Cambridge A Level Chemistry 9701 — 2014 Oct/Nov Paper 4 · Variant 3

This document consists of 19 printed pages and 1 blank page. [Turn over IB14 11_9701_43/4RP © UCLES 2014 *5493011778* For Examiner’s Use 1 2 3 4 5 6 7 8 9 Total 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. Section A Answer all questions. Section B 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 9701/43 Paper 4 Structured Questions October/November 2014 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet Cambridge International Examinations Cambridge International Advanced Level

2 9701/43/O/N/14 © UCLES 2014 Section A Answer all the questions in the spaces provided. 1 (a) Chlorine exists naturally as a mixture of two isotopes, 35Cl and 37Cl , in the abundance ratio of 3 : 1. The mass spectrum of chlorine consists of fi ve peaks. (i) Suggest the mass numbers for these fi ve peaks and the identities of the species responsible. mass number formula of species (ii) Predict the ratios of the abundances of the three species with the highest mass numbers. ratio of abundances = … [4] (b) Strontium chloride, SrCl 2, can be used to produce a red colour in fi reworks. (i) Draw the ‘dot-and-cross’ diagram for strontium chloride. Show outer shell electrons only.

3 9701/43/O/N/14 © UCLES 2014 [Turn over (ii) Use the following data, together with relevant data from the Data Booklet, to calculate a value for the lattice energy of strontium chloride. You may fi nd it helpful to construct a Born-Haber cycle. electron affi nity per mole of chlorine atoms –349 kJ mol–1 standard enthalpy of atomisation of Sr(s) +164 kJ mol–1 standard enthalpy of formation of SrCl 2(s) –830 kJ mol–1 lattice energy = … kJ mol–1 [5] (c) Strontium nitrate, Sr(NO3)2, can also be used to produce a red colour in fi reworks. (i) Strontium nitrate can easily be prepared from strontium carbonate, SrCO3. Suggest an equation for this preparation of strontium nitrate. … (ii) Write an equation for the reaction that occurs when strontium nitrate is heated. … [2] (d) Describe and explain the trend in the thermal stabilities of the nitrates of the Group II elements. … … … … … [3] [Total: 14]

4 9701/43/O/N/14 © UCLES 2014 2 (a) Bromate(V) ions, BrO3 –, react with bromide ions in the presence of acid to produce bromine. Write an ionic equation for this reaction. … … [2] (b) The initial rate of this reaction was measured, starting with different concentrations of the three reactants. The following results were obtained. experiment number [BrO3 –] / mol dm–3 [Br –] / mol dm–3 [H+] / mol dm–3 initial rate / mol dm–3 s–1 1 0.040 0.020 0.50 2.64 × 10–4 2 0.040 0.020 1.00 1.06 × 10–3 3 0.040 0.080 0.50 1.06 × 10–3 4 0.080 0.020 0.50 5.21 × 10–4 (i) Use the data in the table to determine the order with respect to each reactant. Show your reasoning. … … … … (ii) Write the rate equation for this reaction. … (iii) Use the results of experiment 1 to calculate the rate constant, k, for this reaction. Include the units of k. rate constant, k = … units … [6] [Total: 8]

5 9701/43/O/N/14 © UCLES 2014 [Turn over 3 Transition elements have characteristic properties due to their partially-fi lled d orbitals. (a) (i) Which two elements in the fi rst row of the d-block have only one electron in the 4s orbital of their neutral atoms? … (ii) The d orbitals in an isolated transition metal atom or ion are described as being degenerate. What is meant by the term degenerate? … (iii) Sketches of the shapes of the atomic orbitals from the d subshell are shown. In an octahedral complex, the d orbitals are split into two groups at different energy levels. On the diagram below, write an ‘H’ in the box under each of the orbitals at the higher energy level. z y x z y x z y x y x z z y x [4]

6 9701/43/O/N/14 © UCLES 2014 (b) The following scheme shows some reactions of Cu2+(aq). Cu2+(aq) pale blue precipitate A solution of B solution of C [CuCl 2]–(aq) concentrated HCl excess NH3(aq) heat with Cu(s) a few drops of NH3(aq) (i) Suggest the formula of each of the following. A … B … C … (ii) State the colour of the following solutions. solution of B … solution of C … (iii) Name the type of reaction that occurs when C is heated with copper. … Deduce the role of the copper metal in this reaction. … [6] (c) When the solution containing the complex [CuCl 2]– is poured into water, a precipitate of CuCl is formed. CuCl is white because it does not absorb visible light. Explain why CuCl does not absorb visible light. … … … [2]

