Cambridge A Level Chemistry 9701 — 2012 May/June Paper 3 · Variant 3

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 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. CHEMISTRY 9701/33 Advanced Practical Skills 1 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 12 printed pages. [Turn over IB12 06_9701_33/5RP © UCLES 2012 *0014911874* Session Laboratory For Examiner’s Use 1 2 Total

2 9701/33/M/J/12 © UCLES 2012 For Examiner’s Use 1 You are to determine the percentage purity of a sample of calcium carbonate. This experiment involves three steps. In step one, you will react the impure calcium carbonate with an excess of acid. In step two, you will carry out a titration to fi nd the amount of acid you used in step one. In step three, you will carry out a second titration to fi nd how much (excess) acid remained following the reaction in step one. Finally, you will use the values found in the three steps to calculate the percentage purity of the calcium carbonate. Assume the impurity in the calcium carbonate will not react with acid or alkali. FA 1 is 0.100 mol dm–3 sodium hydroxide, NaOH. FA 2 is approximately 1 mol dm–3 hydrochloric acid, HCl. FA 3 is FA 2 diluted by a factor of 10, approximately 0.1 mol dm–3 hydrochloric acid, HCl. FA 4 is a sample of impure calcium carbonate, CaCO3. methyl orange indicator Read through the whole method before starting any practical work. (a) Method Step 1 ● Fill the burette labelled FA 2 with FA 2. ● Run 50.00 cm3 of FA 2 into a 250 cm3 beaker. ● Weigh the tube containing the impure calcium carbonate, FA 4. ● Tip the contents of the tube, in small portions, into the acid to avoid acid spray. Stir the mixture and leave the stirring rod in the beaker. ● Reweigh the tube containing any residue. ● Record the weighings and the mass of FA 4 added in a suitable form below. Step 2 ● Fill the burette labelled FA 1 with FA 1. ● Pipette 25.0 cm3 of FA 3 into a conical flask. ● Add methyl orange indicator. ● Perform a rough titration and record your burette readings in the space below. The rough titre is … cm3.

3 9701/33/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use ● 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 FA 1 added in each accurate titration. Step 3 ● Stir the mixture from Step 1 again to ensure that all the solid has dissolved. ● Transfer the solution to the 250 cm3 graduated (volumetric) flask labelled FA 5. ● Rinse the beaker twice with a little distilled water and add the washings to the graduated flask. ● Make the solution up to 250 cm3 with distilled water. Ensure that the contents of the flask are thoroughly mixed. ● Transfer 25.0 cm3 of this solution, FA 5, into a second conical flask using a second pipette. ● 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 FA 1 added in each accurate titration. [12] I II III IV V VI VII VIII IX X XI XII

4 9701/33/M/J/12 © UCLES 2012 For Examiner’s Use Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. The equation for the reaction between sodium hydroxide and hydrochloric acid is shown below. NaOH(aq) + HCl (aq) → NaCl (aq) + H2O(l) (b) (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 FA 3 required ………….. cm3 of FA 1. (ii) Use your answer from (i) to calculate the number of moles of sodium hydroxide, FA 1, required to react with 25.0 cm3 of FA 3 in Step 2. moles of NaOH = … mol (iii) Use your answer from (ii) to determine the number of moles of hydrochloric acid in 25.0 cm3 of FA 3. moles of HCl in 25.0 cm3 of FA 3 = … mol (iv) FA 3 was produced by diluting FA 2. Calculate the number of moles of hydrochloric acid in 50.00 cm3 of FA 2. moles of HCl in 50.00 cm3 of FA 2 = … mol [2] (c) (i) From your accurate titration results in Step 3, obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. 25.0 cm3 of FA 5 required ………….. cm3 of FA 1. (ii) Use your answer from (i) to calculate the number of moles of sodium hydroxide, FA 1, required to react with 25.0 cm3 of FA 5 in Step 3. moles of NaOH = … mol

5 9701/33/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use (iii) Use your answer from (ii) to determine the number of moles of hydrochloric acid in 25.0 cm3 of FA 5. moles of HCl in 25.0 cm3 of FA 5 = … mol (iv) Use your answer from (iii) to determine the number of moles of hydrochloric acid in 250 cm3 of FA 5. moles of HCl in 250 cm3 of FA 5 = … mol [4] (d) (i) Write an equation for the reaction between calcium carbonate and hydrochloric acid. … (ii) Calculate the number of moles of hydrochloric acid that reacted with calcium carbonate in FA 4 using the following expression. moles of HCl = (b)(iv) – (c)(iv) = … mol (iii) Use your answers from (i) and (ii) to calculate the mass of CaCO3 in FA 4. [Ar: C, 12.0; O, 16.0; Ca, 40.1] (If you were unable to answer (d)(ii), you may assume that the number of moles of hydrochloric acid that reacted with calcium carbonate was 0.0351 mol.) mass of CaCO3 in FA 4 = … g (iv) Calculate the percentage purity by mass of the calcium carbonate in FA 4. The percentage purity by mass of calcium carbonate is … % [4] I II III IV I II III IV

