Cambridge A Level Chemistry 9701 — 2009 Oct/Nov Paper 3 · Variant 2

This document consists of 12 printed pages. DC (SJF4887/CG) 17559/3 © 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 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. * 0 8 3 0 9 0 7 0 0 8 * CHEMISTRY 9701/32 Paper 32 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 Total Session Laboratory

2 9701/32/O/N/09 © UCLES 2009 For Examiner’s Use 1 This question concerns the solubility of FB 1, potassium nitrate, in water. The solubility of a substance in water is defined as: the mass of substance that will dissolve in and just saturate 100g of water at a particular temperature. When a solution is saturated the dissolved solid is in equilibrium with undissolved solid. When a solution of potassium nitrate is cooled it becomes saturated when crystals form in the solution. You are to investigate how the solubility of FB 1 in water varies with temperature. You are provided with the following materials. weighing bottle, labelled FB 1, containing potassium nitrate distilled water Read through the instructions before starting any practical work. Method • Weigh an empty boiling-tube. • Add the contents of the weighing bottle labelled FB 1 to the weighed boiling-tube. • Reweigh the boiling-tube and its contents. • Record, in an appropriate form below, your weighings and the mass of FB 1 used. (a) Weighings [2]

3 9701/32/O/N/09 © UCLES 2009 [Turn over (b) Preparing a saturated solution • Fill the burette with distilled water. • Add 14.00cm3 of distilled water from the burette to the weighed boiling-tube containing FB 1. • Use the clamp as a holder for the boiling-tube. Take care not to break the tube by clamping it too tightly. • Warm the tube carefully, while stirring the contents with a thermometer, until all the solid has dissolved. (Take care that you do not break the thermometer bulb or the tube while stirring.) • Keeping the tube in the clamp attach the clamp to a stand. • Let the tube cool and continue to stir gently with the thermometer. • Watch the solution carefully. Note and record (on the next page) the temperature at which you first notice crystals forming in the solution. • If you are uncertain about the temperature when crystals first form, warm the tube again for a few moments and repeat the cooling. • As soon as you have recorded the temperature add a further 2.00 cm3 of distilled water to the tube from the burette. • Warm to redissolve the solid and cool as before. • Note and record (on the next page) the temperature at which crystals now form in the solution. This will be lower than the temperature obtained with 14.00cm3 of water. • Repeat the addition of 2.00cm3 of distilled water, the heating and the cooling, until you have four readings in total.

4 9701/32/O/N/09 © UCLES 2009 For Examiner’s Use (c) In an appropriate form in the space below, record the following. • the total volume of distilled water in the boiling-tube • the temperature at which crystals first appeared for each solution Make certain that your results show the precision of your working. [8] (d) For each solution, calculate the solubility (in grams of solid per 100g of water) using the following formula. solubility = 100 volume of water × mass of FB 1 dissolved Complete the table below to show the solubility at different temperatures. In all calculated values show appropriate significant figures. solubility (in grams of solid per 100g of water) temperature / °C [3] i ii iii iv v vi vii viii

5 9701/32/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (e) Plot solubility against temperature and draw an appropriate line through the points plotted. Do not start at zero on either axis. You will need to be able to find the solubility of FB1 at 42.5°C.

6 9701/32/O/N/09 © UCLES 2009 For Examiner’s Use From the graph plotted the solubility of FB 1 in water at 42.5°C is …………….. g of solid per 100g of water. [6] (f) Describe how the solubility of FB 1 changes with temperature. … … … [1] (g) Use your answer to (f) and your understanding of equilibrium systems to explain if dissolving FB 1, KNO3, under equilibrium conditions is exothermic or endothermic. KNO3(s) + aq KNO3(aq) … … … … [2] (h) Suggest two possible sources of inaccuracy, other than poor experimental technique, in this experiment. 1 … … … 2 … … … [2]

7 9701/32/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use (i) A solution of KNO3, saturated at 60 °C, is prepared in a thermostatically controlled water bath. The solubility of KNO3 at 60 °C can be calculated if the mass of the solution and the mass of solid dissolved in the solution can be determined. Suggest steps to enable you to find these masses. You may not need all of these numbered steps. 1 … 2 … 3 … 4 … 5 … 6 … 7 … Show how you would calculate the solubility of KNO3 at 60°C from the mass of the solution and the mass of solid dissolved in the solution. [2] [Total: 26]

8 9701/32/O/N/09 © UCLES 2009 For Examiner’s Use 2 You are provided with three solids, FB 2, FB 3, and FB 4. Each of the solids contains one cation from those on page 11 and a sulfite or sulfate anion. You will carry out specified tests to identify the cations and anions present in FB 2, FB 3 and FB 4. Use the data on pages 11 and 12. 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 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 present should be attempted. If any solution is warmed a boiling-tube MUST be used. (a) In separate boiling-tubes, dissolve half of each of the solids FB 2, FB 3 and FB 4 in a minimum volume of dilute hydrochloric acid. Gently warm each of the boiling-tubes. Add distilled water so that each boiling-tube is approximately 2/3 full. Record your observations in an appropriate form in the space below. [2] (b) The cations present in FB 2, FB 3 and FB 4 can be identified by reaction of each solution, with aqueous sodium hydroxide and with aqueous ammonia. React 1 cm depth of each of the solutions prepared in (a) with each of these two reagents. Record, in an appropriate form, in the space below your observations for these reactions. i ii iii iv v

