Cambridge A Level Chemistry 9701 — 2016 May/June Paper 2 · Variant 3

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 9701/23 Paper 2 AS Level Structured Questions May/June 2016 1 hour 15 minutes Candidates answer on the Question Paper. Additional Materials: Data Booklet Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level This document consists of 9 printed pages and 3 blank pages. [Turn over IB16 06_9701_23/5RP © UCLES 2016 *3280296283*

2 9701/23/M/J/16 © UCLES 2016 Answer all the questions in the spaces provided. 1 An experiment was carried out to determine the percentage of iron in a sample of iron wire. (a) A 3.35 g piece of the wire was reacted with dilute sulfuric acid, in the absence of air, so that all of the iron atoms were converted to iron(II) ions. The resulting solution was made up to 250 cm3. (i) Write a balanced equation for the reaction between the iron in the wire and the sulfuric acid. … [1] A 25.0 cm3 sample of this solution was acidified and titrated with 0.0250 mol dm–3 potassium dichromate(VI). 32.0 cm3 of the potassium dichromate(VI) solution was required for complete reaction with the iron(II) ions in the sample. The relevant half-equations are shown. Cr2O7 2– + 14H+ + 6e– → 2Cr3+ + 7H2O Fe2+ → Fe3+ + e– (ii) Use the half-equations to write an equation for the reaction between the iron(II) ions and the acidified dichromate(VI) ions. … [1] (iii) Calculate the amount, in moles, of dichromate(VI) ions used in the titration. amount = … mol [1] (iv) Calculate the amount, in moles, of iron(II) ions in the 25.0 cm3 sample of solution. amount = … mol [1] (v) Calculate the amount, in moles, of iron in the 3.35 g piece of wire. amount = … mol [1] (vi) Calculate the mass of iron in the 3.35 g piece of wire. mass = … g [1]

3 9701/23/M/J/16 © UCLES 2016 [Turn over (vii) Calculate the percentage of iron in the iron wire. percentage = … % [1] (b) Some electronegativity values are shown. element electronegativity aluminium 1.5 chlorine 3.0 iron 1.8 (i) Use the data to suggest the nature of the bonding in iron(III) chloride. Explain your answer. … … … [2] (ii) Suggest an equation for the reaction between iron(III) chloride and water. … [1] [Total: 10]

4 9701/23/M/J/16 © UCLES 2016 2 Ammonium nitrate is an important fertiliser made by the acid-base reaction between ammonia and nitric acid. (a) Write an equation for the production of ammonium nitrate from ammonia and nitric acid. … [1] The ammonia for this reaction is produced by the Haber process and the nitric acid is produced by oxidation of ammonia. (b) The Haber process involves a reaction between nitrogen and hydrogen at a temperature of 450 °C and a pressure of 20 000 kPa. At a higher reaction temperature, the rate of production of ammonia would be greater. N2(g) + 3H2(g) 2NH3 ∆H = –92 kJ mol–1 The Boltzmann distribution curve shows the distribution of energies in a mixture of nitrogen and hydrogen at 450 °C. number of molecules energy Ea (i) Sketch a second line onto the axes above to show the distribution of energies in the same mixture of gases at a higher temperature. [2] (ii) With reference to the two curves, explain why the rate of production of ammonia would be greater at a higher temperature. … … … [2] (iii) Add a suitable label to the horizontal axis above and use it to explain why a catalyst is used in the Haber process. … … … [2]

5 9701/23/M/J/16 © UCLES 2016 [Turn over (iv) Explain why a higher temperature is not used despite the fact that it would increase the rate of production of ammonia. … … … [2] (c) The first stage in the production of nitric acid involves the reaction of ammonia with oxygen to form nitrogen monoxide, NO, and water. Suggest an equation for this reaction and use oxidation numbers to show that it is a redox reaction. … … … … [3] (d) (i) Draw a dot-and-cross diagram of the ammonium ion. Show the outer electrons only. Use the following code for your electrons. • electrons from nitrogen × electrons from hydrogen [2] (ii) State the shape of an ammonium ion and give the H–N–H bond angle. shape … bond angle … [2] (e) State and explain the problems that arise from the overuse of ammonium nitrate fertiliser when the excess is washed into rivers. … … … … [3] [Total: 19]

