Cambridge A Level Chemistry 9701 — 2016 Oct/Nov Paper 3 · Variant 6

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 an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. 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. A copy of the Periodic Table is printed on page 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 9701/36 Paper 3 Advanced Practical Skills 2 October/November 2016 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level This document consists of 12 printed pages. [Turn over IB16 11_9701_36/3RP © UCLES 2016 *1750989411* Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/36/O/N/16 © UCLES 2016 1 Zinc metal is extracted from ores that, in addition to compounds of zinc, can also contain copper and silver. This means zinc metal is often impure. You will investigate the percentage purity of a sample of zinc by reacting it with excess aqueous copper(II) sulfate and comparing the enthalpy change of the displacement reaction with the accepted value. Zn(s) + CuSO4(aq) → Cu(s) + ZnSO4(aq) FB 1 is 1.00 mol dm–3 copper(II) sulfate, CuSO4. FB 2 is powdered impure zinc, Zn. (a) Method Read the whole method before starting any practical work. • Weigh the container with FB 2 and record the mass in the space below. • Support the plastic cup in the 250 cm3 beaker. • Use the measuring cylinder to transfer 25 cm3 of FB 1 into the plastic cup. • Place the thermometer in the solution and record the initial temperature in a suitable 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 (t = 0). • Start timing and do not stop the clock until the whole experiment has been completed at t = 8 minutes. • Measure and record the temperature of the FB 1 in the cup every half minute up to and including t = 2 minutes. • At t = 2 2 1 minutes add all the FB 2 into the cup and stir the contents until t is nearly 3 minutes. • Measure and record the temperature of the mixture in the cup every half minute from t = 3 minutes until t = 8 minutes. Stir occasionally throughout this time. • Weigh the container and any residual FB 2. Record this mass and calculate the mass of FB 2 added. Results Mass Temperature [4] I II III IV

3 9701/36/O/N/16 © UCLES 2016 [Turn over (b) Plot a graph of temperature on the y-axis against time on the x-axis on the grid below. The scale for temperature should extend 3 °C above your highest recorded temperature. You will use the graph to determine the theoretical maximum temperature rise at t = 2 2 1 minutes. Draw two lines of best fit through the points on your graph, the first for the temperature before adding FB 2 and the second for the temperature of the mixture after addition of FB 2. Extrapolate the lines to t = 2 2 1 minutes and determine the theoretical maximum temperature rise, ∆T. theoretical maximum temperature rise at t = 2 2 1 minutes, ∆T = … °C [4] I II III IV

4 9701/36/O/N/16 © UCLES 2016 (c) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Use your answer to (b) to calculate the heat energy, in J, given out when FB 2 was added to the FB 1 in the cup. (Assume that 4.2 J of heat energy raises the temperature of 1.0 cm3 of the mixture by 1.0 °C.) heat energy given out = … J (ii) Use your answer to (i) and the Periodic Table on page 12 to calculate the enthalpy change, in kJ mol–1, for the displacement reaction. Zn(s) + CuSO4(aq) → Cu(s) + ZnSO4(aq) You should assume that FB 2 was pure zinc for this calculation. enthalpy change, ∆H = … … kJ mol–1 (sign) (value) [3] (d) The accepted value for the enthalpy change of this reaction is –217 kJ mol–1. Assuming no heat loss and that the other metals present in FB 2 do not react with aqueous copper(II) sulfate, calculate the percentage of zinc present in FB 2. percentage of Zn = … % [1] (e) A student carried out the same experiment but used pieces of zinc instead of zinc powder. All quantities and the initial temperature of the aqueous copper(II) sulfate remained the same. State and explain what effects this change would have on the graph plotted. … … … … [2] [Total: 14]

5 9701/36/O/N/16 © UCLES 2016 [Turn over 2 Solid hydrated copper(II) sulfate has the formula CuSO4.xH2O where x is the number of moles of water of crystallisation present in 1 mole of compound. You will determine the equation for the reaction that occurs when hydrated copper(II) sulfate is heated to remove the water of crystallisation producing anhydrous copper(II) sulfate. FB 3 is hydrated copper(II) sulfate CuSO4.xH2O. (a) Method Record all masses in the space below. • Weigh the crucible and add 2.2–2.4 g of FB 3. • Weigh the crucible plus FB 3. • Place the crucible on the pipe-clay triangle and heat it gently for approximately 4 minutes. • Leave the crucible to cool and reweigh the crucible plus residue. Keep the crucible and residue for test (c). [4] (b) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the mass of anhydrous copper(II) sulfate, CuSO4, produced after heating. mass of CuSO4 = … g (ii) Calculate the mass of water lost by heating. mass of water = … g I II III IV