9 9701/32/O/N/09 © UCLES 2009 [Turn over For Examiner’s Use Conclusions Using your observations you should be able to identify the cation in two of the solutions. For the remaining solution you should be able to identify two possible cations. FB 2 contains the cation(s) ………………………………. . FB 3 contains the cation(s) ………………………………. . FB 4 contains the cation(s) ………………………………. . [5] (c) Use the information on pages 11 and 12 to select a reagent to distinguish between the two possible cations identified as present in one of the solutions in (b). … Carry out the test with the selected reagent. observation … conclusion … [1] (d) In separate boiling-tubes shake the remaining half of each solid with 3 cm depth of distilled water. If any solid does not readily dissolve in water filter the mixture and retain the solution formed. You will need to keep some of the FB 2 solution for test (f). Carry out the following tests. test observations FB 2 FB 3 FB 4 To 1 cm depth of the solution in a test-tube, add 1 cm depth of aqueous barium chloride, then, add 2 cm depth of dilute hydrochloric acid. Draw appropriate conclusions as to the identity of the anion in each solution. FB 2 contains the anion ………………………………. . FB 3 contains the anion ………………………………. . FB 4 contains the anion ………………………………. . [3]

10 9701/32/O/N/09 © UCLES 2009 For Examiner’s Use (e) Explain why aqueous barium chloride must be added before hydrochloric acid when distinguishing between a sulfite and a sulfate. … … … … [1] (f) Carry out the following test with the solution of FB 2 prepared in (d). test observation To 1 cm depth of the solution of FB 2 in a test-tube add 1 cm depth of aqueous potassium iodide, then add a few drops of starch solution. What is the nature of the reaction taking place between FB 2 and potassium iodide? … … … [2] [Total: 14]

11 9701/32/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.]

12 9701/32/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 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 pale 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 acid) 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) (aq) from orange to green 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.

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 9701/32 Paper 32 (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 32 © UCLES 2009 Question Sections Indicative material Mark 1 (a) PDO Recording Appropriate headings and units Balance readings consistent to 1 dp, to 2 dp or to 3 dp according to precision of balance used Examiner to check subtraction – do not penalise any error here – see section I(d) 1 1 [2] (b) (c) MMO Collection PDO Recording MMO Quality (i) Total volume and temperature recorded for at least 2 different concentrations (ii) Total volume increased by 2.00 cm3 (±0.10 cm3) for at least 3 different concentrations of solution Volumes must be recorded to 2 dp. (iii) Appropriate headings and units (iv) All temperatures recorded to 0.5 oC. Check mass of FB 1 on Supervisor and candidate scripts, particularly if Supervisor and candidate temperatures differ greatly. Round temperatures to nearest 0.5oC if necessary. Where there are repeated temperature readings, take the average correct to 1 decimal place (do not round). (v) & (vi) . Compare temperature at 14.00 cm3 with temperature recorded by the Supervisor. Award (v) & (vi) if within 2.5 oC Award (vi) only if temperature difference is > 2.5 oC and ≤ 5 oC (vii) & (viii) Compare temperature at 16.00 cm3 with temperature recorded by the Supervisor. Award (vii) & (viii) if within 2.5 oC Award (viii) only if temperature difference is > 2.5 oC and ≤ 5 oC 1 1 1 1 2 2 [8] Acceptable form of units – illustrated for mass. 1. using the solidus. / g 2. using brackets. (g) 3. fully in words. mass of ………. in grams 4. composite. mass of ………. in g Where the unit is not incorporated into the heading it must appear after every data entry.

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 32 © UCLES 2009 Question Sections Indicative material Mark (d) ACE Interpretation PDO Display Examiner to check solubility calculated for each volume of water. Use candidate’s mass of FB 1 from (a). Correct rounding required for sig fig displayed. Give 2 marks if all four solubilities are correct. Give 1 of these 2 marks if three only are correct. Deduct 1 mark from those to be awarded if 1. there is an error in subtraction in (a). OR 2. the mass recorded in (a) is less than 10 g or more than 30 g. No negative marks. 3 or 4 significant figures given in each answer given by the candidate 2 1 [3] (e) PDO Layout ACE Interpretation Plots solubility on y-axis and temperature on x-axis. Axes labelled (ignore incorrect or absent units) and points plotted over ½ of each axis - (count large squares containing the points). Consider 1. Spread of the 4 experimental points alone or 2. Spread of the 4 experimental points and 42.5oC even if it is not possible to plot the point at 42.5 oC on the y-axis Scales used are easy for examiner to use and enable all points to be plotted 4 oC/large square is acceptable. Penalise non-linear scales here. Correctly plots all solubility/temperature points. Plotting to within ¼ small square – in the correct square. Attempts to draw a straight line or curve through plotted points (minimum of 3 points) Plots appropriate curve through a minimum of 4 points. This is a mark for the quality of the line drawn and should be a close match to the plotted points. Look for: (i) good spread of points; (ii) even distribution of points either side of the line (3 on line, 1 off, OK); (iii) smooth curve or regular straight line The solubility of FB 1 at 42.5 oC (± ¼ square) read from the graph. Correct solubility recorded or correct solubility rounded to nearest gram recorded 1 1 1 1 1 1 [6] (f) ACE Conclusions Give 1 mark for stating there is a higher solubility at higher temperature 1 [1] Allow these marks if candidate tabulates solubility and, volume of water instead of temperature. If candidate plots solubility against volume of water the following marks only may be awarded: L5 L6 L3 The maximum for the section is 3 marks.

