Cambridge A Level Chemistry 9701 — 2016 Oct/Nov Paper 4 · Variant 1

READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. 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. A Data Booklet is provided. 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 9701/41 Paper 4 A Level Structured Questions October/November 2016 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet This document consists of 20 printed pages. [Turn over IB16 11_9701_41/4RP © UCLES 2016 *9664884656* Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level

2 9701/41/O/N/16 © UCLES 2016 Answer all the questions in the spaces provided. 1 Copper is a transition element and has atomic number 29. (a) Complete the electronic configuration for the copper atom and the copper ion in the +2 oxidation state. • copper atom [Ar] … • copper ion in the +2 oxidation state [Ar] … [2] (b) The following equilibrium exists between two complex ions of copper in the +2 oxidation state. [Cu(H2O)6]2+ + 4Cl – [CuCl 4]2– + 6H2O (i) Name the type of reaction occurring here. … [1] (ii) State the colours of these two complex ions. [Cu(H2O)6]2+ … [CuCl 4]2– … [1] (iii) State the shape of the [CuCl 4]2– ion. … [1] (iv) Write the expression for the stability constant, Kstab, for this equilibrium. Kstab = [1] (c) Copper also forms the complex ions [Cu(NH3)2(H2O)4]2+ and [Cu(en)(H2O)4]2+ where en is the bidentate ligand ethane-1,2-diamine, H2NCH2CH2NH2. [Cu(H2O)6]2+ + 2NH3 [Cu(NH3)2(H2O)4]2+ + 2H2O equilibrium 1 [Cu(H2O)6]2+ + en [Cu(en)(H2O)4]2+ + 2H2O equilibrium 2 (i) What is meant by the term bidentate ligand? … … [2]

3 9701/41/O/N/16 © UCLES 2016 [Turn over (ii) The table lists the values of stability constants for these two complexes. stability constant, Kstab [Cu(NH3)2(H2O)4]2+ 7.94 × 107 [Cu(en)(H2O)4]2+ 3.98 × 1010 What do these Kstab values tell us about the relative positions of equilibria 1 and 2? … … [1] (d) Nickel forms the complex ion [Ni(en)3]2+ in which it is surrounded octahedrally by six nitrogen atoms. (i) Name the type of stereoisomerism displayed by [Ni(en)3]2+. … [1] (ii) Draw three-dimensional diagrams to show the two stereoisomers of [Ni(en)3]2+. [3] (e) Ethane-1,2-diamine is a useful reagent in organic chemistry. (i) Explain how the amino groups in ethane-1,2-diamine allow the molecule to act as a Brønsted-Lowry base. … … [2] (ii) Write an equation for the reaction of ethane-1,2-diamine with an excess of hydrochloric acid. … [1]

4 9701/41/O/N/16 © UCLES 2016 (f) (i) Under certain conditions, ethane-1,2-diamine reacts with ethanedioic acid, HO2CCO2H, to form the polymer Z. Draw the structure of this polymer, Z, showing two repeat units. [2] (ii) Name the type of reaction occurring during this polymerisation. … [1] (iii) Polymer Z is an example of a biodegradable polymer. Name a polymer that is non-biodegradable. … [1] [Total: 20]

5 9701/41/O/N/16 © UCLES 2016 [Turn over 2 (a) When copper(II) carbonate is heated strongly, it decomposes in a similar way to Group 2 carbonates. Predict what would be observed when anhydrous copper(II) carbonate is heated. … … [1] (b) Describe and explain how the thermal stability of the Group 2 carbonates varies down the group. … … … … [3] (c) Calcium cyanamide, CaCN2, can be used as a fertiliser. (i) Complete the ‘dot-and-cross’ diagram for the cyanamide ion, CN2 2–. Use the following key for the electrons. • electrons from carbon × electrons from nitrogen □ added electron(s) responsible for the overall negative charge N C N 2– [2] (ii) CaCN2 decomposes readily on contact with water forming an insoluble white solid and ammonia only. Suggest an equation for this reaction. … [2] [Total: 8]