7 9701/43/O/N/14 © UCLES 2014 [Turn over (d) The complex ion [Cr(H2O)6]3+ is coloured because it absorbs visible light. The absorption spectrum for [Cr(H2O)6]3+ is shown below. absorbance wavelength / nm 400 violet red 500 600 Suggest the colour of this complex ion. Explain your answer. … … [2] [Total: 14]

8 9701/43/O/N/14 © UCLES 2014 4 (a) The following circuits were set up using aqueous hydrochloric and aqueous ethanoic acids as electrolytes. Assume that the two circuits were identical apart from the electrolyte. graphite electrodes 1 mol dm–3 HCl (aq) bulb 1 switch graphite electrodes 1 mol dm–3 CH3CO2H(aq) bulb 2 switch When the switches were closed, bulb 1 was brighter than bulb 2. Explain why. … … … … [2] (b) (i) State what is meant by a buffer solution. … … (ii) Outline how a buffer solution can be prepared from ethanoic acid and a named base. … … [4] (c) Amino acids such as alanine, CH3CH(NH2)CO2H, can act as a buffer solution. Construct two equations to illustrate this. equation 1 equation 2 [2]

9 9701/43/O/N/14 © UCLES 2014 [Turn over (d) Tartaric acid is present in many plants. O O OH OH OH HO tartaric acid (i) Tartaric acid has two dissociation constants, K1 and K2, for which the pKa values are 2.99 and 4.40. Suggest equations showing the two dissociations that give rise to these pKa values. pKa 2.99 pKa 4.40 (ii) One stereoisomer of tartaric acid is shown. CO2H HO2C OH HO H H Complete the diagrams showing two other stereoisomers of tartaric acid. CO2H CO2H [4] [Total: 12]

10 9701/43/O/N/14 © UCLES 2014 5 L-DOPA is used in the treatment of Parkinson's disease. It can be prepared from vanillin. HO NH2 CO2H HO HO H CH3O O L-DOPA vanillin (a) L-DOPA and vanillin each contain an aromatic benzene ring. Describe, with the aid of a diagram, the bonding and shape of a molecule of benzene, C6H6. … … … … … … [5]

11 9701/43/O/N/14 © UCLES 2014 [Turn over (b) A student carried out some reactions with samples of L-DOPA and vanillin using reagents X, Y and Z. ● Reagent X reacted with L-DOPA and with vanillin. ● Reagent Y reacted with L-DOPA but not with vanillin. ● Reagent Z reacted with vanillin but not with L-DOPA. Assume that the CH3O– group in vanillin does not react. Suggest possible identities of reagents X, Y and Z and give the structures of the organic products that were formed. Reagent X … product with L-DOPA product with vanillin Reagent Y … product with L-DOPA Reagent Z … product with vanillin [7] [Total: 12]

12 9701/43/O/N/14 © UCLES 2014 6 Methoxetamine is a derivative of the pharmaceutical drug, ketamine. O OCH3 NHCH2CH3 methoxetamine (a) (i) What is the molecular formula of methoxetamine? … (ii) On the diagram above, circle any chiral centres that are present in methoxetamine. (iii) Name two functional groups in methoxetamine, in addition to the aryl group. … [4]

13 9701/43/O/N/14 © UCLES 2014 [Turn over (b) In the table, complete the structure of each of the compounds formed when methoxetamine is reacted with the following reagents. State the type of reaction in each case. reagent structure of product type of reaction (i) LiAl H4 OCH3 (ii) HCl (aq) OCH3 (iii) CH3COCl OCH3 [6] [Total: 10]

