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

This document consists of 10 printed pages and 2 blank pages. DC (SJF5336) 11751/4 © UCLES 2009 [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 are advised to show all working in calculations. 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. * 7 3 4 6 6 6 4 6 5 5 * CHEMISTRY 9701/33 Paper 33 Practical Test 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 9701/33/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. • FA 1, hydrated iron(II) sulfate • FA 2, aqueous iron(II) sulfate • FA 3, aqueous potassium manganate(VII) • FA 4, sulfuric acid The formula of hydrated iron(II) sulfate is FeSO4.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 Fe2+(aq). (a) Method 1 • Weigh a crucible and record the mass. • Add between 1.80 g and 2.00 g of FA 1 and record the new mass. • Place the crucible containing FA 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 iron(II) sulfate that remained after heating. mass of water lost = …………… g mass of iron(II) sulfate remaining = …………… g [1]

4 9701/33/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 iron(II) sulfate, FeSO4, remaining after heating. Show all of your working. [Ar : Fe, 55.8; H, 1.0; O, 16.0; S, 32.1] The hydrated iron(II) sulfate contained …………………………… mol of water and …………………………… mol of FeSO4. [2] (d) Use your answer to (c) to determine the value of x in the formula of hydrated iron(II) sulfate, FeSO4.xH2O. x = ……………….. [2] (e) Method 2 • Fill the burette with FA 3, aqueous potassium manganate(VII). • Pipette 25.0 cm3 of FA 2 into a conical flask and use a measuring cylinder to add approximately 20 cm3 of FA 4. • Titrate this solution with FA 3 from the burette until the first permanent pink colour remains in the solution. • 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 FA 2 reacted with ………….……. cm3 of FA 3. Show which results you used to obtain the value of the volume of FA 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 9701/33/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (f) All experimental methods contain errors, some of which are concerned with uncertainty of measurements. Complete the table below to show the uncertainties in measuring the volume of potassium manganate(VII) used in Method 2. maximum uncertainty in a single reading with a burette ……………… cm3 volume of potassium manganate(VII), FA 3, from the summary in (e) ……………… cm3 maximum percentage error in the volume of potassium manganate(VII) used ……………… % [2] (g) Method 1 is usually less accurate than Method 2 for finding the value of x in the formula of hydrated iron(II) sulfate, FeSO4.xH2O. A group of students carried out Method 1 correctly but calculated a value of 9 for x. The true value for x is 7. 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 7. modification … … explanation … … [2] [Total: 24] BEFORE STARTING QUESTION 2, heat a half-full 250 cm3 beaker of water for use as a hot water-bath in question 3.

6 9701/33/O/N/09 © UCLES 2009 For Examiner’s Use 2 The four solutions FA 5, FA 6, FA 7 and FA 8 each contain one of the following anions. • chloride, Cl – • iodide, I– • nitrate, NO3 – • nitrite, NO2 – Use information from the Qualitative Analysis Notes on page 11 to answer the following questions. (a) Which single reagent could you use to identify the solution containing the nitrite ion? … Which single reagent could you use to identify the solutions containing the chloride and the iodide ion? …[1] (b) Use the reagents selected in (a) to test each of the solutions. Rinse and reuse test-tubes where possible. Record in an appropriate form in the space below, the reagents used and the observations made. From your observations identify the solutions containing chloride, iodide and nitrite ions. In each case give evidence to support your answer. solution ……………… contains the chloride ion. supporting evidence … solution ……………… contains the iodide ion. supporting evidence … solution ……………… contains the nitrite ion. supporting evidence … [7] i ii iii iv v vi vii

7 9701/33/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (c) Do not carry out this test. State another test that you could use to confirm the presence of chloride and iodide ions. … …[1] [Total: 9]

