Cambridge A Level Chemistry 9701 — 2014 May/June Paper 2 · Variant 3

This document consists of 9 printed pages and 3 blank pages. [Turn over IB14 06_9701_23/3RP © UCLES 2014  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 9701/23 Paper 2 Structured Questions AS Core May/June 2014 1 hour 15 minutes Candidates answer on the Question Paper. Additional Materials: Data Booklet Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level

2 9701/23/M/J/14 © UCLES 2014 Answer all the questions in the spaces provided. 1 (a) Defi ne the term mole. … … [1] (b) 10 cm3 of a gaseous hydrocarbon, CxHy, was reacted with 100 cm3 of oxygen gas, an excess. The fi nal volume of the gaseous mixture was 95 cm3. This gaseous mixture was treated with concentrated, aqueous sodium hydroxide to absorb the carbon dioxide present. This reduced the gas volume to 75 cm3. All gas volumes were measured at 298 K and 100 kPa. (i) Write an equation for the reaction between sodium hydroxide and carbon dioxide. … [1] (ii) Calculate the volume of carbon dioxide produced by the combustion of the hydrocarbon. volume of CO2 produced = … cm3 [1] (iii) Calculate the volume of oxygen used up in the reaction with the hydrocarbon. volume of O2 used = … cm3 [1] (iv) Use your answers to (b)(ii) and (b)(iii), together with the initial volume of hydrocarbon, to balance the equation below. …CxHy + …O2  …CO2 + zH2O [2] (v) Deduce the values of x, y and z in the equation in (iv). x = … y = … z = … [3]

3 9701/23/M/J/14 © UCLES 2014 [Turn over (c) Another hydrocarbon, W, with the formula C4H8, reacts with hydrogen bromide, HBr, to give two products X and Y. X and Y are structural isomers of molecular formula C4H9Br. Reaction of X with aqueous alkali produces an alcohol, Z, that has no reaction with acidifi ed dichromate(VI). (i) Give the structures and names of the compounds W, X, Y, and Z W X … … Y Z … … [4] (ii) When W reacts with hydrogen bromide, more X than Y is produced. Explain why. … … … … [2] [Total: 15]

4 9701/23/M/J/14 © UCLES 2014 2 A sample of a hydrated double salt, Cu(NH4)x(SO4)2.6H2O, was boiled with an excess of sodium hydroxide. Ammonia was given off. The ammonia produced was absorbed in 40.0 cm3 of 0.400 mol dm–3 hydrochloric acid. The resulting solution required 25 cm3 of 0.12 mol dm–3 sodium hydroxide to neutralise the excess acid. (a) Write the ionic equation for the reaction between ammonium ions and hydroxide ions. … [1] (b) (i) Calculate the amount, in moles, of hydrochloric acid in 40.0 cm3 of 0.400 mol dm–3 solution. [1] (ii) Calculate the amount, in moles, of sodium hydroxide needed to neutralise the excess acid. This will be equal to the amount of hydrochloric acid left in excess. [1] (iii) Calculate the amount, in moles, of hydrochloric acid that reacted with ammonia. [1] (iv) Calculate the amount, in moles, of ammonium ions in the sample of the double salt. [1] (v) The sample contained 0.413 g of copper. Use this information and your answer to (iv) to calculate the value of x in Cu(NH4)x(SO4)2.6H2O. [2] (vi) Calculate the Mr of Cu(NH4)x(SO4)2.6H2O. [1] [Total: 8]

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6 9701/23/M/J/14 © UCLES 2014 3 Nitrogen dioxide, NO2, can enter the atmosphere in a variety of ways. (a) (i) State one natural and one man-made source of atmospheric NO2. natural … man-made … [1] (ii) Write an equation to show how NO2 leads to the formation of nitric acid in acid rain. … [1] (iii) Use equations to illustrate the catalytic role of NO2 in the formation of sulfuric acid in acid rain. … … … [3] (b) Nitrogen dioxide exists in equilibrium with dinitrogen tetroxide, N2O4. 2NO2(g) N2O4(g) 2.00 mol of dinitrogen tetroxide was sealed in a container at 350 K. After equilibrium had been established the total pressure was 140 kPa and the mixture of gases contained 1.84 mol of dinitrogen tetroxide. (i) Give the expression for the equilibrium constant, Kp, for this equilibrium. Kp = [1] (ii) Calculate the number of moles of NO2 present at equilibrium. [1] (iii) Calculate the total number of moles of gas present at equilibrium and hence the mole fraction of each gas present at equilibrium. [2]