6 9701/36/O/N/16 © UCLES 2016 (iii) Use your answers to (i) and (ii) and the Periodic Table on page 12 to deduce the value of x in the formula CuSO4.xH2O. x is … (iv) Use your answer to (iii) to complete the equation for the reaction that occurs when hydrated copper(II) sulfate is heated. You should include state symbols. CuSO4…H2O(…) → CuSO4(…) + …H2O(…) [4] (c) Place the cooled crucible, with the residue, on a heatproof mat and carefully add a few drops of water. (i) Note your observations. … … (ii) Explain your observations in (i) in terms of the reaction occurring. … … … [3] (d) Two students carried out the experiment in (a) and obtained values for x that did not agree with the accepted value. One student calculated a value that was less than the accepted value and the other student calculated a value that was more than the accepted value. In each case, suggest a reason for the error and an improvement that could be made to minimise it. You can assume that the calculations were correctly carried out. Value less than accepted value error … improvement … Value more than accepted value error … improvement … [2] [Total: 13]

7 9701/36/O/N/16 © UCLES 2016 [Turn over 3 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 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. 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. (a) FB 4 and FB 5 are aqueous solutions of equal concentrations, in mol dm–3. Each contains one anion and one cation. The cation is the same in both FB 4 and FB 5. Half fill the 250 cm3 beaker with water. Heat the water to about 80 °C and then turn off the Bunsen burner. This is the hot water bath needed in the tests below. To about a 2 cm depth of aqueous silver nitrate in a test-tube, add a few drops of aqueous sodium hydroxide to give a grey / brown precipitate. Then add aqueous ammonia dropwise until the precipitate just disappears. This solution is Tollens’ reagent and is needed in a test below. (i) Carry out the tests on separate samples of FB 4 and FB 5 and complete the table. test observations FB 4 FB 5 To a 1 cm depth of solution in a test-tube in a test-tube rack, add a spatula measure of sodium carbonate. To a 1 cm depth of solution in a test-tube, add a few drops of acidified potassium manganate(VII). Place the test-tube in the hot water bath. To a 1 cm depth of Tollens’ reagent in a test-tube, add a few drops of solution. Place the test-tube in the hot water bath and leave for several minutes.

8 9701/36/O/N/16 © UCLES 2016 (ii) From your observations in (i), identify the cation present in both FB 4 and FB 5. cation … (iii) From your observations in (i), what can be deduced about the anion present in FB 4? … (iv) Place a 1 cm depth of FB 4 and FB 5 separately in two test-tubes. Measure and record the temperature of the two solutions. FB 4 … °C FB 5 … °C To each solution, add an approximately 2 cm length of magnesium ribbon. Measure and record the maximum temperature reached in each test-tube. FB 4 + Mg … °C FB 5 + Mg … °C (v) Explain why there is a difference in the temperature rise for the reactions of magnesium with solutions FB 4 and FB 5. … … … [8]

9 9701/36/O/N/16 © UCLES 2016 [Turn over (b) FB 6 is a solid that contains two cations from those listed on page 10. You are to plan a series of experiments that will enable you to identify the cations present. You should then carry out your plan, record all the observations you made in a suitable table and identify the cations present. cations present are … and … [5] [Total: 13]

10 9701/36/O/N/16 © UCLES 2016 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 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 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

11 9701/36/O/N/16 © UCLES 2016 2 Reactions of anions ion reaction carbonate, CO3 2– CO2 liberated by dilute acids chloride, Cl –(aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)) bromide, Br –(aq) gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq)) iodide, I –(aq) gives yellow ppt. with Ag+(aq) (insoluble in NH3(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 acids) sulfite, SO3 2–(aq) 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