6 9701/41/O/N/16 © UCLES 2016 3 The spontaneity (feasibility) of a chemical reaction depends on the standard Gibbs free energy change, ∆G o. This is related to the standard enthalpy and entropy changes by the equation shown. ∆G o = ∆H o – T∆S o (a) State and explain whether the following processes will lead to an increase or decrease in entropy. (i) the reaction of magnesium with hydrochloric acid entropy change … explanation … [1] (ii) solid potassium chloride dissolving in water entropy change … explanation … [1] (iii) steam condensing to water entropy change … explanation … [1] (b) Magnesium carbonate can be decomposed. MgCO3(s) → MgO(s) + CO2(g) ∆H o = +117 kJ mol–1 Standard entropies are shown in the table. substance MgCO3(s) MgO(s) CO2(g) S o / J mol–1 K–1 +65.7 +26.9 +214 (i) Calculate ∆G o for this reaction at 298 K. Include a relevant sign and give your answer to three significant figures. ∆G o = … kJ mol–1 [3] (ii) Explain, with reference to ∆G o, why this reaction becomes more feasible at higher temperatures. … … [1]

7 9701/41/O/N/16 © UCLES 2016 [Turn over (c) On heating, sodium hydrogencarbonate decomposes into sodium carbonate as shown. 2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g) ∆H o = +130 kJ mol–1 ∆S o = +316 J mol–1 K–1 Calculate the minimum temperature at which this reaction becomes spontaneous (feasible). Show your working. temperature = … K [2] (d) The solubility of Group 2 sulfates decreases down the Group. Explain this trend. … … … … [2] [Total: 11]

8 9701/41/O/N/16 © UCLES 2016 4 (a) Cobalt is a transition element that forms complex ions with oxidation states +2 and +3. Explain what is meant by the term transition element. … … [1] (b) The following scheme shows some reactions of [Co(H2O)6]2+. precipitate A solution of C solution of B [Co(H2O)6]2+ OH–(aq) excess Cl –(aq) excess NH3(aq) (i) State the formula of each of the following. A … B … C … [2] (ii) State the colour of the following solutions. [Co(H2O)6]2+ … solution of B … solution of C … [2] (c) Define the term standard electrode potential. … … … [2]

9 9701/41/O/N/16 © UCLES 2016 [Turn over (d) An electrochemical cell was set up to measure the standard electrode potential, , of a cell made of a Co2+ / Co half-cell and a Fe3+ / Fe2+ half-cell. (i) Complete the table with the substance used to make the electrode in each of these half-cells. half-cell electrode Co2+ / Co Fe3+ / Fe2+ [1] (ii) Write the equation for the overall cell reaction. … [1] (iii) Use the Data Booklet to calculate the . = … V [1] (e) The electrochemical cell in (d) was set up again but this time the concentration of Co2+(aq) was 0.050 mol dm–3. The Nernst equation can be used to calculate the value of an electrode potential at different concentrations. E = E o + (0.059 / z) log [Co2+(aq)] Nernst equation (i) Use the Data Booklet and the Nernst equation to calculate the value of E for the Co2+ / Co half-cell in this experiment. E for Co2+ / Co = … V [1] (ii) Suggest how this change will affect the overall cell potential, Ecell, compared to in (d)(iii). Circle your answer. less positive no change more positive [1] (f) Iron(III) ions can oxidise vanadium metal. Construct an equation for the reaction of an excess of iron(III) ions with vanadium metal. Use of the Data Booklet will be helpful. … [2] [Total: 14]

