Cambridge A Level Chemistry 9701 — 2015 May/June Paper 2 · Variant 2

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 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. 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 9701/22 Paper 2 Structured Questions AS Core May/June 2015 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 8 printed pages. [Turn over IB15 06_9701_22/4RP © UCLES 2015 *0728412024*

2 9701/22/M/J/15 © UCLES 2015 Answer all the questions in the spaces provided. 1 (a) Chemists recognise that atoms are made of three types of particle. Complete the following table with their names and properties. name of particle relative mass relative charge +1 1/1836 [3] (b) Most elements exist naturally as a mixture of isotopes, each with their own relative isotopic mass. The mass spectrum of an element reveals the abundances of these isotopes, which can be used to calculate the relative atomic mass of the element. Magnesium has three stable isotopes. Information about two of these isotopes is given. isotope relative isotopic mass percentage abundance 24Mg 24.0 79.0 26Mg 26.0 11.0 (i) Defi ne the term relative isotopic mass. … … … [2] (ii) The relative atomic mass of magnesium is 24.3. Calculate the percentage abundance and hence the relative isotopic mass of the third isotope of magnesium. Give your answer to three signifi cant fi gures percentage abundance = … isotopic mass = … [3]

3 9701/22/M/J/15 © UCLES 2015 [Turn over (c) Magnesium can be produced by electrolysis of magnesium chloride in a molten mixture of salts. (i) Give equations for the anode and cathode reactions during the electrolysis of molten magnesium chloride, MgCl 2. anode … cathode … [2] The electrolysis is carried out under an atmosphere of hydrogen chloride gas to convert any magnesium oxide impurity into magnesium chloride. (ii) An investigation of the reaction between magnesium oxide and hydrogen chloride gas showed that an intermediate product was formed with the composition by mass Mg, 31.65%; O, 20.84%; H, 1.31% and Cl, 46.20%. Calculate the empirical formula of this intermediate compound. empirical formula … [2] (d) The acid/base behaviour of the oxides in the third period varies across the period. (i) Describe this behaviour and explain it with reference to the structure and bonding of sodium oxide, Na2O, aluminium oxide, Al 2O3, and sulfur trioxide, SO3. … … … [2] (ii) Write equations for reactions of these three oxides with hydrochloric acid and/or sodium hydroxide as appropriate. … … … … [4] [Total: 18]

4 9701/22/M/J/15 © UCLES 2015 2 Sulfuric acid is an important chemical with a variety of uses. It is manufactured by the Contact process, the fi rst stage of which involves the conversion of sulfur or a sulfi de ore, such as galena, PbS, into sulfur dioxide, SO2. (a) (i) Write an equation for the reaction between galena and oxygen to form sulfur dioxide and lead(II) oxide. … [2] (ii) Identify the oxidation number changes that take place during this reaction. … … [2] (b) The second stage of the Contact process involves the production of sulfur trioxide, SO3, from sulfur dioxide. 2SO2(g) + O2(g) 2SO3(g) ∆H = –197 kJ mol–1 (i) State the temperature usually chosen for this conversion and explain this in terms of reaction rates and Le Chatelier’s principle. temperature … explanation … … … … [3] (ii) State and explain the pressure conditions that would give the best rate and best yield of sulfur trioxide. Explain why these conditions are not actually used. … … … … … [3] (c) In the third stage of the process the sulfur trioxide is dissolved in 98% sulfuric acid followed by carefully controlled addition of water. (i) Explain why the sulfur trioxide is not dissolved directly in water to produce sulfuric acid. … … [1]

