Cambridge A Level Chemistry 9701 — 2014 May/June Paper 2 · Variant 1

This document consists of 8 printed pages. [Turn over IB14 06_9701_21/2RP © 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 9701/21 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 9701/21/M/J/14 © UCLES 2014 Answer all the questions in the spaces provided. 1 (a) Explain what is meant by the term ionisation energy. … … … [3] (b) The fi rst seven ionisation energies of an element, A, in kJ mol–1, are 1012 1903 2912 4957 6274 21 269 25 398. (i) State the group of the Periodic Table to which A is most likely to belong. Explain your answer. … … … … [2] (ii) Complete the electronic confi guration of the element in Period 2 that is in the same group as A. 1s2 … [1] (c) Another element, Z, in the same period of the Periodic Table as A, reacts with chlorine to form a compound with empirical formula ZCl 2. The percentage composition by mass of ZCl 2 is Z, 31.13; Cl , 68.87. (i) Defi ne the term relative atomic mass. … … … [2] (ii) Calculate the relative atomic mass, Ar, of Z. Give your answer to three signifi cant fi gures. Ar of Z = … [2]

3 9701/21/M/J/14 © UCLES 2014 [Turn over (d) The chlorides of elements in Period 3 of the Periodic Table show different behaviours on addition to water, depending on their structure and bonding. (i) Write equations to show the behaviour of sodium chloride, NaCl , and silicon chloride, SiCl 4 , when separately added to an excess of water. NaCl … SiCl 4 … [2] (ii) State and explain the differences in behaviour of these two chlorides when added to water, in terms of their structure and the bonding found in the compounds. … … … … … … [4] (e) Sulfur reacts with fl uorine to form SF6. State the shape and bond angle of SF6. shape of SF6 … bond angle of SF6 … [2] [Total: 18]

4 9701/21/M/J/14 © UCLES 2014 2 The commonest form of iron(II) sulfate is the heptahydrate, FeSO4.7H2O. On heating at 90 C this loses some of its water of crystallisation to form a different hydrated form of iron(II) sulfate, FeSO4.xH2O. 3.40 g of FeSO4.xH2O was dissolved in water to form 250 cm3 of solution. A 25.0 cm3 sample of this solution was acidifi ed and titrated with 0.0200 mol dm–3 potassium manganate(VII). In this titration 20.0 cm3 of this potassium manganate(VII) solution was required to react fully with the Fe2+ ions present in the sample. (a) The MnO4 – ions in the potassium manganate(VII) oxidise the Fe2+ ions in the acidifi ed solution. (i) Explain, in terms of electron transfer, the meaning of the term oxidise in the sentence above. … … [1] (ii) Complete and balance the ionic equation for the reaction between the manganate(VII) ions and the iron(II) ions. MnO4 –(aq) + 5Fe2+(aq) + …H+(aq)  …(aq) + 5Fe3+(aq) + …H2O(l) [3] (b) (i) Calculate the number of moles of manganate(VII) used in the titration. [1] (ii) Use the equation in (a)(ii) and your answer to (b)(i) to calculate the number of moles of Fe2+ present in the 25.0 cm3 sample of solution used. [1] (iii) Calculate the number of moles of FeSO4.xH2O in 3.40 g of the compound. [1] (iv) Calculate the relative formula mass of FeSO4.xH2O. [1] (v) The relative formula mass of anhydrous iron(II) sulfate, FeSO4, is 151.8. Calculate the value of x in FeSO4.xH2O. [1] [Total: 9]

5 9701/21/M/J/14 © UCLES 2014 [Turn over 3 (a) In this question, K, L and M refer to a halogen atom or halide ion. For each part question, read the information and complete the answer lines below. (i) When concentrated sulfuric acid is added to solid NaK, white fumes are produced that turn damp blue litmus paper red. No other colour changes are observed. identity of K = … equation for reaction … explanation of observation … … [3] (ii) When silver nitrate solution is added to an aqueous solution of NaL, a precipitate forms that remains after the addition of concentrated ammonia solution. identity of L = … colour of precipitate … equation for reaction … [3] (iii) M2 is a liquid at room temperature with a boiling point higher than that of chlorine but lower than that of iodine. identity of M = … explanation … … … … … [2]