6 9701/23/M/J/16 © UCLES 2016 3 Crude oil is a mixture of hydrocarbons and provides many useful chemicals when processed. Two of the stages involved in the processing of crude oil are fractional distillation and cracking. (a) The diagram is a simplified representation of a fractional distillation column. crude oil in fraction A fraction B fraction C fraction D fraction E fraction F (i) What has to be done to the crude oil before it enters the column? … [1] (ii) What trend in structure is there from fraction A to fraction F? … … [1] (iii) State the trends in two properties of the fractions from A to F. … … … [2] (b) The naphtha fraction from fractional distillation of crude oil is used as a starting material for cracking. (i) Write an equation for the cracking of C12H26 to form the products ethene and one other hydrocarbon in a 2 : 1 mole ratio. … [1]

7 9701/23/M/J/16 © UCLES 2016 [Turn over (ii) Suggest a use for each of the products from your equation in (i). Explain what makes each product from (i) suitable for the use you suggest. use of ethene … … explanation … … use of other product … … explanation … … [4] (c) Burning hydrocarbons can cause a number of environmental problems. The products of internal combustion engines can include oxides of nitrogen and oxides of carbon. Sulfur dioxide is a by-product of burning coal in power stations. (i) Explain how and why oxides of nitrogen are produced in internal combustion engines. … … … [2] (ii) Write an equation for the reaction between nitrogen monoxide and carbon monoxide in a catalytic converter. … [1] (iii) Write equations to show the involvement of nitrogen monoxide in the formation of acid rain from atmospheric sulfur dioxide. … … … [3] (iv) Describe two of the problems associated with acid rain. … … … [2] [Total: 17]

8 9701/23/M/J/16 © UCLES 2016 4 Acetoin, CH3COCH(OH)CH3, and diacetyl, CH3COCOCH3, are two of the compounds that give butter its characteristic flavour. Their skeletal formulae are shown. O HO acetoin O O diacetyl (a) Give the systematic name for acetoin. … [1] (b) Identify the reagents and conditions necessary for the conversion of acetoin into diacetyl. … … [2] (c) The infra-red spectrum for acetoin is shown. 100 50 0 transmittance 4000 3000 2000 wavenumber / cm–1 1500 1000 500 (i) Explain the main features of this spectrum, with reference to the peaks with wavenumbers greater than 1500 cm–1. … … … … … [3]

9 9701/23/M/J/16 © UCLES 2016 [Turn over (ii) State and explain how the infra-red spectrum for diacetyl would differ from the infra-red spectrum for acetoin. … … … [2] (d) If a sample of acetoin is reacted with concentrated sulfuric acid, a single product is formed that does not exhibit stereoisomerism. However, if a sample of acetoin is reacted with HBr, a mixture of a pair of stereoisomers is produced. (i) Give the structural formula of the product of the reaction of acetoin with concentrated sulfuric acid. … [1] (ii) Explain why the product in (i) does not exhibit stereoisomerism. … … … [2] (iii) Explain why the product of reaction of acetoin with HBr does exhibit stereoisomerism. … … … [1] (iv) Draw the two stereoisomers from (iii) using the conventional representation. [2] [Total: 14]

