Cambridge A Level Chemistry 9701 — 2009 Oct/Nov Paper 3 · Variant 4

This document consists of 9 printed pages and 3 blank pages. DC (SJF5337) 11762/3 © UCLES 2009 [Turn over * 8 5 1 2 4 1 6 5 6 8 * 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 are advised to show all working in calculations. Use of a Data Booklet is unnecessary. Qualitative Analysis Notes are printed on pages 9 and 10. 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 Paper 34 Advanced Practical Skills October/November 2009 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions For Examiner’s Use 1 2 3 Total Session Laboratory

3 9701/34/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use 1 Read through question 1 before starting any practical work. You are provided with the following reagents. • FB 1, hydrated copper(II) sulfate • FB 2, aqueous copper(II) sulfate • FB 3, aqueous sodium thiosulfate • FB 4, aqueous potassium iodide • FB 5, starch indicator solution The formula of hydrated copper(II) sulfate is CuSO4.xH2O where x shows the number of molecules of water of crystallisation present. The value of x can be found by two different methods. Method 1 involves heating to drive off water of crystallisation while Method 2 uses a titration to determine the concentration of Cu2+(aq). (a) Method 1 • Weigh a crucible and record the mass. • Add between 2.50 g and 2.70 g of FB 1 and record the new mass. • Place the crucible containing FB 1 on a pipe clay triangle and heat gently for about four minutes with a Bunsen burner. • Allow the crucible to cool. You should continue with Method 2 while the crucible is cooling. • Weigh the crucible and its contents. Record all masses in the space below. [3] (b) Calculate the mass of water lost and the mass of copper(II) sulfate that remained after heating. mass of water lost = …………… g mass of copper(II) sulfate remaining = …………… g [1]

4 9701/34/O/N/09 © UCLES 2009 For Examiner’s Use (c) Use your answer to (b) to calculate how many moles of water were lost and the moles of copper(II) sulfate, CuSO4, remaining after heating. Show all of your working. [Ar : Cu, 63.5; H, 1.0; O, 16.0; S, 32.1] The hydrated copper(II) sulfate contained …………………………… mol of water and …………………………… mol of CuSO4. [2] (d) Use your answer to (c) to determine the value of x in the formula of hydrated copper(II) sulfate, CuSO4.xH2O. x = ……………….. [2] (e) Method 2 • Fill the burette with FB 3, aqueous sodium thiosulfate. • Pipette 25.0 cm3 of FB 2 into a conical flask and use a measuring cylinder to add 10 cm3 of FB 4. • Titrate this solution with FB 3 from the burette until the mixture becomes yellow- brown. Do not add too much FB 3 at this stage. • An off-white precipitate is also present in the flask and this will mask the colour of the solution. • Add approximately 1 cm3 of FB 5. The solution will become blue-black as a starch iodine complex is formed. • Continue the titration until the blue-black colour of the complex just disappears leaving the off-white precipitate. • Perform sufficient further titrations to obtain accurate results. • Record your titration results in the space below. Make certain that your recorded results show the precision of your working. Summary 25.0 cm3 of FB 2 reacted with ………….……. cm3 of FB 3. Show which results you used to obtain the value of the volume of FB 3 by placing a tick (✓) under the readings used in your results. [11] i ii iii iv v vi vii viii ix x xi

5 9701/34/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (f) (i) In Method 1 a student was advised to carry out all weighings using the same balance. What type of error might be introduced if more than one balance was used? … …[1] (ii) In Method 2, 10 cm3 of FB 4 was added during the titration process. Assume that the measuring cylinder used could be read to ± 0.5 cm3. Calculate the percentage error in the measurement of this volume. ………….. % error [1] (g) Method 1 is usually less accurate than Method 2 for finding the value of x in the formula of hydrated copper(II) sulfate, CuSO4.xH2O. A group of students carried out Method 1 correctly but calculated a value of 4 for x. The true value for x is 5. Suggest an error in the practical procedure of the experiment that could account for this difference. … … [1] (h) Suggest a modification that could be made to the practical procedure in Method 1 to reduce this error. Explain why this modification should give an answer nearer to 5. modification … … explanation … … [2] [Total: 24]

6 9701/34/O/N/09 © UCLES 2009 For Examiner’s Use 2 In this question you should use information from the Qualitative Analysis Notes on pages 9 and 10. (a) Solutions FB 6, FB 7 and FB 8 are known to be either chlorides or sulfates of aluminium, magnesium or calcium. The addition of aqueous sodium hydroxide and aqueous ammonia can be used to give information about the cation present. Add NaOH(aq) and NH3(aq) separately to each of the solutions FB 6, FB 7 and FB 8. Rinse and reuse test-tubes where possible. Record both the tests and your observations in an appropriate form in the space below. From your observations identify the solutions containing aluminium, magnesium and calcium ions. In each case give evidence to support your answer. Solution ……………… contains the aluminium ion. supporting evidence … Solution ……………… contains the magnesium ion. supporting evidence … Solution ……………… contains the calcium ion. supporting evidence … [7] i ii iii iv v vi vii