6 9701/21/M/J/14 © UCLES 2014 (b) The diagram below is a simplifi ed representation of a diaphragm cell. + – titanium anode diaphragm steel cathode concentrated brine product D product B product C (i) Identify each of the products. B … C … D … [3] (ii) Give the equations for the two electrode reactions. anode … cathode … [2] [Total: 13]

7 9701/21/M/J/14 © UCLES 2014 [Turn over 4 Alkanes and alkenes both react with bromine. (a) Explain how and why bromine can be used to distinguish between an alkene and an alkane. … … … [2] (b) The reaction of ethane with bromine forms a mixture of products. (i) State the essential conditions for this reaction to occur. … [1] (ii) Give the full name of the mechanism of this reaction. … [2] (iii) Give the equation for a termination step that could occur, producing a hydrocarbon. … [1] (iv) Give the equation for one propagation step involved in the formation of dibromoethane from bromoethane during this reaction. … [1] (c) The reaction of ethene with bromine forms a single product. (i) Give the full name of the mechanism of this reaction. … [2] (ii) Complete the diagram below to illustrate this mechanism. Include all relevant charges, partial charges, curly arrows and lone pairs. C H H H C H C H H H C H Br Br Br Br [4]

8 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. 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. 9701/21/M/J/14 © UCLES 2014 (d) Chloroethene can be polymerised to form a polymer commonly known as PVC. Draw a diagram of the structure of PVC including three repeat units. [2] (e) Chloroethane undergoes a series of reactions as shown in the diagram below. C H H H C H H Cl reaction 1 NaCN product P product Q C C H H H H OH–(aq) (i) Give the reagent and conditions necessary for reaction 1. … … [2] (ii) Give the skeletal formula of product P. [1] (iii) Give the displayed formula and the name of product Q. … [2] [Total: 20]

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2014 series 9701 CHEMISTRY 9701/21 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/A LEVEL – May/June 2014 9701 21 © Cambridge International Examinations 2014 Question Mark Scheme Mark Total 1 (a) The amount of energy required / energy change / enthalpy change when one electron is removed from each atom / (cat)ion in one mol of gaseous atoms / (cat)ions OR energy change when 1 mole of electrons is removed from one mole of gaseous atoms / ions X(g) → X+(g) + e– gains 2 marks 1 1 1 3 (b) (i) Group V / 5 / 15 Big difference between fifth and sixth ionisation energies 1 1 2 (ii) 1s2 2s2 2p3 ecf from (b)(i) if period 2 1 1 (c) (i) (Weighted) mean / average mass of an atom(s) (of an element) Relative to 1 / 12th of (the mass of an atom of) carbon-12 OR relative to carbon-12 which is (exactly) 12 (units) allow as an expression 1 1 2 (ii) Z Cl 2 : 1 35.5 68.87 A 31.13 r = So 2 31.13/ 68.87/35.5 = r A 3s.f. to 32.1 32.0923 68.87 35.5 31.13 2 r A = = × × = Allow alternative correct methods 1 1 2

