Cambridge A Level Chemistry 9701 — 2013 May/June Paper 3 · Variant 5

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. Electronic calculators may be used. 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 9701/35 Advanced Practical Skills 1 May/June 2013 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 IB13 06_9701_35/4RP © UCLES 2013 *5493668379* Session Laboratory For Examiner’s Use 1 2 Total

2 9701/35/M/J/13 © UCLES 2013 For Examiner’s Use I II III IV V 1 You will determine the enthalpy change, ∆H, for the reaction of anhydrous magnesium sulfate, MgSO4, with water to form hydrated magnesium sulfate, MgSO4.7H2O. In step 1 you will dissolve a known mass of anhydrous magnesium sulfate in a known volume of water and fi nd the temperature change. In step 2 you will fi nd the temperature change on adding a known mass of hydrated magnesium sulfate to a known volume of water. You will then use your results to calculate the enthalpy change for the reaction. MgSO4(s) + 7H2O(l) → MgSO4.7H2O(s) FA 1 is anhydrous magnesium sulfate, MgSO4. FA 2 is hydrated magnesium sulfate, MgSO4.7H2O. distilled water (a) Method Step 1 MgSO4(s) + aq → MgSO4(aq) ● Place the plastic cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25 cm3 of distilled water into the plastic cup. ● Weigh the container with FA 1 and record the balance reading in a suitable form in the space below. ● Place the thermometer in the water and record the initial temperature in the table of results. Tilt the cup if necessary so that the bulb of the thermometer is fully covered. This is the temperature at time zero. Start timing. ● Record the temperature of the water at 1 minute and at 2 minutes. ● At 2½ minutes tip all the FA 1 into the water and stir to dissolve. ● Record the temperature of the solution at 3, 4, 5, 6, 7 and 8 minutes. ● Reweigh the container with any residual FA 1 and record the balance reading and the mass of FA 1 used. ● Rinse out the plastic cup and shake it to remove excess water. Results Mass Temperature Time in minutes 0 1 2 3 4 5 6 7 8 Temperature / °C [5]

3 9701/35/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use I II III IV (b) Plot temperature on the y-axis against time on the x-axis on the grid below. You will use the graph to determine the theoretical temperature change at 2½ minutes. Draw two straight lines of best fi t on your graph, one for the temperature of the water before adding FA 1 and the other for the cooling of the solution once the reaction is complete. Extrapolate the two lines to 2½ minutes and determine the change in temperature at this time. temperature change at 2½ minutes = … °C [4]

4 9701/35/M/J/13 © UCLES 2013 For Examiner’s Use (c) Method Step 2 MgSO4.7H2O(s) + aq → MgSO4(aq) ● Read through the method and prepare a suitable table for your results. ● Place the plastic cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25 cm3 of distilled water into the plastic cup. ● Weigh the container with FA 2 and record the balance reading below. ● Place the thermometer in the water and record the initial temperature. Tilt the cup if necessary so that the bulb of the thermometer is fully covered. ● Tip all the FA 2 into the water and stir to dissolve. ● Record the lowest temperature. ● Reweigh the container with any residual FA 2 and record the balance reading and the mass of FA 2 used. Results [3] I II III

5 9701/35/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use (d) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Using your answer to (b), calculate the heat energy produced when FA 1 was added to water in step 1. (Assume that 4.3 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 °C.) heat energy produced = … J (ii) Calculate the enthalpy change, in kJ mol–1, when 1 mole of FA 1, MgSO4, is dissolved. (Ar: O, 16.0; Mg, 24.3; S, 32.1) enthalpy change = … … kJ mol–1 (sign) (value) (iii) Using your results from (c), calculate the heat energy absorbed when FA 2 was added to water in step 2. (Assume that 4.3 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 °C.) heat energy absorbed = … J (iv) Calculate the enthalpy change, in kJ mol–1, when 1 mole of FA 2, MgSO4.7H2O, is dissolved. (Ar: H, 1.0; O, 16.0; Mg, 24.3; S, 32.1) enthalpy change = … … kJ mol–1 (sign) (value) (v) Use your answers to parts (ii) and (iv) and the equations for the reactions shown in steps 1 and 2 to determine the enthalpy change, in kJ mol–1, for the reaction below. MgSO4(s) + 7H2O(l) → MgSO4.7H2O(s) enthalpy change, ∆H = … … kJ mol–1 (sign) (value) [6] I II III IV V VI