5 9701/22/M/J/15 © UCLES 2015 [Turn over (ii) Write equations for the reaction of sulfur trioxide with sulfuric acid and for the subsequent reaction with water. … … [2] (d) Explain why sulfur dioxide is used as an additive in some foods and wines. … … … [2] (e) The sulfur dioxide content of wine is most commonly measured by the Ripper Method which involves titration with iodine in the presence of starch as an indicator. SO2(aq) + I2(aq) + 2H2O(l) → 2I –(aq) + SO4 2–(aq) + 4H+(aq) A 50.0 cm3 sample of wine required 12.35 cm3 of 0.010 mol dm–3 I2(aq) for complete reaction with the SO2. (i) How many moles of SO2 are present in 50.0 cm3 of wine? moles of SO2 in 50.0 cm3 = … [1] (ii) How many moles of SO2 are present in 1 dm3 of wine? moles of SO2 in 1 dm3 = … [1] (iii) How many milligrams, mg, of SO2 are present in 1 dm3 of wine? Give your answer to three signifi cant fi gures. (1 g = 1000 mg) mass of SO2 in 1 dm3 = … mg [1] [Total: 18]

6 9701/22/M/J/15 © UCLES 2015 3 Ethane reacts with chlorine to form chloroethane. C2H6(g) + Cl 2(g) → C2H5Cl (g) + HCl (g) (a) (i) Use bond energies from the Data Booklet to calculate the enthalpy change for this reaction. Include a sign in your answer. enthalpy change = … kJ mol–1 [3] (ii) State the conditions needed for this reaction to occur. … [1] (iii) Use a series of equations to describe the mechanism of this reaction including the names of each stage and an indication of how butane can be produced as a minor by-product. … … … … … … [5] (b) Chloroethane can be converted back into ethane by a two-stage process via an intermediate compound, X. C2H5Cl C2H6 X reaction 1 reaction 2 (i) Give the name of X. … [1] (ii) Suggest the reagent and conditions needed for reaction 1. … [2] (iii) Suggest the reagent and conditions needed for reaction 2. … [1] [Total: 13]

7 9701/22/M/J/15 © UCLES 2015 [Turn over 4 There are seven structural isomers with the molecular formula C5H10O that are carbonyl compounds. Four of these are aldehydes. These four aldehydes, A, B, C and D, have the following properties. ● Aldehyde A has a straight chain while B, C and D are branched. ● Aldehyde B is the only one of the four isomers with a chiral centre and it exists as a pair of optical isomers. ● Aldehyde C has two methyl groups in its structure but D has three. (a) (i) Give the structure of each of the four isomers. A B C D [4] (ii) Draw the three-dimensional structures of the two optical isomers of B. [2]

8 9701/22/M/J/15 © UCLES 2015 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. (b) (i) Describe a chemical test that would allow you to distinguish between any of the four isomers A to D and any of the other three structural isomers of C5H10O, that are carbonyl compounds. In your answer you should describe any necessary reagents and conditions as well as explaining what you would see in each case. … … … … … [3] (ii) Describe a test that would give the same result with all seven carbonyl isomers of C5H10O. … … … [2] [Total: 11]