10 9701/41/O/N/16 © UCLES 2016 5 Compound F contains the elements carbon, hydrogen and oxygen only. All carbon-carbon bonds in F are single bonds. The structure of F was analysed by mass spectrometry and infra-red and NMR spectroscopy. (a) The mass spectrum shows that the m / e value for the M peak is 90. The ratio of the heights of the M and M+1 peaks is 22.1 : 0.7. (i) Use the ratio of the heights of the M and M+1 peaks to calculate the number of carbon atoms in a molecule of F. number of carbon atoms = … [2] (ii) Suggest the molecular formula of F. molecular formula = C H O [1] (b) The infra-red spectrum of F was obtained. Use the Data Booklet and your knowledge of infra-red spectroscopy to identify the type of bond and the functional group responsible for these three absorptions. absorption / cm–1 appearance of the peak type of bond functional group 3350 broad and strong 2680 very broad and strong 1725 strong [2]

11 9701/41/O/N/16 © UCLES 2016 [Turn over (c) F was dissolved in deuterated trichloromethane, CDCl 3, and the proton NMR spectrum of this solution obtained. 9 8 11 12 13 14 10 7 6 5 4 3 2 1 0 δ / ppm (i) Use the Data Booklet and your answer to (a)(ii) to complete Table 1 for the proton NMR spectrum of F. The actual chemical shifts for the four absorptions in F have been added for you. Table 1 δ / ppm type of proton relative peak area 1.4 3.9 4.7 12.9 [4] (ii) Describe and explain the splitting pattern for the absorption at δ = 1.4. … … [1] (iii) F was dissolved in D2O and the proton NMR spectrum of this new solution obtained. Two of the absorptions in Table 1 were not present in this spectrum. Which absorptions were not present? … and … [1] (iv) Suggest the structure of F. [1]

12 9701/41/O/N/16 © UCLES 2016 (d) Molecules of cycloheptadiene, C7H10, consist of a seven-membered ring with two carbon-carbon double bonds. (i) Complete the skeletal formulae of two isomers of cycloheptadiene. P Q [1] The isomers P and Q were analysed using carbon-13 NMR spectroscopy. (ii) Predict the number of peaks that will be seen in the carbon-13 NMR spectra of P and Q. isomer number of peaks P Q [2] [Total: 15]

13 9701/41/O/N/16 © UCLES 2016 [Turn over Question 6 starts on the next page.

14 9701/41/O/N/16 © UCLES 2016 6 Ibuprofen and paracetamol are pain-relief drugs. ibuprofen paracetamol O OH N H O OH (a) Ibuprofen and paracetamol both contain the aryl (benzene) functional group. Name the other functional groups present in each molecule. ibuprofen … paracetamol … [2] (b) Ibuprofen contains a chiral centre and shows stereoisomerism. (i) State what is meant by the term chiral centre. … … [1] (ii) Draw the two stereoisomers of ibuprofen. C C [2]

15 9701/41/O/N/16 © UCLES 2016 [Turn over (c) Draw the structures of the organic products when ibuprofen and paracetamol react separately with LiAl H4. product with ibuprofen product with paracetamol [2] (d) A student carried out some reactions with solutions of ibuprofen and paracetamol using reagents D and E and the following results were obtained. ( means a reaction took place.) reagent ibuprofen paracetamol D   E   (i) Suggest a possible identity for each reagent D and E. D … E … [2] (ii) Give the structure of the organic product formed when reagent D reacted with ibuprofen. product with ibuprofen [1] (iii) Give the structure of the organic product formed when reagent E reacted with paracetamol. product with paracetamol [1]

16 9701/41/O/N/16 © UCLES 2016 (e) One of the steps in the manufacture of ibuprofen is shown. X Y CH3COCl Al Cl 3 O (i) Write an equation for the reaction between CH3COCl and Al Cl 3. … [1] (ii) Complete the mechanism for the conversion of X into Y. Include all necessary curly arrows, any relevant dipoles and charges. X [3] (iii) Name the mechanism in (ii). … [1] [Total: 16]

17 9701/41/O/N/16 © UCLES 2016 [Turn over Question 7 starts on the next page.