6 9701/33/M/J/12 © UCLES 2012 For Examiner’s Use (e) (i) What is the maximum error in a single burette reading? maximum error in a burette reading = … cm3 (ii) Calculate the maximum percentage error for one of your accurate titres in Step 3. Show your working. maximum percentage error = … % [2] (f) A student decided to use a larger mass of FA 4. State and explain whether this alteration will improve the accuracy of the percentage purity obtained. … … [1] [Total: 25]

7 9701/33/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. Half fi ll a 250 cm3 beaker with water. Heat to approximately 80 °C, then stop heating. You will need this as a hot water bath in (a)(viii). (a) Compounds FA 6, FA 7 and FA 8 are salts containing the same transition metal but in three different oxidation states. You are provided with solutions of FA 6 and FA 7 and a solid sample of FA 8. Carry out the experiments described below and record your observations in the table. test observations (i) To 1 cm depth of FA 6 in a test-tube add about 5 cm depth of dilute sulfuric acid and mix the two solutions. Use this mixture for tests (ii) and (iii). no observation required (ii) To 1 cm depth of hydrogen peroxide in a test-tube add 10 drops of acidifi ed FA 6 from (i). (iii) To 1 cm depth of potassium iodide in a test-tube add 1 cm depth of acidifi ed FA 6 from (i).

8 9701/33/M/J/12 © UCLES 2012 For Examiner’s Use test observations (iv) To 1 cm depth of FA 7 in a test-tube add 1 cm depth of aqueous sodium hydroxide and allow to stand for a few minutes. (v) To 1 cm depth of FA 7 in a test-tube add aqueous ammonia until in excess. (vi) To 1 cm depth of FA 7 in a test-tube add 1 cm depth of FA 6 and allow to stand for a few minutes. (vii) To 1 cm depth of hydrogen peroxide in a test-tube add a small spatula measure of FA 8. (viii) Place a small spatula measure of FA 8 in a test-tube and add about 10 drops of concentrated hydrochloric acid with care. Place the tube in the hot water bath. Test any gas produced with damp litmus paper. When you have made your observations, fi ll the test-tube with cold water to stop any further reaction. [6] (b) (i) From your observations in (a) suggest the identity of the transition metal contained in FA 6, FA 7 and FA 8. The transition metal present in the three compounds is … Explain how your observations support your conclusion. … … … I II III IV V VI

9 9701/33/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use (ii) Suggest the type of reaction occurring in (a)(iii). … (iii) Give the oxidation state of the transition metal in FA 7. … The oxidation state of the transition metal in FA 6 is +7. Suggest an oxidation state of the transition metal in the product formed in (a)(vi). … [3] (c) Aqueous solutions FA 9 and FA 10 both contain halide ions. (i) Use the Qualitative Analysis Notes on page 12 to select two reagents which, used together, identify the halide ions in FA 9 and FA 10. The fi rst reagent is … and this is followed by … (ii) Use your chosen reagents to carry out tests on FA 9 and FA 10. Record your results in an appropriate form in the space below.

10 9701/33/M/J/12 © UCLES 2012 For Examiner’s Use (iii) From the results of the tests in (ii), state which halide each solution contains. FA 9 contains … FA 10 contains … (iv) Halides can also be identifi ed by reaction with concentrated sulfuric acid. The acid can act as an oxidising agent. State what you would expect to see if concentrated sulfuric acid was added to a solid sample of FA 9 and FA 10. Do not carry out these experiments. expected observation with FA 9 … … expected observation with FA 10 … … (v) Solutions containing the copper(II) ion react with concentrated hydrochloric acid. To a 1 cm depth of aqueous copper(II) sulfate in a test-tube, add an equal volume of concentrated hydrochloric acid with care. observation … … [6] [Total: 15] I II III IV V VI

11 9701/33/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.]

12 9701/33/M/J/12 © UCLES 2012 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. 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

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 9701/33 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 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 33 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total 1 (a) PDO Layout MMO Collection PDO Recording MMO Collection MMO Decisions I Two balance readings and mass used unambiguously recorded. II Two rough titres and burette readings recorded. III Single table for each accurate titration Minimum of 2×2 “boxes” IV Correct headings and units in weighing table and accurate titration table(s) Acceptable headings: mass of tube + FA 4; mass of tube + residue/mass of empty tube (mass of FA 4 used); initial/final or 1st/2nd (burette)(reading)/ (volume)/ (reading at)/(volume at) start/finish; volume added/used/ titre; or wtte, not “difference” or “total volume” Acceptable units are solidus:/cm3; brackets: (cm3); in words: volume in cubic centimeters, volume in cm3. Similarly for mass in g, etc. 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 uncorrected accurate titres within 0.10 cm3 in both steps Do not allow the Rough even if ticked. Do not award this mark if having performed two titres within 0.10 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 burette reading is given to zero dp apart from an initial reading of 0 1 1 1 1 1 1 (a) cont. Step 2: 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 Spread penalty (see below) 1 1 1