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 32 © UCLES 2009 Question Sections Indicative material Mark (g) ACE Conclusions States that process is endothermic. Uses knowledge of equilibria to explain why it is endothermic. e.g. Refers to absorption of heat energy to dissolve potassium nitrate or States that a rise in temperature shifts equilibrium to the right. (or words to that effect). Beware answers that simply repeat information given in (f). 1 1 [2] (h) ACE Interpretation Give 1 mark for each acceptable source of inaccuracy. Evaporation of water; Supercooling; Thermal time lag in thermometer; Difficulty in seeing crystals form; Time delay in seeing crystals and reading thermometer; Some solid forms on side of tube – not initial FB 1; Precision of thermometer; not human error 2 [2] (i) ACE Improvement PDO Display Outlines steps necessary to determine solubility, (weigh solution, evaporate, weigh residue) Shows working for calculating the solubility. 100 x solid) of mass - solution of (mass solid of mass or 100 x water of mass solid of mass 1 1 [2] Qn 1 Total [26]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 32 © UCLES 2009 Question Sections Indicative material Mark FB 2 is Fe2(SO4)3(s); FB 3 is ZnO(s)/Na2SO3(s); FB 4 is CaSO3(s) [Na2SO3] 2 (a) MMO Collection MMO Decisions Observes: colourless solution with FB 4, yellow, orange or brown solution with FB 2. Describes one of the following gas tests: (i) Potassium dichromate(VI) used in testing for SO2 with FB 3 or FB 4. (orange to green in colour); (ii) Blue litmus turning red on warming with hydrochloric acid; (iii) Limewater used to test gas – no change in the limewater. 1 1 [2] (b) PDO Recording MMO Collection ACE Conclusions (i) All observations in a single table. There must be no repetition of “headings”. (ii) Reports addition of reagents to excess whenever a precipitate is formed on first addition of the reagent. (iii) and (iv) Give 2 marks for correct observations for all 3 cations with both reagents Give 1 of these 2 marks for 2 of the three observations correct. FB 2 – red brown or brown ppt (insol in excess not required but con if either ppt is soluble in excess) with both reagents FB 3 – white ppt soluble in excess with both reagents FB 4 – no ppt with either reagent. (v) Give one mark for conclusions that match observations. minimium observation required FB 2 – Fe3+; red-brown/brown colour of each precipitate FB 3 – Zn2+; white ppt with each reagent and ppt with NH3 soluble in excess of aqueous ammonia FB 4 – two of Ba2+ or Ca2+ or NH4 + from no ppt with either reagent If conclusions fit observations for more than one pair of ions – allow this mark. 1 1 2 1 [5] (c) MMO Decisions Selects appropriate reagent to distinguish between any pair of cations identified in (b). For Ba2+/Ca2+ – accept H2SO4 or chromate/dichromate; For Ba2+/NH4 + – accept H2SO4 or chromate/dichromate or gas turns red litmus blue with NaOH (warming not required); For Ca2+/NH4 + – accept gas turns red litmus blue with NaOH (warming not required) 1 [1]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9701 32 © UCLES 2009 Question Sections Indicative material Mark (d) MMO Collection ACE Conclusion Observes white ppt with BaCl2, soluble in HCl with FB 3 and FB 4. Observes white; off-white or cream (but not yellow) ppt with BaCl2, and FB 2 and ppt insoluble on adding acid (ignore any colour change in the precipitate) Conclusion matching observations. Expected ions - sulfate in FB 2, sulfite in FB 3 and FB 4. Formulae must be correct. 1 1 1 [3] (e) ACE Conclusion Explains that BaCl2 must be added first to form the precipitate (whose solubility is then tested with acid) or Addition of BaCl2 to acidified solution will give no ppt even if sulfite present. Allow wtte. 1 [1] (f) MMO Collection ACE Conclusion Observes one of the following when aqueous potassium iodide is added to the solution of FB 2. A darker solution than in (a) if there is no reference to colour change; Acceptable solution colours are in the range: yellow, orange, red-brown, brown (but not red). accept red-brown or brown solution formed; accept grey or black precipitate AND blue, blue-black, black, purple colour (solution or solid) when starch is added. Identifies FB 2 as an oxidant/oxidising agent or iodide as a reductant/reducing agent or converse.. or states that it is a redox reaction. This mark can be given from either observation. 1 1 [2] Qn 2 Total [14]