18 9701/41/O/N/16 © UCLES 2016 7 (a) Sodium chlorate(I), NaCl O, is the active ingredient in commercial bleach. The concentration of chlorate(I) ions was determined by titration. • 10.0 cm3 of a bleach solution was diluted to 250 cm3 in a volumetric flask using distilled water. • Dilute sulfuric acid and an excess of potassium iodide solution were added to a 25.0 cm3 portion of this solution to liberate iodine. • The resulting solution required 20.80 cm3 of 0.100 mol dm–3 aqueous sodium thiosulfate solution to react with the iodine produced. The titration reactions are shown. Cl O– + 2I– + 2H+ → I2 + Cl – + H2O I2 + 2S2O3 2– → 2I– + S4O6 2– Calculate the concentration, in mol dm–3, of Cl O– ions in the bleach solution. concentration of Cl O– = … mol dm–3 [3] (b) An indicator was used in the thiosulfate-iodine titration. (i) Name a suitable indicator for this titration. … [1] (ii) State the expected colour change you would observe at the end-point in this titration. from … to … [1] (iii) State when in the procedure you would add the indicator. … … [1]

19 9701/41/O/N/16 © UCLES 2016 [Turn over (c) The concentration of chlorate(I) ions can also be determined by adding an excess of hydrogen peroxide to the sample of bleach and measuring the volume of oxygen gas produced. H2O2 + NaCl O → NaCl + O2 + H2O water oxygen gas 100 cm3 measuring cylinder hydrogen peroxide 5.0 cm3 bleach When an excess of aqueous hydrogen peroxide was added to 5.0 cm3 of a different bleach solution, 82 cm3 of oxygen was produced at room temperature and pressure. Calculate the concentration of Cl O– ions in this bleach solution. concentration of Cl O– = … mol dm–3 [2] (d) Trichlorocyanuric acid, C3Cl 3N3O3, acts as a chlorine buffer and disinfectant for swimming pools. It reacts with water to give chloric(I) acid, HCl O. C3Cl 3N3O3 + 3H2O C3H3N3O3 + 3HCl O (i) Write the expression for Kc for this equilibrium. Kc = [1] (ii) In outdoor swimming pools, the HCl O is decomposed by sunlight. The decomposition of HCl O is a redox reaction which forms a gas that relights a glowing splint. Describe and explain the effect of the decomposition of HCl O on the equilibrium in (d). State the effect on Kc. … … effect on Kc … [2]

20 9701/41/O/N/16 © UCLES 2016 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. 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. 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. (iii) The decomposition of HCl O is a redox reaction. Suggest an equation for this reaction. … [1] (e) The buffer solution in blood is a mixture of carbonic acid, H2CO3, and hydrogencarbonate ions, HCO3 –. Healthy blood has a pH of 7.40. H2CO3 + H2O HCO3 – + H3O+ Ka = 7.94 × 10–7 mol dm–3 (i) Explain how this buffer system acts to control the blood pH. Include equations in your answer. … … … … [2] (ii) A patient’s blood has a [HCO3 –] : [H2CO3] ratio of 9.5 : 1. Calculate the pH of the patient’s blood. pH = … [2] [Total: 16]

® IGCSE is the registered trademark of Cambridge International Examinations. This document consists of 17 printed pages. © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 9701/41 Paper 4 A Level Structured Questions October/November 2016 MARK SCHEME Maximum Mark: 100 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 41 © UCLES 2016 Question Answer Mark 1(a) Cu [Ar] 3d104s1 Cu2+ [Ar] 3d9 (4so) 1 1 2 1(b)(i) ligand exchange / replacement / displacement / substitution 1 1 1(b)(ii) [Cu(H2O)6]2+ blue and [CuCl4]2– yellow OR yellow / green OR green / yellow 1 1 1(b)(iii) tetrahedral 1 1 1(b)(iv) Kstab = [CuCl4 2–] / [Cu(H2O)6 2+][Cl–]4 1 1 1(c)(i) a species that contains two lone pairs that (each) form a co-ordinate / dative bond OR are donated (to a metal ion / atom) 1 1 2 1(c)(ii) equilibrium 2 lies more to the RHS / favours forward reaction more 1 1 1(d)(i) optical 1 1 1(d)(ii) 3D correct for octahedral one correct structure with 3D second correct with 3D 1 1 1