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 33 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total Step 3: Examiner calculates corrected candidate titre × candidate mass added supervisor mass added and subtracts the corrected value from the supervisor’s titre. If 1 g > candidate mass > 3g then use default value of 2.00 g for the Q marks and do not award one mark (from marks X to XII) (a) cont. MMO Quality Award X, XI, XII if δ ≤ 1.00 cm3 Award X, XI if1.00 < δ ≤ 2.00 cm3 Award X only if 2.00 < δ ≤ 4.00 cm3 If Supervisor’s t3 < 10.00 cm3 then halve the tolerances. Apply spread penalty to each of steps 2 & 3 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 Interpretation (i) Check mean titre correctly calculated from clearly selected values (ticks or working) no mark awarded here (ii) Expression {(b)(i) x 0.10}/1000 and (iii) as (ii) If no working shown then answer must be correct (iv) Expression (b)(iii) × 2 × 10 If no working shown then answer must be correct 1 1 [2]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 33 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total (c) ACE Interpretation 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 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 (eg 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 2 and 3; burette readings were incorrectly subtracted to obtain any of the accurate titre values. 1 II (ii) (c)(i) × 0.1/1000 and (iii) as (c)(ii) If no working shown then answer must be correct III (iv) (c)(iii) × 10 If no working shown then answer must be correct 1 1 PDO Display IV Working is shown in every step of (b)(ii) and (iv), (c)(ii) and (iv) and at least 3 steps attempted Working must be a step in the right direction 1 [4]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 33 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total (d) ACE Conclusion PDO Display ACE Conclusion PDO Display I (i) CaCO3 + 2HCl → CaCl2 + CO2 + H2O Allow H2CO3 II (iii) {(d)(ii)/2} × 100.1 If the balancing is incorrect then the value of (d)(ii) must be correct for ecf to be allowed. III (iv) expression {(d)(iii)/mass in (a)} × 100 If no working shown then answer must be correct IV Final answer to every step attempted out of (b), (c) and (d) apart from (b)(iv) to 3 or 4 sf (minimum 6 steps attempted) 1 1 1 1 [4] (e) ACE Interpretation (i) (±)0.05 cm3 (ii) {0.1/one of the titre values in step 3} × 100 (ecf (i) × 2 for error) 1 1 [2] (f) ACE Improvement Explanation must not contradict suggested improvement: larger mass reacts with more HCl so smaller titre so larger % error; larger mass may be excess and won’t dissolve in HCl; larger mass would result in smaller % mass error; greater acid spray would result in greater % error. 1 [1] [Total: 25]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 33 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total FA 6 = KMnO4(aq); FA 7 = MnSO4(aq); FA 8 = MnO2; FA 9 = KI(aq); FA 10 = NaCl(aq) 2 (a) MMO Collection I (ii) (purple) turns colourless and effervescence/fizzing/bubbling or solution turns colourless/ solution remains colourless Note: positive O2 test may be reported here II (iii) solution turns brown/red-brown/ orange/yellow or black solid (formed) 1 1 III (iv) off-white/buff/beige/pale brown ppt darkens/turns brown on standing and (v) off-white/ buff/beige/pale brown ppt insoluble in excess NH3 IV (vi) (pale) brown solution/(dark) brown ppt V (vii) effervescence and (gas) reignites glowing splint in (vii) or (ii) or gas reignites glowing splint VI (viii) (gas) bleaches (damp) litmus paper 1 1 1 1 [6] (b) ACE Conclusions (i) Mn from two pieces of evidence: FA 7 off-white/etc ppt with NaOH and NH3 or off- white/etc ppt with NaOH darkening or off-white/etc ppt with NH3 insoluble in excess allow: white/cream ppt darkening in both NaOH and NH3/white/cream ppt turning brown and insoluble in excess of either or FA 6 is purple and an oxidising agent (ii) redox or iodide/I– oxidised or manganese/manganate/Mn(VII)/MnO4 – reduced (iii) FA 7 +2 and product +3 to +6 1 1 1 [3]

Page 7 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9701 33 © University of Cambridge International Examinations 2012 Question Sections Indicative material Mark Total (c) MMO Decisions PDO Layout MMO Collection ACE Conclusions MMO Collection I (i) AgNO3(aq), then NH3(aq) (ignore HNO3) II (ii) Tabulated with no repeated headings Allow from incorrect reagents but withhold if extra reagent introduced (unless HNO3). III FA 9 yellow ppt with Ag+ insoluble in NH3 and FA 10 white ppt with Ag+ soluble in NH3 Allow correct obs for Ag+ and Pb2+ IV (iii) FA9 = iodide/I– and FA10 = chloride/Cl – Allow from correct colour of Ag+ ppt provided AgI not soluble/AgCl not insoluble in NH3 V (iv) Both correct – ecf from (iii) iodide: purple fumes/gas or black solid chloride: misty/white/steamy fumes bromide: red-brown/orange solid or red-brown vapour (not brown) VI (v) (blue) solution/turns green/yellow-green (not yellow) 1 1 1 1 1 1 [6] [Total: 15]