7 9701/34/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (b) Choose a pair of reagents that, used together, would identify which solution or solutions contain(s) the sulfate ion. Carry out the tests and record, in the space below, the reagents used and the observations made. The sulfate ion is present in …………………………… . [2] [Total: 9]

8 9701/34/O/N/09 © UCLES 2009 For Examiner’s Use 3 (a) You are to carry out the tests given in the table below on solid FB 9. Record details of any gases that are released in the reactions. These gases should be identified by a test, described in the appropriate part of the table. No additional tests should be attempted. test observations (i) Place a spatula measure of FB 9 in the small hard-glass test-tube labelled FB 9 and heat the solid strongly. (ii) To 1 cm depth of aqueous sodium hydroxide in a boiling-tube, add 1 spatula measure of FB 9, then gently heat the mixture, do not boil Care is needed when heating aqueous sodium hydroxide. (iii) To 1 cm depth of aqueous sodium hydroxide in a boiling-tube, add 1 spatula measure of FB 9 and a piece of aluminium foil, then gently heat the mixture. Care is needed when heating aqueous sodium hydroxide. [4] (b) What elements must be present in FB 9 to give the results you have obtained in test (i) and test (iii)? … [1] (c) What is the function of the aluminium foil in test (iii)? … [1] (d) Do not carry out this test What would you expect to see if 1 cm depth of dilute hydrochloric acid was added to a spatula measure of FB 9? … … [1] [Total: 7]

9 9701/34/O/N/09 © UCLES 2009 [Turn over Qualitative Analysis Notes Key: [ ppt. = precipitate. ] 1 Reactions of aqueous cations reaction with NaOH(aq) NH3(aq) aluminium, Al3+(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.]

10 9701/34/O/N/09 © UCLES 2009 2 Reactions of anions ion reaction carbonate, CO3 2– CO2 liberated by dilute acids chromate(VI), CrO4 2– (aq) yellow soln 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) (insoluble in excess dilute strong acid); gives white ppt. with Pb2+(aq) sulfite, SO3 2– (aq) SO2 liberated with dilute acids; gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acid) 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 9701/34/O/N/09 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 October/November 2009 question paper for the guidance of teachers 9701 CHEMISTRY 9701/34 Paper 34 (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 October/November 2009 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 A/AS LEVEL – October/November 2009 9701 34 © UCLES 2009 Question Sections Indicative material Mark 1 (a) PDO Layout MMO Collection Three weighings recorded unambiguously Mass used between 2.50 g and 2.70 g (for all experiments; checked by examiner) Mass decreases after heating in a single experiment (ignore heating to constant mass) 1 1 1 [3] (b) ACE Interpretation Correct subtraction from experimental results in (a) for mass of water lost and for mass of residue (Correct for any experiment or for average) 1 [1] (c) PDO Display Shows working using values in (b) (can be ecf): mass of salt/159.6 and mass of water/18 (or candidate’s values for Mr) Correct calculation of each value and must have between 2 and 4 sf and correct rounding (NO ecf from incorrect Mr) 1 1 [2] (d) ACE Interpretation PDO Display Values from (c) shown in correct calculation or ratio or correct evaluation from calculation (no calculation or ratio) showing dp and correct rounding for dp shown Value of x given as an integer allow 0.5 to go up or down. (Ecf allowed) Correct answer alone (integer) and no expression or calculation shown can only gain the second mark. 1 1 [2] (e) PDO Layout PDO Recording MMO Decisions MMO Quality (i) Tabulates minimum of the burette readings or minimum of two titres (lines not needed) (ii) Records initial and final burette readings and volume of FB 3 run from burette (Don’t award if readings inverted or final is 50, 50.0 or 50.00 more than once) (iii) Appropriate headings and units for data given. (Only acceptable headings: initial/final or 1st/2nd (burette) reading; reading at start/finish; volume added; volume used; titre. Only acceptable presentation of units is solidus /cm3; brackets (cm3) or “volume in cubic centimetres” or “volume in cm3”) If units not included with heading, every entry in table must have a correct unit. (iv) All burette readings other than that labelled “rough” recorded consistently to nearest .05cm3 (v) Two uncorrected titres within 0.1 cm3 (can include rough) (vi), (vii), (viii) and (ix) Check and correct titre subtractions where necessary. Examiner selects the best mean titre (treat as accurate unless labelled “rough” or to fewer dp) and compares to Supervisor: Apply a hierarchy: 2 identical, titres within 0.05 cm3, titres within 0.10 cm3 etc. Award (vi), (vii), (viii) and (ix) for: a titre within 0.20 cm3 1 1 1 1 1 4