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 3 1(e)(i) lone pair receive / accepts a proton / H+ 1 1 2 1(e)(ii) H2NCH2CH2NH2 + 2HCl → ClH3NCH2CH2NH3Cl OR H2NCH2CH2NH2 + 2H+ → H3N+CH2CH2N+H3 1 1 1(f)(i) amide bond, displayed or –CONH– rest of the molecule with continuation bonds O O H N N H O H N O N H 1 1 2 1(f)(ii) condensation / addition – elimination 1 1 1(f)(iii) any named polyalkene / eg polyethene, PVC allow Bakelite or Kevlar 1 1 Total: 20

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 2(a) solid remains 1 1 2(b) stability increases (down the group) as size / radius of (metal) ion / M2+ increases so polarisation / distortion of anion / carbonate ion decreases 1 1 1 3 2(c)(i) 2 2(c)(ii) CaCN2 + 3H2O → CaCO3 + 2NH3 CaCO3 correct equation 1 1 2 Total: 8

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 3(a)(i) (entropy) increases / is positive and H2 / gas is formed 1 1 3(a)(ii) (entropy) increases / is positive and (KCl (aq)) solution has (free) moving / mobile ions / aqueous ions 1 1 3(a)(iii) (entropy) decreases / is negative and decrease in gas 1 1 3(b)(i) ∆So = 26.9 + 214 – 65.7 = (+) 175.2 (J K–1 mol–1) ∆Go = 117 – (298 × 175.2 / 1000) OR ∆Go = 117 000 – (298 × 175.2) ∆Go = + 64.8 (kJ mol–1) 1 1 1 3 3(b)(ii) T∆S is more positive than ∆H / T∆S increases / –T∆S more negative and ∆G is negative / decrease / less positive 1 1 3(c) use of ∆G = 0 or T∆S = 1 ∆H T = 130 / (316 / 1000) = 410 / 411 / 412 / 411.4 (K) 1 1 2

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 3(d) hydration enthalpy and lattice energy both more endothermic / more positive / less exothermic / less negative (down the group) ∆Hhyd decreases more / faster and ∆Hsol becomes (more) endothermic / (more) positive / less exothermic / less negative 1 1 2 Total: 11 Question Answer Mark 4(a) (an element) forming one or more (stable) ions or compounds or oxidation states with partially filled / incomplete d orbitals 1 1 4(b)(i) A Co(OH)2 OR Co(H2O)4(OH)2 B [CoCl4]2– C [Co(NH3)6]2+ OR [Co(NH3)6]3+ two correct = 1 mark three correct = 2 marks 2 4(b)(ii) [Co(H2O)6]2+ pink solution of B blue solution of C brown/yellow/orange

Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark two correct = 1 mark three correct = 2 marks 2

Page 8 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 4(c) (emf / potential / E) of an electrode OR a half-cell compared to / connected to (S)HE which can be called a “hydrogen half-cell” at concentration of 1 mol dm–3 and pressure of 1 atm (or in Pa) OR 298 K 1 1 2 4(d)(i) half-cell electrode Co2+ / Co Co / cobalt Fe3+ / Fe2+ Pt / carbon / graphite 1 1 4(d)(ii) Co + 2Fe3+ → Co2+ + 2Fe2+ 1 1 4(d)(iii) Eo cell = 0.77 – (– 0.28) = (+ or –)1.05 (V) 1 1 4(e)(i) Eelectrode = – 0.28 + (0.059 / 2) log [0.05] = –0.32 / –0.318 (V) 1 1 4(e)(ii) more positive 1 1 4(f) 4Fe3+ + V + H2O → VO2+ + 4Fe2+ + 2H+ VO2+ correct equation 1 1