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 21 © Cambridge International Examinations 2014 Question Mark Scheme Mark Total (d) (i) NaCl (+ aq )
Na+ + Cl – NaCl + H2O
Na+ + Cl – + H2O SiCl 4 + 2H2O
SiO2 + 4HCl SiCl 4 + 4H2O
Si(OH)4 + 4HCl SiCl 4 + 4H2O
SiO2.2H2O + 4HCl Allow correct equation with other molar amounts of water 1 1 2 (ii) NaCl is ionic AND giant / lattice NaCl dissolves / does not react SiCl 4 is covalent AND molecular / simple SiCl 4 is hydrolysed / reacts 1 1 1 1 4 (e) shape of SF6 = Octahedral bond angle = 90° 1 1 2 18 2 (a) (i) (The MnO4 ‒ ions cause the Fe2+ ions to) lose electrons owtte / ora 1 1 (ii) MnO4 –(aq) + 5Fe2+(aq) + 8H+(aq)
Mn2+(aq) + 5Fe3+(aq) + 4H2O(l) 1+1+1 3 (b) (i) (mol) 4 10 4(.00) 1000 0.020 20.0 − × = × 1 1 (ii) MnO4 – : Fe2+ = 1 : 5 so amount of Fe2+ = 5 × 4.00 × 10‒4 = 2(.00) × 10‒3 (mol) ecf from (b)(i) 1 1 (iii) 2.00 × 10‒3 × 250 / 25 = 0.02(00) (mol) ecf from (b)(ii) 1 1

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 21 © Cambridge International Examinations 2014 Question Mark Scheme Mark Total (iv) 3.40 / 0.02 = 170 ecf from (b)(iii) 1 1 (v) 170 – 151.8 = 18.2 18.2 / 18 = 1.01 x = 1 ecf from (b)(iv) if appropriate 1 1 9 3 (a) (i) K = Cl– / chloride / F– / fluoride H2SO4 + 2NaCl
Na2SO4 + 2HCl (or equation with F or K for Cl) OR H2SO4 + NaCl
NaHSO4 + HCl (or equation with F or K for Cl ) ecf from identity of K so long as halide HK is acidic / HK is a gas / an acidic gas is produced 1 1 1 3 (ii) L = I– / iodide colour = yellow ecf from identity of L i.e. Cl – (white) or Br– (cream) Ag+ + I‒
AgI (or equation with L) AgNO3 + NaI → AgI + NaNO3 (or equation with L) ecf from identity of L so long as halide 1 1 1 3 (iii) Br2 / bromine has fewer electrons than iodine / more electrons than chlorine intermolecular / van der Waals’ forces (in Br2 / M2) weaker than in iodine / stronger than in chlorine 1 1 2 (b) (i) B = chlorine / Cl 2 C = hydrogen / H2 D = sodium hydroxide / NaOH 1 1 1 3

Page 5 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 21 © Cambridge International Examinations 2014 Question Mark Scheme Mark Total (ii) anode: 2Cl –
Cl 2 + 2e– cathode: 2H+ + 2e–
H2 OR 2H2O + 2e–
2OH– + H2 1 1 2 13 4 (a) decolourisation with an alkene at room conditions / quickly / easily / OR alkane needs higher temp / UV / is slow at room conditions double / π / pi bond / C = C present in alkenes 1 1 2 (b) (i) UV light / sunlight / high temperature 1 1 (ii) (Free) radical Substitution 1 1 2 (iii) •C2H5 + •C2H5
C4H10 1 1 (iv) C2H5Br + Br•
•C2H4Br + HBr OR •C2H4Br + Br2
C2H4Br2 + Br• 1 1 (c) (i) Electrophilic Addition 1 1 2

Page 6 Mark Scheme Syllabus Paper GCE AS/A LEVEL – May/June 2014 9701 21 © Cambridge International Examinations 2014 Question Mark Scheme Mark Total (ii) 4 (d) minimum of three repeat units 2 2 (e) (i) NaOH/KOH ethanolic / alcoholic AND heat / reflux 1 1 2 (ii) 1 1 (iii) Propanenitrile / propanonitrile / propionitrile / ethyl cyanide / cyanoethane 1 1 2 20 C C H H H H Br Br C C H H Br Br H H δ+ δ− C C + H H Br H H Br - M1: 2 correct curly arrows M2: dipole M3: Correct intermediate M4: Curly arrow from lone pair on Br− to C+ C C C C C C H H H H Cl H H H Cl H H Cl H H H H H OH M1: 2 correct curly arrows M2: correct dipole M3: correct intermediate M4: curly arrow from lone pair on Br− to C+ C C C N H H H H H