14 9701/43/O/N/14 © UCLES 2014 Section B Answer all the questions in the spaces provided. 7 (a) Explain what is meant by the term partition coeffi cient. … … [2] (b) When 20 cm3 of ethoxyethane were shaken with 75 cm3 of an aqueous solution containing 5.00 g of an organic compound, J, in 75 cm3 of water, it was found that 2.14 g of J were extracted into the ethoxyethane. Calculate the partition coeffi cient, Kpartition, of J between ethoxyethane and water. Kpartition = … [2] (c) In a new experiment ● 10 cm3 of ethoxyethane were shaken with 75 cm3 of an aqueous solution containing 5.00 g of J and the layers were separated. ● The aqueous layer was shaken with a second 10 cm3 portion of ethoxyethane and the layers were separated. ● The two organic layers were combined. Use the value of Kpartition you calculated in (b) to calculate the total mass of J extracted by this procedure. total mass of J = … [2] (d) Paper chromatography and gas / liquid chromatography both rely on the partition of compounds between mobile and stationary phases. (i) Identify the mobile phase in paper chromatography. … (ii) Suggest what type of liquid is used for the stationary phase in gas / liquid chromatography. …

15 9701/43/O/N/14 © UCLES 2014 [Turn over (iii) Both these techniques can be used to separate mixtures. State what you would measure in order to distinguish between the components in the mixture in 1. paper chromatography, … 2. gas / liquid chromatography. … [4] (e) A mixture of three compounds was analysed by paper chromatography using a non-polar solvent. The resulting chromatogram is shown. 3 2 1 mixture solvent front Identify which compound is responsible for each spot. compound spot CO2H CH2OH CO2H CO2H [1] [Total: 11]

16 9701/43/O/N/14 © UCLES 2014 8 (a) Analysis of a sample of DNA showed that 33% of the nitrogenous bases present was guanine. Calculate the percentages of the other bases in this sample of DNA. adenine …% cytosine …% thymine …% [2] (b) Many drug molecules are chiral, but are often produced as a mixture of optical isomers. (i) Suggest why a larger mass of the mixture is required than of a single optical isomer. … … (ii) Suggest a problem that might arise as a result of taking a mixture of optical isomers. … … [2]

17 9701/43/O/N/14 © UCLES 2014 [Turn over (c) There are four structural isomers with the molecular formula C5H10O that are aldehydes. (i) Draw the structures of these aldehydes. P Q R S (ii) The NMR spectrum of one of these isomers contains four absorptions. Which isomer P, Q, R or S gives this spectrum? isomer … (iii) Predict the number of absorptions that would be given by each of the other three isomers. isomer letter (P, Q, R or S) number of absorptions [6] [Total: 10]

18 9701/43/O/N/14 © UCLES 2014 9 (a) Polymers can be formed by addition or condensation polymerisation. Complete the table. polymer method of polymerisation nylon PVC (polychloroethene) Terylene [1] (b) Nomex is a polymeric material with excellent fl ame-resistant properties. It contains a polymer made from the two monomers shown below. NH2 H2N CO2H HO2C Draw the structure of the polymer showing two repeat units. The linkages between monomer units should be shown fully displayed. [2] (c) Proteins are natural polymers. Explain what is meant by the primary structure of a protein. … … … [1]

19 9701/43/O/N/14 © UCLES 2014 [Turn over (d) Use the diagram to show an example of how the α-helix secondary structure in proteins is stabilised. … … [2] (e) The tertiary structure of a protein is destroyed during the process of denaturation. Explain how this can occur by (i) the addition of alkali, … … (ii) the addition of Hg2+ ions, … … (iii) heating to 70 °C. … … [3] [Total: 9]

20 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. 9701/43/O/N/14 © UCLES 2014 BLANK PAGE