8 9701/33/O/N/09 © UCLES 2009 For Examiner’s Use 3 (a) You are to carry out the tests given in the table below on solutions FA 9 and FA 10. You should record details of colour changes seen and the formation of any precipitate. No additional tests should be attempted. Reheat your water bath until the water boils. Turn off the Bunsen burner. test observations (i) To 1 cm depth of FA 9 in a test-tube, add 1 cm depth of dilute hydrochloric acid. (ii) To 1 cm depth of FA 9 in a test-tube, add 1 cm depth of dilute sulfuric acid. (iii) To 1 cm depth of FA 10 in a boiling-tube, add dilute sulfuric acid until no further change occurs. Use this solution for test (iv). (iv) To the solution left after test (iii) add 1 cm depth of ethanol. Place the mixture in your hot water bath and leave for approximately 3 minutes. (v) To 1cm depth of FA 9 in a test-tube add 1 cm depth of FA 10. [4]

9 9701/33/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (b) From your observations in (a) identify the cation present in FA 9. Give evidence to support your answer. Solution FA 9 contains the ……………… ion. supporting evidence … …[2] (c) What chemical change, involving ethanol, takes place in reaction (iv)? Give evidence to support your answer. chemical change … supporting evidence … …[1] [Total: 7]

10 9701/33/O/N/09 © UCLES 2009 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.]

11 9701/33/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 9701/33/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 9701/33 Paper 33 (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 33 © UCLES 2009 Question Sections Indicative material Mark 1 (a) PDO Layout MMO Collection Three weighings recorded unambiguously (words needed) Mass used between 1.80 g and 2.00 g (for all experiments) Mass decreases after heating in a single experiment attempted (no repeat experiment allowed) (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 attempted or for an average) 1 [1] (c) PDO Display ACE Interpretation Shows working using values from (b) (can be ecf): mass of salt/151.9 and mass of water/18 or candidate’s value of Mr Correct calculation of each value and must have between 2 and 4 sf and correct rounding (NO ecf from incorrect Mr but ecf allowed from masses used in first part) 1 1 [2] (d) ACE Interpretation PDO Display Values from (c) shown in correct calculation or ratio or value of correct calculation showing dp and correct rounding for sf shown Value of x for fully correct answer given as an integer allow 0.5 to go up or down (ecf allowed) (If correct integer shown but no expression or calculation is shown award second mark only) 1 1 [2]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 33 © UCLES 2009 Question Sections Indicative material Mark (e) PDO Layout PDO Recording MMO Decisions MMO Quality MMO Decisions (i) Tabulates minimum of two pairs of burette readings or at least two titres (lines not needed) (ii) Records initial and final burette readings and volume of FA3 run from the burette (Do not award if readings inverted or final is 50. 50.0, 50.00 more than once, or initial value is 50.00) (iii) Appropriate headings and units for data given. (Only acceptable headings are: initial/final, first/second (burette) reading; reading at start/finish; volume added/used or wwte; 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 0.05 cm3) (v) Two uncorrected titres within 0.1 cm3 (can include rough) (vi), (vii), (viii) and (ix) Check and correct titre subtractions where necessary. (If there are any showing greater precision than to 0.05, correct to the nearest 0.05 cm3) Examiner selects the best mean titre (treat as accurate unless labelled rough or to fewer dp but if rough is ticked or selected by candidate it can be considered) and compared 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 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 > 0.2 but ≤ 0.5 cm3 = –1; titres > 0.5 cm3 = –2 from the marks awarded in (vi) to (ix) (no negative marks). Apply a spread penalty of –2 if only one titration is performed or a single value is selected by examiner (e.g. rough + one other) (x) Selects (and ticks) at least two titres for calculation of mean titre (some indication must be made of which ones used). The spread of any titres used must not exceed 0.20 cm3 (continued) 1 1 1 1 1 4 1