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the May/June 2015 series 9701 CHEMISTRY 9701/22 Paper 2 (Structured Questions AS Core), maximum raw mark 60 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 2015 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 2015 9701 22 © Cambridge International Examinations 2015 Question Mark Scheme Mark Total 1 (a) name of particle relative mass relative charge proton 1 +1 electron 1/1836 –1 neutron 1 0 [1] [1] [1] [3] (b) (i) Mass of an atom(s) relative to 1 / 12th (the mass) of (an atom of) carbon-12 OR relative to carbon-12 which is (exactly) 12 [1] [1] [2] (ii) % of third isotope = 10 24.3 100 10x 11.0) (26 79) (24 = + × + × 10x = 248 x = 24.8 (3s.f.) [1] [1] [1] [3] (c) (i) anode 2Cl –
Cl2 + 2e– cathode Mg2+ + 2e–
Mg [1] [1] [2] (ii) Mg O H Cl 24.3 31.65 16 20.84 1 1.31 35.5 46.2 1.30 1.30 1.31 1.30 = 1:1:1:1 MgOHCl [1] [1] [2] (d) (i) Na2O basic / alkaline; Al2O3 amphoteric / acidic and basic; SO3 acidic Na2O (giant) ionic AND SO3 (simple / molecular) covalent [1] [1] [2] (ii) Na2O + 2HCl
2NaCl + H2O Al2O3 + 6HCl
2AlCl3 + 3H2O Al2O3 + 2NaOH + 7H2O
2NaAl(OH)4(H2O)2 OR Al2O3 + 2NaOH + 3H2O
2NaAl(OH)4 OR Al2O3 + 2NaOH
2NaAlO2 + H2O OR Al2O3 + 2OH‒ + 7H2O
2[Al(OH)4(H2O)2] ‒ OR Al2O3 + 2OH‒ + 3H2O
2[Al(OH)4] ‒OR Al2O3 + 2OH−
2AlO2 − + H2O SO3 + NaOH
NaHSO4 OR SO3 + 2NaOH
Na2SO4 + H2O [1] [1] [1] [1] [4]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 22 © Cambridge International Examinations 2015 Question Mark Scheme Mark Total [18] 2 (a) (i) 2PbS + 3O2
2PbO + 2SO2 reagents and formulae balancing [1] [1] [2] (ii) S (is oxidised) –2 to (+)4 O (is reduced) 0 to –2 [1] [1] [2] (b) (i) T = 400 – 600 °C (chosen as a compromise because) High T increases rate ora High T decreases yield / moves eqm left / makes less SO3 as forward reaction exothermic ora [1] [1] [1] [3] (ii) High pressure increases rate as collision frequency increases ora High pressure moves eqm right / favours forward reaction as more moles on left ora Uneconomic to use high pressures / high yield at low pressure [1] [1] [1] [3] (c) (i) Reaction (too) exothermic / acid spray produced [1] [1] (ii) SO3 + H2SO4
H2S2O7 H2S2O7 + H2O
2H2SO4 [1] [1] [2] (d) Preservative owtte antimicrobial / antioxidant / reducing agent [1] [1] [2] (e) (i) 12.35 × 0.01 / 1000 = 1.235 × 10–4 [1] [1] (ii) 1.235 × 10–4 × 1000 / 50 = 2.47 × 10–3 [1] [1] (iii) 2.47 × 10–3 × 64.1 = 0.158327 g = 158 (3 sf only) [1] [1] [18] 3 (a) (i) Bond breaking = Cl-Cl = 242 C-H = 410 = 652 kJ Bond forming = C-Cl = 340 H-Cl = 431 = 771 kJ Enthalpy change = 652 – 771 = –119 [1] [1] [1] [3] (ii) UV / High T / sunlight [1] [1]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9701 22 © Cambridge International Examinations 2015 Question Mark Scheme Mark Total (iii) Initiation Cl2
2Cl• Propagation C2H6 + Cl•
•C2H5 + HCl •C2H5 + Cl2
C2H5Cl + Cl• Termination •C2H5 + •C2H5
C4H10 All three names correctly assigned [1] [1] [1] [1] [1] [5] (b) (i) ethene [1] [1] (ii) KOH / NaOH ethanolic AND heat / reflux [1] [1] [2] (iii) H2 AND Pt or Ni (catalyst) [1] [1] [13] 4 (a) (i) A = CH3CH2CH2CH2CHO B = CH3CH2CH(CH3)CHO C = (CH3)2CHCH2CHO D = (CH3)3CCHO [1] [1] [1] [1] [4] (ii) [1+1] [2] (b) (i) Fehling’s / Benedict’s OR Tollens’ OR dichromate OR manganate Warm / heat Fehling’s / Benedict’s =(Brick)-red ppt Tollens’ = silver / mirror OR grey/black precipitate Dichromate = orange to green with the aldehyde / A-D Manganate = purple to colourless [1] [1] [1] [3] (ii) (2,4-)DNP(H) / Brady’s reagent Orange / yellow / red-orange / yellow-orange ppt [1] [1] [2] [11] C H CH CH3 CH2 O C H3 H2 CH C CH3 CH2 O CH3 H2 H