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Level MARK SCHEME for the October/November 2014 series 9701 CHEMISTRY 9701/43 Paper 4 (A2 Structured Questions), maximum raw mark 100 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 2014 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Que 1 estio (a) (b) (c) on ) (i (ii ) (i (ii ) (i ) ) ) ) ) P Ma 9:6 co co La = = – Sr age arki 6:1 orrec orrec attic +(–8 –21 rCO e 2 ng p ct ch ct el e en 830 46 O3 + poin harg lectr nerg ) – ( (kJ 2H Cam nt 35, cor at l ges rons gy = (+ 1 mol HNO mbr 37, rrect eas s = ∆H 64 l–1) O3
ridg , 70 t for st on Hf(Sr + 54
Sr e In , 72 rmul ne st rCl2 48 + r(NO nter © 2, 74 lae truc ) – ( + 10 O3)2 nati © Ca 4 cture (∆Ha 060 + C iona ambr m 3 3 7 7 7 e as atom( + 24 CO2 Mar al A ridge m/e 35 37 70 72 74 s a p (Sr) 42 + 2 + rk S A Le e Int posit + ∆ + (2 H2O Sche evel terna tive Hi1( × – O eme – O ation 35C 37C ion Sr) + –349 e Octo nal E ide 3 3 Cl 35C 37C Cl 37C + ∆H 9)) ober Exam enti 35Cl 37Cl Cl o Cl 35 Cl o Hi2(S r/No mina ity l l or 35C Cl or 37C Sr) + ovem ation Cl2 Cl2 + ∆H mbe ns 20 Hatom er 2 014 m(Cl 2014 l) + 4 2∆H Sy 9 Hea(C yllab 970 Cl)) bus 1 Pap 43 per 3 Ma 1 1 1 1 1 1 1 1 1 1 arks 1 1 1 1 1 1 1 1 1 1 Mark tota [4] [5] ks al

Page 3 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 (ii) Sr(NO3)2
SrO + 2NO2 + 0.5 O2 1 [2] (d) (down the group) nitrates become more stable / require a higher temperature to decompose as size/radius of ion increases OR charge density of ion decreases so polarisation/distortion of anion/nitrate ion/NO3 – /NO bond decreases 1 1 1 [3] 2 (a) BrO3 – + 5Br– + 6H+ → 3Br2 + 3H2O five correct species correct balancing 1 1 [2] (b) (i) [BrO3 –] 1st order and the concentration is x2, rate doubles OR evidence using expt 1 & 4 eg ratios [H+] 2nd order and the concentration is x2, rate x4 OR evidence using expt 1 & 2 [Br-] 1st order and the concentration is x4, rate x4 OR evidence using expt 1 & 3 eg ratios 1 1 1 (ii) (Rate =) k [BrO3 –][Br–][H+]2 1 (iii) k = 1.32 mol–3 dm9 s–1 1 1 [6] 3 (a) (i) chromium and copper 1 (ii) (all orbitals have the) same energy 1 (iii) correct id of one higher energy d orbital the other higher energy d orbital 1 1 [4]

Page 4 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 (b) (i) pale blue precipitate A Cu(OH)2 OR [Cu(OH)2(H2O)4] solution B [Cu(NH3)4(H2O)2]2+ OR [Cu(NH3)4]2+ solution C [CuCl4]2– 1 1 1 (ii) solution B royal / deep / dark blue OR violet-blue solution C yellow / green 1 1 (iii) redox OR oxidation of Cu OR reduction of Cu2+ AND reducing agent / reductant 1 [6] (c) 3d-shell is full / 3d10 / no vacant d-orbital / d-orbitals full electrons cannot move between orbitals OR transitions cannot occur 1 1 [2] (d) green / yellow orange / red AND blue / violet light is absorbed 1 1 [2] 4 (a) (HCl) stronger acid / more dissociated / ionised in solution (HCl has) more ions / higher concentration of ions 1 1 [2] (b) (i) A solution that resists changes in the pH / keeps pH fairly constant when small quantities / amounts / vols of acid / H+ or base / OH– are added 1 1 (ii) add (ethanoic acid) to NaOH OR an equation excess (ethanoic acid) OR mix with sodium ethanoate 1 1 [4] (c) CH3CH(NH2)COOH + H+
CH3CH(NH3 +)COOH CH3CH(NH2)COOH + OH–
CH3CH(NH2)COO– + H2O 1 1 [2]

Page 5 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 (d) (i) 1 1 (ii) HOOC COOH H O H H OH HOOC COOH O H H OH H HOOC COOH O H H H OH (S,R) (R,S) (R,R) any two of the above 2 [4] 5 (a) any five of these seven points. • σ-bonds are between C-C OR C-H • carbons are sp2 • rings of charge above and below the ring must be in diagram • presence of σ-bonds • electrons/bonds are delocalised • planar molecule/bond angles 120o • all C-C are the same length/have intermediate bond length between C-C & C=C 5 [5] OH O OH OH O O H O O OH OH O O H O O OH OH O O H O O OH OH O -O + H+ + H+ pKa 2.99 pKa 4.40