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® IGCSE is the registered trademark of Cambridge International Examinations. This document consists of 5 printed pages. © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 9701/23 Paper 2 AS Level Structured Questions May/June 2016 MARK SCHEME Maximum Mark: 60 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 May/June 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 – May/June 2016 9701 23 © Cambridge International Examinations 2016 Question Mark Scheme Mark Total 1 (a) (i) Fe + H2SO4 → FeSO4 + H2 [1] [1] (ii) Cr2O7 2– + 14H+ + 6Fe2+ → 2Cr3+ + 6Fe3+ + 7H2O [1] [1] (iii) (0.025 × 32.0/1000=) 8 × 10–4 [1] [1] (iv) (8 × 10–4 × 6 =) 4.8 × 10–3 [1] [1] (v) (4.8 × 10–3 × 250/25.0=) 4.8 × 10–2 [1] [1] (vi) (4.8 × 10–2 × 55.8=) 2.68 / 2.678 [1] [1] (vii) (2.68/3.35=) 80% [1] [1] (b) (i) covalent small(er) difference in electronegativity between Fe and Cl (than between Al and Cl) [1] [1] [2] (ii) FeCl 3 + 6H2O → [Fe(H2O)6]3+ 3Cl – OR FeCl 3 + 6H2O → [Fe(H2O)6OH]2+ + H+ + 3Cl – [1] [1] [10] 2 (a) NH3 + HNO3 → NH4NO3 [1] [1] (b) (i) line from origin AND below left-hand end of original with peak to right of and lower than original crosses original once AND above right-hand end of original AND above energy axis [1] [1] [2] (ii) (curves show) more molecules with E > Ea (at higher T) so greater frequency of successful (owtte) collisions / more successful (owtte) collisions per unit time [1] [1] [2] (iii) catalysed Ea shown to left of original on horizontal axis so more molecules with E > Ea (in presence of catalyst) [1] [1] [2]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9701 23 © Cambridge International Examinations 2016 Question Mark Scheme Mark Total (iv) production of ammonia is exothermic / (forward) reaction exothermic position of eqm would move to left / reverse / reduce yield (at higher T) [1] [1] [2] (c) 4NH3 + 5O2 → 4NO + 6H2O N changes from –3 to +2 (so oxidation) O changes from 0 to –2 (so reduction) [1] [1] [1] [3] (d) (i) H H H H N+ x x x (+) [1+1] [2] (ii) shape = tetrahedral angle = 109°–109.5° [1] [1] [2] (e) eutrophication / algal bloom / stimulates growth of algae (bacteria) use up oxygen when decomposing the plants / algae block light for plants so less oxygen produced aquatic life / fish die (due to lack of oxygen) [1] [1] [1] [1] [max 3] [19] 3 (a) (i) vaporise / boil / turn to gas [1] [1] (ii) increasing molecular size / no of carbon atoms per molecule / length of carbon chain [1] [1] (iii) increasing b.pt / decreasing volatility increasing viscosity increasing density increasing depth of colour decreasing flammability / decreasing ‘cleanliness’ of flame owtte [1] [1] [2] (b) (i) C12H26 → 2C2H4 + C8H18 [1] [1]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9701 23 © Cambridge International Examinations 2016 Question Mark Scheme Mark Total (ii) ethene use = making polythene / plastic / polymers feature of ethene = double bond / unsaturated octane / alkane use = fuel / petrol feature of octane / alkane = flammability / releases energy when burned / combusted [1] [1] [1] [1] [4] (c) (i) (produced by) reaction of (atmospheric) oxygen and nitrogen due to high temperature / engine provides energy / combustion provides energy [1] [1] [2] (ii) 2NO + 2CO → N2 + 2CO2 / NO + CO → 1 2 N2 + CO2 [1] [1] (iii) NO + 1 2 O2 → NO2 NO2 + SO2 → SO3 + NO SO3 + H2O → H2SO4 / 2H+ + SO4 2– / H+ + HSO4 – [1] [1] [1] [3] (iv) lowers pH of rivers / lakes / kills fish leaches (toxic) aluminium from soil (into rivers / lakes) leaches away soil nutrients damage to buildings / statues / trees / plants / crops ocean acidification / damage to coral [1] [1] [1] [1] [1] [max 2] [17] 4 (a) 3-hydroxybutan(-2-)one [1] [1] (b) H2 / Cr2O7 2– or names heat / reflux / warm [1] [1] [2] (c) (i) absorption at 1670–1740 C (=) O absorption at 2850–3000 C (-) H absorption at 3200–3650 O (-) H [1] [1] [1] [3]

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2016 9701 23 © Cambridge International Examinations 2016 Question Mark Scheme Mark Total (ii) no absorption at 3200–3650 O-H disappears / no O-H bond in diacetyl [1] [1] [2] (d) (i) CH3COCH(=)CH2 [1] [1] (ii) one of the double-bonded C atoms / first C has 2H atoms attached ora so no cis-trans / E-Z / geometric(al) isomerism possible OR no chiral C so mirror images superimposable / molecule not asymmetric [1] [1] [2] (iii) asymmetric / chiral C atom / carbon with four different groups / atoms attached [1] [1] (iv) C H C Br CH3 CH3 O C H C Br C H3 C H3 O [1+1] [2] [14]