6 9701/35/M/J/13 © UCLES 2013 For Examiner’s Use (e) (i) Complete the following table. The maximum error in a single thermometer reading is … °C. The maximum error in measuring the change in temperature in step 2 is … °C. (ii) Calculate the maximum percentage error in the temperature change in step 2. maximum percentage error in the temperature change in step 2 = … % [2] (f) (i) A student suggested that the experiment could be made more accurate by using 50 cm3 of water in step 1 and step 2. State whether the student is correct or incorrect and justify your answer. The student is … because … … . [1] (ii) Another student carried out step 2 twice for a different hydrated salt and obtained the following results. First result: mass used = 3.34 g; drop in temperature = 4.0 °C Second result: mass used = 4.18 g; drop in temperature = 5.0 °C The student then used the mean mass and mean temperature drop when calculating the enthalpy change for the reaction. Explain whether or not the student was justifi ed in using the results in this way, by showing appropriate calculations. … … … … [2] [Total: 23]

7 9701/35/M/J/13 © UCLES 2013 [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 name or correct formula of the element or compound must be given. FA 3, FA 4 and FA 5 are aqueous solutions of salts. Read through the tests before starting the practical work. (a) Many cations are identifi ed by using aqueous sodium hydroxide and aqueous ammonia in small amounts and then to excess. Carry out the following tests and record all your observations in the table below. Do not discard the fi nal products in these tests as you will need to use them in part (b). test observations FA 3 FA 4 FA 5 (i) To 1 cm depth of solution in a test-tube, add aqueous sodium hydroxide, until in excess. (do not discard) (ii) To 1 cm depth of solution in a test-tube, add aqueous ammonia, until in excess. (do not discard) [3]

8 9701/35/M/J/13 © UCLES 2013 For Examiner’s Use (b) At least one of the solutions contains a second cation, the ammonium ion, NH4 +. Devise a test to identify which salt or salts contain the ammonium ion. You are to use the products of the reactions in (a) when carrying out your test. (i) Which of the following sets of products will you use in your test? Tick the appropriate box. ● products with excess aqueous sodium hydroxide ● products with excess aqueous ammonia (ii) Describe the test and expected observations if NH4 + is present. … … … (iii) Carry out your test and record your observations clearly in the space below. [4]

9 9701/35/M/J/13 © UCLES 2013 [Turn over For Examiner’s Use (c) FA 3, FA 4 and FA 5 each contains a different anion which is sulfate, chloride, or nitrate. Using the Qualitative Analysis Notes on page 11, select reagents to allow you to identify positively which anion is in each salt using the minimum number of tests. Record your reagents and your observations in the table below. Indicate where a test is unnecessary using a dash, —. reagent(s) FA 3 FA 4 FA 5 [5] (d) From your observations in (a), (b) and (c), identify as many ions that could be present as possible. FA 3 FA 4 FA 5 cation(s) anion [5] [Total: 17] I II III IV V I II III IV V

10 9701/35/M/J/13 © UCLES 2013 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 9701/35/M/J/13 © UCLES 2013 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. 9701/35/M/J/13 © UCLES 2013 BLANK PAGE

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2013 series 9701 CHEMISTRY 9701/35 Paper 3 (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 should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 2013 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

Page 2 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 35 © Cambridge International Examinations 2013 Question Sections Indicative material Mark Total 1 (a) MMO Collection I All thermometer readings recorded and two weighings + correct mass of FA 1 recorded. 1 PDO Recording II Correct headings and units in both tables in (a) (Mass) and (c) (Mass and temperature). Must use solidus, brackets or describe unit fully in words. If units not included in column headings every entry must have the correct unit shown. 1 III Temperature recorded to 0.5 ºC (must have at least one at 0.5 ºC and one to 0.0 ºC) and weighings to same number of dp (on page 2). 1 Examiner to calculate Supervisor – candidate ∆T/m (∆T from table). MMO Quality Award IV and V if δ ≤ 0.20 ºC g-1 Award IV if 0.20 < δ ≤ 0.50 ºC g-1 1 1 [5] (b) PDO Layout I Uniform scales chosen to use more than half of each axis. Axes labelled, ignore units. 1 II All points correctly plotted within ½ small square and in correct small square on y-axis and on the line on x-axis. 1 III Appropriate lines of best fit are drawn. 1 ACE Interpretation IV Correct value of ∆T (or to nearest 0.5 ºC) from extrapolated lines (ignore sf). 1 [4] (c) PDO Recording I Table drawn to include weighings, correct mass of FA 2, initial and final thermometer readings. 1 Examiner to calculate Supervisor – candidate ∆T MMO Quality Award II and III if δ ≤ 0.5 ºC Award II only if 0.5 < δ ≤ 1.0 ºC 1 1 [3]