Page 6 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 (b) Reagent X e.g. Br2, HNO3, Na, NaOH, benzenediazonium salt / ion; RCOCl ; Fe3+ ; H2+Ni substituted product for L-DOPA & vanillin (examples given are for X = Br2 and NaOH) O H O H NH2 COOH Br O H H3CO H O Br or O - O H NH2 O O - O - H3CO H O Reagent Y e.g. HCl; Na2CO3, Mg, SOCl2, PCl5, ROH + c.H2SO4; HCl+NaNO2 / HNO2; CH3Cl Correct substituted product for L-DOPA O H O H NH3 + COOH Reagent Z e.g. acidified Cr2O7 2– ; 2,4-DNPH, hydrazine ; Fehling’s, Tollens’; HCN; HCN + NaCN; NaBH4 ; correct substituted product for vanillin O H O H OH O 1 2 1 1 1 1 [7] 6 (a) (i) C15H21NO2 1

Page 7 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 (ii) O OCH3 NHCH2CH3 ∗ 1 (iii) any two of ketone, amine or ether 2 [4]

Page 8 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 (b) (i) LiAlH4 NHCH2CH3 OH OCH3 reduction / nucleophilic addition (ii) HCl (aq) NH2CH2CH3 O OCH3 + (Cl-) acid-base / neutralisation (iii) CH3COCl O OCH3 N H3CH2C COCH3 acylation / condensation allow addition + elimination allow nucleophilic substitution 1 mark for each correct structure 1 mark for each correct reaction type 3 3 [6]

Page 9 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 7 (a) (ratio of) the concentrations / distribution / amount / mass of solute in two (immiscible) solvents at equilibrium OR equilibrium constant OR includes expression with K 1 1 [2] (b) Kpc = [J in ether]/[J in H2O] = (2.14/20)/(5–2.14/75) =2.81 OR 2.82 1 1 [2] (c) 1st extraction: 2.81 =(x/10)/(5.0–x)/75 2.81(5–x) = 7.5x x= 1.36 g 2nd extraction: 2.81 =(y/10)/(3.64–y)/75 2.81(3.64-y) = 7.5y y= 0.99 g 1 1 [2] (d) (i) water / solvent / named solvent 1 (ii) non-volatile liquid, for example mineral oil or at least a C15 hydrocarbon oil 1 (iii) 1. Rf (retardation factor) or distance travelled by solute and distance by solvent 2. retention time 1 1 [4]

Page 10 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 (e) CO2H 2 CH2OH 1 CO2H CO2H 3 1 [1] 8 (a) C = 33 % A = T = 17 % 1 1 [2] (b) (i) only one isomer may be active / be of therapeutic benefit 1 (ii) the other (stereo) isomer may cause harm / side effects 1 [2]

Page 11 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 (c) (i) structures of the following aldehydes: CHO CHO CHO CHO two correct structures = 1 mark two further correct structures – 1 mark 1 1 (ii) 3-methylbutanal 1 (iii) pentanal 5 absorptions 2-methylbutanal 5 absorptions dimethylpropanal 2 absorptions 1 1 1 [6] 9 (a) nylon, terylene – condensation; PVC – addition – all three correct 1 [1] (b) correct fully displayed formula of -CO-NH- unit correct polymer structure N H N C H O C N H O N H C O C O 1 1 [2] (c) sequence / order of amino acids (in the polypeptide chain) 1 [1] (d) hydrogen bond C=O and N-H in two different amino acids in the backbone diagram 1 1 [2]

Page 12 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2014 9701 43 © Cambridge International Examinations 2014 (e) (i) disrupts hydrogen/ionic bonds as –COOH/NH3 + is deprotonated OR –NH3 + + OH– → NH2 + H2O linked to hydrogen / ionic bond disrupted OR–COOH + OH– → –COO– + H2O linked to hydrogen / ionic bond disrupted 1 (ii) Hg2+ interferes with/breaks the disulfide bond / bridge not sulfite, sulfate, sulfur, sulfide OR -S-S- shown with Hg2+ in an equation OR disrupting ionic interactions linked to carboxyl / COO– groups 1 (iii) (Heat to 70 °C) breaks the van der Waals’ forces / hydrogen bonding 1 [3]