7 9701/23/M/J/14 © UCLES 2014 [Turn over (iv) Calculate the partial pressure of each gas present at equilibrium. [2] (v) Calculate the value of the equilibrium constant, Kp, at 350 K. Give your answer to three signifi cant fi gures and include the units. Kp = … units = … [2] [Total: 13]

8 9701/23/M/J/14 © UCLES 2014 4 The halogens and their compounds have a wide variety of uses and the chemical and physical properties of the elements show regular patterns related to their positions in Group VII. (a) Chlorine, bromine and iodine all react with hydrogen. (i) State the trend in the reactivities of the halogens with hydrogen. … … [1] (ii) Explain this trend in terms of bond energies. … … … [2] (b) In the laboratory it is not very convenient to prepare hydrogen halides from their elements. Hydrogen halides can be prepared from their salts. (i) Write an equation for the reaction of calcium chloride, CaCl 2, with concentrated sulfuric acid. … [1] (ii) Explain why hydrogen iodide is not prepared in this way. … … [1] (iii) When potassium bromide, KBr, reacts with concentrated sulfuric acid, sulfur dioxide, SO2, is produced. State what you would see and write an equation for this reaction. … … [3]

9 9701/23/M/J/14 © UCLES 2014 [Turn over (c) (i) Give the structures of the four structural isomers of C4H9Br and identify each as primary, secondary or tertiary. … … … … [4] (ii) Name the isomer of C4H9Br that contains a chiral centre and draw the three-dimensional structures of the two optical isomers. name … structures [3] (d) Aqueous silver nitrate solution was added to separate tubes containing chloroethane, bromoethane and iodoethane. The tubes were heated in a water bath. A yellow precipitate appeared fi rst in the tube containing iodoethane, followed by a cream precipitate in the tube containing bromoethane and fi nally a white precipitate appeared in the tube containing chloroethane. Explain these observations. … … … … … … [2]

10 9701/23/M/J/14 © UCLES 2014 (e) (i) Give the full name of the mechanism for the reaction between aqueous sodium hydroxide and bromoethane. … [2] (ii) Complete the diagram below to represent this mechanism. Include all necessary curly arrows, partial charges and lone pairs. C H Br H H C H HO– H C H OH + Br – H H C H H [2] (f) In the past, CFCs such as CF3Cl were widely used as refrigerants. (i) State a property of CFCs which makes them suitable for use as refrigerants. … [1] (ii) State the damaging effect of CFCs in the upper atmosphere. … Explain your answer. … … … [2] [Total: 24]

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CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level MARK SCHEME for the May/June 2014 series 9701 CHEMISTRY 9701/23 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 2014 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 LEVEL – May/June 2014 9701 23 © Cambridge International Examinations 2014 Question Mark Scheme – 9701 / 23 Mark Total mark 1 (a) the amount of substance containing 6(.02) x 1023 (fundamental) particles of that substance (or; the amount of substance containing as many particles as there are atoms in 12 g of carbon-12) (1) [1] (b) (i) 2NaOH + CO2
Na2CO3 + H2O allow ionic equations or formation of NaHCO3 (1) [1] (ii) 95 – 75 = 20 cm3 (1) [1] (iii) excess oxygen = 75 cm3 so used = 25 cm3 (1) [1] (iv) 2CxHy + 5O2
4CO2 + zH2O (2) [2] (v) x = 2; y = 2; z = 2 (or z = 1 if CxHy + 2.5O2
2CO2 + zH2O) (1+1+1) [3] (c) (i) W = (CH3)2C=CH2 = 2–methylpropene X = (CH3)2CBrCH3 = 2–bromo–2–methylpropane Y = (CH3)2CHCH2Br = 1–bromo–2–methylpropane Z = (CH3)3COH = 2–methylpropan–2–ol (1) (1) (1) (1) [4] (ii) Markovnikov addition / H adds to C with most Hs tertiary carbocation more stable than primary inductive effect of three alkyl groups owtte (1) (1) (1) [Max 2] Total 15

