0 and 26.2 = 26.1 is correct but 26.0 and 26.1 = 26.1 is incorrect. Do not award this mark if: any selected titre is not within 0.20 cm3 of any other selected titre unless a spread penalty has been applied or two pairs of accurate titres shown (e.g. 21.1, 21.2, 21.4, 21.5 should have a mean of 21.3); the rough titre was used to calculate the mean; the candidate carried out only 1 accurate titration in both steps 1 and 2; burette readings were incorrectly subtracted to obtain any of the accurate titre values. 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. II Correctly calculates (ii) (c)(i) × 0.02/1000 and (iii) (c)(ii) × 5/2 III (iv) Expression (c)(iii) – (b)(iv) IV Working in the correct direction is shown in any 4 steps of (b)(iii) and (iv), (c)(ii), (iii) and (iv) 1 1 1 1 [4]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 34 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total (d) ACE Interpret- ation Conclusion PDO Display I Correct Mr in both (i) 90(.0) and (ii) 134(.0) Allow ecf from misprint in (ii) of 102(.0) II Correct calculation of (i) C2O4H2 = (b)(iv) × 90.0 (allow ecf) and (ii) C2O4Na2 = (c)(iv) × 134.0 (allow ecf) [Default values: (i) 0.05859/0.0586; (ii) 0.05534/0.0553 or 0.04213/0.0421] If one of (d)(i) or (d)(ii) is fully correct then one mark may be awarded. i.e. mark horizontally or vertically III (iii) Expression {mass C2O4Na2 in (ii)/total mass} × 100 [total mass = (d)(i) + (d)(ii)] If × 100 missing from expression then correct % needed IV Final answer to each step attempted of (b)(ii), (iv), (c)(ii), (iii),(iv) and (d)(i), (ii), (iii) to 3 or 4 sf (minimum 5 steps) 1 1 1 1 [4] (e) ACE Interpret- ation (i) (±)0.05 cm3 (ii) (i) × 2 (ecf) so burette less accurate/ student incorrect use of {0.10/25} × 100 or (±)0.06 compared with (±)0.10 1 1 [2] (f) ACE Improve- ment No improvement as acid in excess 1 [1] [Total: 25]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 34 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total FB 5 = NaNO2; FB 6 = NH4Cl ; FB 7 = NaNO3; FB 8 = NiSO4(aq); FB 9 = FeSO4(aq) 2 (a) MMO Collection I (i) effervescence/bubbling/fizzing and either brown gas or blue solution II (ii) (colourless) solution (turns) yellow/orange/red- brown/brown or forms black/dark grey ppt/solid III (iii) (purple) solution/KMnO4 turns colourless/blue or solution remains colourless/turns blue IV (iv) solid sublimes//solid/ppt reforms (on cooler part of tube)//white solid/ppt further up tube V (v) gas/NH3 turns (damp) red litmus blue and no reaction in (vii) (ignore bubbling/ etc. on heating) (If gas not tested in (v) but is in (iv) then mark may be awarded provided NH3 appears in (v)) VI (vi) gas relights glowing splint or solid melts/dissolves/forms solution and pale yellow/white/cream/off-white solid/ppt forms on cooling 1 1 1 1 1 1 [6] (b) ACE Conclusion (i) N from single correct obs [brown gas (i)(ii)(iii)/blue solution (i)(iii)/ NH3 (iv)(v)/O2 (vi)] (allow N2) (ii) FB 5 +3 FB 6 –3 (iii) redox/oxidation and reduction// oxidation of N/NO2 –//reduction of Mn/MnO4 – 1 1 1 [3]

Page 7 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 34 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total (c) MMO Decisions PDO Layout MMO Collection ACE Conclusion MMO Collection I (i) NaOH and NH3 Allow KMnO4 and/or K2Cr2O7 II (ii) Tabulated with no repeated headings Allow from incorrect reagents but do not award if extra reagent introduced. III Both give green ppt with NaOH. FB 8 blue solution with NH3 (not dark blue) FB 9 green ppt with NH3 FB 8 no change/no reaction with KMnO4 and K2Cr2O7 FB 9 (KMnO4) turns yellow/decolourised/yellow- brown/orange; (K2Cr2O7) turns green/yellow-green Allow Fe(OH)2 ppt as dirty or dark green IV (iii) Fe2+ = FB 9 from green/etc. ppt insol in excess NH3 (ora) (= 2 obs) or green/etc. ppt turning brown in NH3 (= 2 obs) green/etc. ppt with NH3 (= 1 obs) (positive MnO4 – = 1 obs) (positive Cr2O7 2– = 1 obs) Evidence must match observations in (ii) V (iv) (green) solution/turns blue (Ni2+) allow towards blue e.g. cyan If Fe2+ = FB 8 in (iii) then ecf obs: solution/turns (pale) yellow/no reaction/no change VI (v) (purple)/KMnO4 turns yellow/decolourised/yellow- brown/orange 1 1 1 1 1 1 [6] [Total: 15]