Page 9 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 2 Total: 14

Page 10 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 5(a)(i) (100 / 22.1) × (0.7 / 1.1) or 100 0.7 22.1 1.1 × × or 2.87 / 2.88 / 2.9 3 carbon atoms 1 1 2 5(a)(ii) C3H6O3 1 1 5(b) absorption / cm–1 appearance of the peak type of bond functional group 3350 broad and strong OH or O–H alcohol / ROH 2680 very broad and strong OH or O–H (carboxylic) acid / CO2H 1725 strong C = O (carboxylic) acid / CO2H 2

Page 11 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 5(c)(i) δ/ppm type of proton relative peak area 1.4 –CH3 or –CH2 or –CH or alkane 3 3.9 –OCH or –OCH2 or –OCH3 or CH or alkyl next to electronegative atom / oxygen 1 4.7 –OH or alcohol 1 12.9 –OH or –CO2H or carboxylic acid 1 4 5(c)(ii) doublet and 1 / one H / proton on neighbouring OR adjacent carbon 1 1 5(c)(iii) 4.7 and 12.9 OR –OH and –CO2H 1 1 5(c)(iv) 1 1 5(d)(i) both required for 1 mark 1 1

Page 12 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 5(d)(ii) isomer number of peaks P 4 Q 4 1 1 2 Total: 15 Question Answer Mark 6(a) ibuprofen: carboxylic acid / carboxyl paracetamol: phenol and amide any two = 1 mark all three = 2 marks 2 6(b)(i) (chiral centre is a) carbon OR atom that has four different groups / atoms / species attached to it 1 1

Page 13 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 6(b)(ii) one correct isomer second diagram shows second isomer 1 1 2 6(c) with ibuprofen with paracetamol 1 1 2

Page 14 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 6(d)(i) (reagent D) Na2CO3 / any carbonate (reagent E) Cl2 / Br2 1 1 2 6(d)(ii) 1 1 6(d)(iii) 1 1 6(e)(i) CH3COCl + AlCl3 → CH3CO+ + AlCl4 – 1 1

Page 15 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 6(e)(ii) curly arrow from ring system to CH3CO+ correct intermediate curly arrow from C–H bond into ring 1 1 1 3 6(e)(iii) electrophilic substitution 1 1 Total: 16

Page 16 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 7(a) moles of thiosulfate = 0.1 × 20.8 / 1000 = 2.08 × 10–3 moles of ClO– in 25 cm3 portion = 2.08 × 10–3 / 2 = 1.04 × 10–3 (moles of ClO– in 250 cm3 = 1.04 × 10–2) concentration of ClO– = 1.04 × 10–2 / (10 / 1000) = 1.04 (mol dm–3) 1 1 1 3 7(b)(i) starch 1 1 7(b)(ii) blue OR black to colourless 1 1 7(b)(iii) towards / close to the end-point of the titration / when the solution goes yellow 1 1 7(c) moles of O2 = 82 / 24 000 = 3.42 × 10–3 = moles ClO– ions concentration of ClO– = 3.42 × 10–3 / (5 / 1000) = 0.68 / 0.683 / 0.684 (mol dm–3) 1 1 2 7(d)(i) Kc = 3 3 3 3 3 3 3 3 3 3 3 2 [C H N O ][HC O ] [C C N O ][H 0] l l 1 1 7(d)(ii) (position of eqm) moves to the right / forward reaction predominates / more HClO made (as [HClO] decreases) no effect on Kc 1 1 2

Page 17 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9701 41 © UCLES 2016 Question Answer Mark 7(d)(iii) 2HClO → 2HCl + O2 OR 2HClO → H2 + Cl2 + O2 1 1 7(e)(i) addition of acid: H+ + HCO3 – → H2CO3 OR H+ + HCO3 – → H2O + CO2 addition of base: OH– + H2CO3 → HCO3 – + H2O OR H+ + OH– → H2O and position of eqm moves to the right OR OH– + HCO3 – → CO3 2– + H2O 1 1 2 7(e)(ii) Ka = ([H+][HCO3 –] / [H2CO3]) [H+] = (7.94 × 10–7) × 1 / 9.5 = 8.36 × 10–8 pH = – log[H+] = 7.08 1 1 2 Total: 16