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 34 © UCLES 2009 Question Sections Indicative material Mark MMO Decisions PDO Display Award (vi), (vii), (viii) only for: a titre of 0.20+ cm3 to 0.30 cm3 Award (vi) and (vii), only for: a titre of 0.30+ cm3 to 0.50 cm3 Award (vi) only for: a titre of 0.50+ cm3 to 0.80 cm3 Apply spread penalty as follows: titres selected (by examiner) differ > 0.20 cm3 but ≤ 0.50 cm3 = –1; titres > 0.50 cm3 = –2 from marks awarded in (vi) to (ix) (no negative marks) Apply a spread of –2 if only one titration is performed or single value selected. (x) Selects (and ticks – but some indication must be shown) at least two titres for calculation of mean titre, all titres used to be within 0.2 cm3 (xi) Correct mean displayed to same number of decimal places as most precise burette reading (If initial reading 0 use to dp of final) (If titres 0.05 apart then 0.025 or 0.075 is acceptable) 1 1 [11] (f) ACE Interpretation (i) Systematic error, non–consistent zero or wtte or different precision of balance (just!) (ii) Correct calculation of maximum % error (0.5/10 x 100 =) 5% 1 1 [2] (g) ACE Conclusions (Mass loss is too low) Candidate suggests (i) insufficient heating or (ii) solid reabsorbs moisture on cooling 1 [1] (h) ACE Improvement (i) Heating to constant mass (could be in explanation, possible ecf from (g)) Or (ii) Cooling in desiccator / cooling with lid on crucible or (iii) Grinding/crushing before heating provided candidate makes clear that not all water driven off (as not heated long enough) Explains that mass loss or wtte is too low and how modification will reduce this Reference to mass loss being too low may be in (g). 1 1 [2] Qn 1 Total [24] FB 6 is MgCl2(aq); FB 7 is Al2(SO4)3 (aq); FB 8 is CaCl2

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 34 © UCLES 2009 Question Sections Indicative material Mark 2 (a) MMO Collection ACE Conclusions ACE Interpretation (i) For FB 6 NaOH – a white ppt* insoluble in excess NH3(aq) – white ppt insoluble in excess (ii) For FB 7 NaOH – a white ppt soluble in excess NH3(aq) – white ppt insoluble in excess (iii) For FB 8 NaOH – a white ppt insoluble in excess NH3(aq) – no precipitate (iv) FB 7 contains Al 3+ (v) FB 6 contains Mg2+ (vi) FB 8 contains Ca2+ ecf only for these ions and from white ppts only (iv), (v), (vi) cannot be awarded if any of the relevant observations are incorrect (vii) Gives appropriate evidence for identification of at least two ions (any 2). Minimum statement required: Al 3+ – (white) ppt soluble in excess NaOH; Mg2+ – (white) ppt insoluble in excess NaOH and (white) ppt with NH3; Ca2+ – no ppt with NH3. No colour ppt other than white but colour of ppt may be taken from observations 1 1 1 1 1 1 1 [7] (b) MMO Decisions MMO Collection Add (aqueous) barium chloride** (nitrate) and three correct observations Any white precipitate (from above) insoluble in HCl or HNO3 (Acid name may be in 1st part of answer) 1 1 [2] Qn 2 Total [9] *solid (formed) **Ba2+ (aq) or aqueous barium ions FB 9 is NaNO3

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 34 © UCLES 2009 Question Sections Indicative material Mark 3 (a) MMO Collection ACE Conclusion Gas evolved relights a glowing splint in test (i) No reaction/no gas given off in test/only (see) solid dissolving (ii) Gas turning red litmus blue evolved on heating with NaOH and Aluminium foil in test (iii) Oxygen evolved or NO2 evolved from brown gas in (i) and ammonia gas evolved in (iii) based on correct observations (no ecf) 1 1 1 1 [4] (b) ACE Conclusions Nitrogen and oxygen ecf allowed for (i) if also hydrogen from “pops with lighted splint” 1 [1] (c) ACE Conclusions States that aluminium foil is a reductant/reducing agent 1 [1] (d) MMO Decisions No reaction if nitrate Colourless gas, turning brown in air or brown gas if nitrite Link back to (b) if single ion given (e.g. if only NO3 – in (b) then give mark for “no reaction”) 1 [1] Qn 3 Total [7]