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 33 © UCLES 2009 Question Sections Indicative material Mark (e) continued PDO Display (xi) Correct mean displayed to same number of decimal places as burette readings (If any burette reading is to 2 dp then mean to 2 dp; if two titres 0.05 apart then 0.025 or 0.075 is acceptable; similarly if titres recorded to1 dp then 0.05; to no dp then to 0.5. If three titres used giving mean of 0.033... or 0.066... then allow mean to nearest 0.05) 1 [11 ] (f) ACE Interpretation Maximum error for single reading of burette given as 0.05 cm3 (even if readings recorded to 1 dp) Correct calculation to 2 sf (minimum) showing correct rounding of maximum % error 2 x candidate’s error/titre x 100 or allow 0.10/titre x100 if 0.1 in first box. 1 1 [2] (g) ACE Conclusions Mark (g) and (h) as a single unit (Mass loss is too high) Candidate suggests spitting or decomposition or overheating/heating too long (The latter will not gain any other mark unless a consequence of overheating is given.) 1 [1] (h) ACE Improvement Use of lid or gentle heating (at first) – to reduce spitting/loss of solid or reduced temperature or heat for a shorter time – to prevent decomposition Explains that mass loss is too high or wtte (e.g. some solid spits out) and how modification will reduce this or a realisation that something other than water is lost. 1 1 [2] Qn 1 Total [24]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 33 © UCLES 2009 Question Sections Indicative material Mark FA 5 is NaNO2(aq); FA 6 is NaCl (aq); FA 7 is KI; FA 8 is distilled water 2 (a) MMO Decisions Chooses a named (dilute) strong acid to identify the nitrite (name could be in (b)). and Chooses silver nitrate or lead nitrate to identify the chloride and iodide (Ag+ (aq) or aqueous solution of silver ions accepted, ditto lead ions) [1] (b) MMO Collection ACE Conclusions ACE Interpretation (i) Records a brown gas from FA 5 and acid and no reaction with second reagent. (ii) Records a colourless or blue solution on adding acid to FA5 (iii) Records a white precipitate when Ag+ or Pb2+ is added to FA 6 and no reaction with acid (iv) Records a yellow precipitate when Ag+ or Pb2+ is added to FA 7 and no reaction with acid. If acid alone used and all four observations are correct (i) and (ii) and identity mark (v) can be awarded. If AgNO3 or Pb(NO3)2 only used and all four observations are correct then can award (iii) and (iv) and identity mark (vi). If a white ppt is recorded with FA5 and all other observations are correct award (iii) and (iv) but then deduct one observation mark for the FA5 result. (Annotate the paper near the boxes.) Mark (vi) would be available to a candidate concluding both FA5 and FA6 are Cl – and FA7 is I –. If a spurious reagent is chosen in (a) ignore and mark other (if correct) as single reagent. If three reagents are used, mark the observations for acid and the first of Ag+ or Pb2+ mentioned in (a). Deduct one mark (from (i) – (iv)) if erroneous observation with FA8 or test not done. A dash is similarly penalised (once, at the first opportunity) (v) and (vi) are consequent on observations (v) Identifies nitrite in FA 5 Allow from effervescence or bubbling from FA5 + acid only. (vi) Identifies chloride in FA 6 (only, unless single reagent as above) and iodide in FA 7 (vii) Gives appropriate evidence for identification of all three ions (consequential on observations) (Brown gas with acid + FA5 needed here.) 1 1 1 1 1 1 1 [7] (c) MMO Decisions Add (aqueous) ammonia to the precipitate formed with silver nitrate or Add (aqueous) lead nitrate or silver nitrate (to a fresh sample of) the solution Do not penalise lack of (aq) with an ion if already penalised in (a) 1 [1] Qn 2 Total [9]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 33 © UCLES 2009 Question Sections Indicative material Mark FA 9 is Pb(NO3)2, FA 10 is K2CrO4 3 (a) MMO Collection White ppt formed in tests (i) and (ii) and yellow ppt in test (v) (no variation on white; ppts not soluble in excess acid) Solution changes from yellow to orange (both colours and ‘solution’ needed) in (iii) (Solution) changes to green or blue (blue/green, cyan, turquoise but no orange or orange–brown as final colour) in (iv) Ignore state 1 1 1 [3] (b) ACE Conclusions FA 9 contains the cation Pb2+ or lead II (all three ppts must be in (a) but ignore any PbCl2 ppt redissolving; no Ba2+ unless no ppt with HCl) (White) ppt with both HCl and H2SO4 given as evidence or yellow ppt with FA10 named as chromate or CrO4 2– 1 1 [2] (c) ACE Conclusions States that ethanol is being oxidised or is reducing agent or reduces FA10 Ethanol oxidised to ethanal or alcohol oxidised to aldehyde or chromate VI reduced to chromium III or dichromate reduced to chromium III 1 1 [2] Qn 3 Total [7]