12 9701/36/O/N/16 © UCLES 2016 To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. Group The Periodic Table of Elements 1 H hydrogen 1.0 2 He helium 4.0 1 2 13 14 15 16 17 18 3 4 5 6 7 8 9 10 11 12 3 Li lithium 6.9 4 Be beryllium 9.0 atomic number atomic symbol Key name relative atomic mass 11 Na sodium 23.0 12 Mg magnesium 24.3 19 K potassium 39.1 20 Ca calcium 40.1 37 Rb rubidium 85.5 38 Sr strontium 87.6 55 Cs caesium 132.9 56 Ba barium 137.3 87 Fr francium – 88 Ra radium – 5 B boron 10.8 13 Al aluminium 27.0 31 Ga gallium 69.7 49 In indium 114.8 81 Tl thallium 204.4 6 C carbon 12.0 14 Si silicon 28.1 32 Ge germanium 72.6 50 Sn tin 118.7 82 Pb lead 207.2 22 Ti titanium 47.9 40 Zr zirconium 91.2 72 Hf hafnium 178.5 104 Rf rutherfordium – 23 V vanadium 50.9 41 Nb niobium 92.9 73 Ta tantalum 180.9 105 Db dubnium – 24 Cr chromium 52.0 42 Mo molybdenum 95.9 74 W tungsten 183.8 106 Sg seaborgium – 25 Mn manganese 54.9 43 Tc technetium – 75 Re rhenium 186.2 107 Bh bohrium – 26 Fe iron 55.8 44 Ru ruthenium 101.1 76 Os osmium 190.2 108 Hs hassium – 27 Co cobalt 58.9 45 Rh rhodium 102.9 77 Ir iridium 192.2 109 Mt meitnerium – 28 Ni nickel 58.7 46 Pd palladium 106.4 78 Pt platinum 195.1 110 Ds darmstadtium – 29 Cu copper 63.5 47 Ag silver 107.9 79 Au gold 197.0 111 Rg roentgenium – 30 Zn zinc 65.4 48 Cd cadmium 112.4 80 Hg mercury 200.6 112 Cn copernicium – 114 Fl flerovium – 116 Lv livermorium – 7 N nitrogen 14.0 15 P phosphorus 31.0 33 As arsenic 74.9 51 Sb antimony 121.8 83 Bi bismuth 209.0 8 O oxygen 16.0 16 S sulfur 32.1 34 Se selenium 79.0 52 Te tellurium 127.6 84 Po polonium – 9 F fluorine 19.0 17 Cl chlorine 35.5 35 Br bromine 79.9 53 I iodine 126.9 85 At astatine – 10 Ne neon 20.2 18 Ar argon 39.9 36 Kr krypton 83.8 54 Xe xenon 131.3 86 Rn radon – 21 Sc scandium 45.0 39 Y yttrium 88.9 57–71 lanthanoids 89–103 actinoids 57 La lanthanum 138.9 89 Ac lanthanoids actinoids actinium – 58 Ce cerium 140.1 90 Th thorium 232.0 59 Pr praseodymium 140.9 91 Pa protactinium 231.0 60 Nd neodymium 144.4 92 U uranium 238.0 61 Pm promethium – 93 Np neptunium – 62 Sm samarium 150.4 94 Pu plutonium – 63 Eu europium 152.0 95 Am americium – 64 Gd gadolinium 157.3 96 Cm curium – 65 Tb terbium 158.9 97 Bk berkelium – 66 Dy dysprosium 162.5 98 Cf californium – 67 Ho holmium 164.9 99 Es einsteinium – 68 Er erbium 167.3 100 Fm fermium – 69 Tm thulium 168.9 101 Md mendelevium – 70 Yb ytterbium 173.1 102 No nobelium – 71 Lu lutetium 175.0 103 Lr lawrencium –

® IGCSE is the registered trademark of Cambridge International Examinations. This document consists of 8 printed pages. © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 9701/36 Paper 3 Advanced Practical Skills 2 October/November 2016 MARK SCHEME Maximum Mark: 40 Published 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 October/November 2016 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 36 © UCLES 2016 Question Answer Marks 1(a) Three masses and all temperatures recorded in a table with unambiguous headings (no need to include the word mass but do not allow weight, allow t for time) and correctly displayed units: / g, (g), in g (allow time in mins or minutes). 1 Temperatures recorded to 0.5 °C. 1 Examiner checks Supervisor’s and candidate’s subtraction for mass of FB 2. Examiner calculates Supervisor value of ∆T / m to 1 dp and records it at the top of the accuracy grid. (∆T = Tmax – T at 2 minutes) Examiner calculates candidate value of ∆T / m to 1 dp and difference from Supervisor. Supervisor ratio <10 10–20 20> Award III if difference is ± 2.0 ± 3.0 ± 4.0 Award IV if difference is ± 1.0 ± 2.0 ± 3.0 Award III and IV according to above table 1 1 4