Page 3 Mark Scheme Syllabus Paper GCE AS LEVEL – May/June 2014 9701 23 © Cambridge International Examinations 2014 2 (a) NH4 + + OH–
NH3 + H2O (1) [1] (b) (i) Initial acid = 40 × 0.4 / 1000 = 0.016 (mol) (1) [1] (ii) 25 x 0.12 = 3.0 × 10–3 (mol) (of OH– used) 1000 (1) [1] (iii) excess acid = OH– = 0.003 acid reacted = 0.016 – 0.003 = 0.013 (mol) (1) [1] (iv) NH4 +:H+ = 1:1 so = 0.013 (mol NH4 +) (1) [1] (v) amount of Cu = mass / Mr = 0.413 / 63.5 = 6.5 × 10–3 (mol) so Cu:NH4 = 0.0065:0.013 = 1:2 so x = 2 (1) (1) [2] (vi) Mr = 399.7 (1) [1] Total 8

Page 4 Mark Scheme Syllabus Paper GCE AS LEVEL – May/June 2014 9701 23 © Cambridge International Examinations 2014 3 (a) (i) (reaction between atmospheric N2 and O2) due to lightning / biological processes or bacteria in soil AND in car engines / power stations / metal refining / furnaces (1) [1] (ii) 2NO2 + H2O
HNO2 + HNO3 OR 2NO2 + H2O + 1 / 2O2
2HNO3 OR 3NO2 + H2O
2HNO3 + NO (1) [1] (iii) SO2 + NO2
SO3 + NO NO + 1 / 2O2
NO2 SO3 + H2O
H2SO4 (1) (1) (1) [3] (b) (i) Kp = pN2O4 / (pNO2)2 (1) [1] (ii) moles of NO2 = 0.32 (1) [1] (iii) x(N2O4) = 1.84 / 2.16 = 0.85 x(NO2) = 0.32 / 2.16 = 0.15 ecf from (b)(ii) (1) (1) [2] (iv) pN2O4 = 0.85 × 140 = 119 (kPa) pNO2 = 0.15 × 140 = 21 (kPa) ecf from (b)(iii) (1) (1) [2] (v) Kp = 119 / 212 = 0.270 kPa–1 ecf from (b)(i) and (b)(iv) (2) [2] Total 13

Page 5 Mark Scheme Syllabus Paper GCE AS LEVEL – May/June 2014 9701 23 © Cambridge International Examinations 2014 4 (a) (i) decreases down the group ora (1) [1] (ii) X–X bond strength decreases from Cl – Cl to I – I But decreasing strength of H–X down group more significant (1) (1) [2] (b) (i) CaCl 2 + H2SO4
CaSO4 + 2HCl OR CaCl 2 + 2H2SO4
Ca(HSO4)2 + 2HCl (1) [1] (ii) HI / I– reduces / is oxidised by conc H2SO4 / because iodine is produced instead (1) [1] (iii) brown gas / fumes produced 2H2SO4 + 2KBr
SO2 + Br2 + 2H2O + K2SO4 (or ionic) (1) (1+1) [3] (c) (i) CH3CH2CH2CH2Br primary CH3CH2CHBrCH3 secondary (CH3)2CHCH2Br primary (CH3)3CBr tertiary (1) (1) (1) (1) [4] (ii) 2-bromobutane C CH2 C H3 H Br CH3 C C H2 C H3 H Br CH3 (1) (1+1) [3] (d) halide ions liberated (by hydrolysis of halogenoalkanes)form precipitate with Ag+ OR Ag+ + X–
AgX order due to decreasing bond strength (C – I<C – Br<C – Cl ) (1) (1) [2]

Page 6 Mark Scheme Syllabus Paper GCE AS LEVEL – May/June 2014 9701 23 © Cambridge International Examinations 2014 (e) (i) nucleophilic substitution (2) [2] (ii) M1 = curly arrow from lone pair on OH–; M2 for curly arrow from C-Br bond to Br AND dipole (2) [2] (f) (i) inert or volatile owtte (1) [1] (ii) destroy ozone (in stratosphere) C–Cl bond broken by UV / free radicals produced (1) (1) [2] Total 24 C C H H H H Br H O H - C C H H H H OH H + Br - δ+ δ−