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 35 © Cambridge International Examinations 2013 (d) (i) & (iii) ACE Interpretation I Correctly calculates 25 x 4.3 × ∆T for step 1 and for step 2. 1 (ii) II Correctly calculates
  . 
    (if number of moles calculated, value used must be to at least 2 sf). 1 (iv) III Correctly calculates
  . 
    (do not penalise incorrect sign a second time). 1 (v) IV Correctly calculates ∆H from answers to (ii) and (iv) with correct sign ((ii) – (iv)) (allow ecf for sign) 1 PDO Display V Working in the right direction shown in parts (i) – (iv). (i) and (iii) use of mc∆T; (ii) use of 120.4; (iv) use of 246.4 1 VI All final answers given to 3 or 4 sf (minimum of 3 answers). 1 [6] 1 (e) (i) ACE Interpretation Single thermometer reading ± 0.5 ºC (or ±0.1 ºC if candidate recorded T to 0.1 ºC). ∆T ± 1.0 ºC (or ± 0.2 ºC) 1 (ii) Calculates {1.0/∆T} × 100 (or {0.2/∆T} × 100) for step 2 to 2 or more sf. Allow ecf. 1 [2] (f) (i) ACE Improvements Student incorrect as smaller temp change or % error in temp change increased. 1 [1] (ii) MMO Interpretation MMO Decisions Calculates ∆T/m or m/∆T or Q/m for each result. Allow mass of solid × c × ∆T. Yes, values concordant/consistent (shown:– ∆T/m:1.2/1.20/1.198 and 1.2/1.20/1.196 or m/∆T: 0.84/0.835 and 0.84/0.836 or Q/m: 128.7 and 128.6 respectively). 1 1 [2] [Total: 23]

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 35 © Cambridge International Examinations 2013 FA 3 is CrCl3; FA 4 is (NH4)2Fe(SO4)2; FA 5 is Pb(NO3)2 2 (a) MMO Collection FA 3 gives grey-green ppt soluble in NaOH/ giving dark green solution in excess and grey-green ppt insoluble in excess NH3 1 FA 4 gives green/dirty green ppt insoluble in excess of both and turning brown/darkening in at least one 1 FA 5 gives white ppt soluble in excess NaOH and white ppt insoluble in excess NH3 or Award 1 mark if all NaOH observations, including in excess, are correct. Award 1 mark if all NH3 observations, including in excess, are correct. 1 [3] (b) MMO Decisions Selects products with excess NaOH in (i) and warms the product in (ii). 1 Tests gas/ammonia with (damp) red litmus and turns blue in (ii). (Stand-alone mark irrespective of reagent chosen.) 1 MMO Collection FA 4 gives (gas) turning red litmus blue Neither of the others give a positive result. 1 1 [4] (c) MMO Decisions I Selects any 2 from: AgNO3, BaCl2 or Ba(NO3)2, Pb(NO3)2 (full reagent names or formulae needed) 1 II NaOH + Al and warm do not penalise OH– + Al and warm if full names not given above 1 MMO Collection III and IV Any 2 of: only FA 3 gives (white) ppt with Ag+; only FA 4 gives white ppt with Ba2+ (allow off- white); FA 3 and FA 4 give white ppt with Pb2+ 2 V FA 5 and FA 4 (if tested) form gas/ammonia on warming (or warm in reagent column) which turns (damp) red litmus paper blue 1 [5]

Page 5 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2013 9701 35 © Cambridge International Examinations 2013 (d) ACE Conclusions I FA 3 contains Cr3+ and Cl– 1 II FA 4 contains Fe2+ and SO4 2– 1 III Only FA 4 contains NH4 + 1 IV FA 5 contains either Pb2+ or Al3+ (both given) 1 V Only FA 5 contains NO3 – 1 [5] [Total: 17]