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 36 © UCLES 2016 Question Answer Marks 1(b) I Axes clearly labelled (headings or units) and T on y-axis. Uniform scale to use more than half of each axis including 3 °C above the highest recorded temperature. 1 II All points plotted to within half a small square and within the correct small square. (Any point that is supposed to be on a line must be on the line and any point that is supposed to be within a small square must not be on a boundary line. Do not allow large dots unless the centre of the dot is correctly positioned). 1 III Appropriate lines of best fit drawn. AND either a straight line / smooth curve after the max T OR a smooth curve from 3 minutes. 1 IV Lines extrapolated and correct value (within 0.2 °C) of ∆T from graph 1 4 1(c)(i) Correctly calculates energy change = 25 × 4.2 × ∆T from (b) or correctly calculated ∆T from table 1 1(c)(ii) Correctly uses value of energy change ∆H = 65.4 correct mass from 1000 × × (c)(i) (a) Negative sign and both answers recorded to 2–4 sf 1 1 3 1(d) Correctly uses = 100 217 × (c)(ii) 1 1

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 36 © UCLES 2016 1(e) effect 1(e) reason maximum T would be to RHS / gradient (to max T) less steep / longer time to the maximum T surface area less (so reaction slower) max T remains same as number of amount / moles (of zinc) is the same max T is smaller as reaction takes longer / is slower / surface area is less greater heat loss Question Answer Marks 1(e) stated effect reason (reason must follow effect) 1 1 2 Total 14

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 36 © UCLES 2016 Question Answer Marks 2(a) Mass of solid used between 2.20 and 2.40 g 1 Table with correct headings / units • mass of crucible • mass of crucible + FB 3 • mass of crucible + residue / FB 3 after heating Units: / g, (g), in g, in gram(me)s 1 Award III if % mass loss is ⩾ 30 but ⩽ 42 Award III and IV if % mass loss is ⩾33 but ⩽39 1 1 4 2(b)(i) and (ii) Correctly calculates mass of anhydrous salt AND mass of water lost. 1 2(b)(iii) Shows expression: mass water mass anhydrous 18 159.6 ÷ Correctly calculates, including showing working, value of x from (iii) and gives as integer 1 1 2(b)(iv) Equation completed with x from (iii) and state symbols 1 4 2(c)(i) (Solid) turns blue and steam / water vapour given off / temperature rises / heat released / hissing / sizzling (owtte) 1 2(c)(ii) Anhydrous salt returns to hydrated or original formula quoted Reaction is exothermic 1 1 3

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 36 © UCLES 2016 Question Answer Marks 2(d) Value less than accepted value: not all water removed and heat to constant mass Value more than accepted value: (anhydrous) salt decomposes and practical method of limiting temperature / heat very gently / thermostatically controlled oven 1 1 2 Total: 13

Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 36 © UCLES 2016 Question Answer Marks FB 4 is HCOOH(aq); FB 5 is HCl (aq); FB 6 is NH4Cl and ZnSO4(s) 3(a)(i) FB 4 FB 5 Fizz Fizz Gas turns limewater cloudy white / milky / chalky / white ppt. OR Gas turns limewater cloudy white / milky / chalky/ white ppt. (Purple) to / goes colourless / paler No reaction / stays / turns purple Silver / grey / AND black ppt / mirror No reaction / white ppt 1 1 1 1 3(a)(ii) hydrogen (ion) / H+ 1 3(a)(iii) it can be oxidised / contains – CHO group / methanoate ion / HCOO– / is a reducing agent 1 3(a)(iv) and 3(a)(v) FB 4 is a weaker acid than FB 5 / FB 4 is less dissociated than FB 5 (ecf on reverse ∆Ts) Energy is needed to break (O to H) bond so less is released 1 1 8

Page 8 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 36 © UCLES 2016 Question Answer Marks 3(b) Use of NaOH(aq) AND NH3(aq) (as test for metal ions) AND using solution of FB 6 / using FB 6 (aq) Use of NaOH(aq) and with excess and result: white ppt soluble in excess Use of NH3(aq) and with excess and result: white ppt soluble in excess With NaOH(aq) and heat and gas / NH3 that turns litmus blue Cations are zinc / Zn2+ and ammonium / NH4 + 1 1 1 1 1 5 Total: 13