Cambridge A Level Chemistry 9701 — 2015 Oct/Nov Paper 4 · 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 fluid. 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 9701/42 Paper 4 Structured Questions October/November 2015 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet Cambridge International Examinations Cambridge International Advanced Level This document consists of 19 printed pages and 1 blank page. [Turn over IB15 11_9701_42/FP © UCLES 2015 *2492672497* For Examiner’s Use 1 2 3 4 5 6 7 8 9 10 Total

2 9701/42/O/N/15 © UCLES 2015 Section A Answer all the questions in the spaces provided. 1 (a) Calcium has atomic number 20. Complete the electronic structures for a calcium atom, 1s22s22p6… calcium ion in the +2 oxidation state. 1s22s22p6… [1] (b) Calcium nitrate, Ca(NO3)2, is used in fertilisers and can be prepared by an acid-base reaction. Write an equation for the preparation of calcium nitrate by an acid-base reaction. … [1] (c) (i) When anhydrous calcium nitrate is heated strongly, it decomposes to leave a white solid. Identify this white solid and suggest another observation for this reaction. … … [1] (ii) The ease of thermal decomposition of the Group II nitrates decreases down the group. Explain this trend. … … … [2]

3 9701/42/O/N/15 © UCLES 2015 [Turn over (d) (i) What is meant by the term standard enthalpy change of hydration, ? … … … [2] (ii) Use the following data to calculate the lattice energy, , of calcium nitrate, Ca(NO3)2(s). You may find it helpful to construct an energy cycle. enthalpy change value (Ca2+(g)) –1650 kJ mol–1 (NO3 –(g)) –314 kJ mol–1 enthalpy change of solution for Ca(NO3)2(s) –19 kJ mol–1 Ca(NO3)2(s) = … kJ mol–1 [3] (e) The standard enthalpy change of hydration for Ba2+, (Ba2+(g)), is –1305 kJ mol–1. Suggest an explanation for why the of the Ba2+ ion is less exothermic than the of the Ca2+ ion. … … … [2] [Total: 12]

4 9701/42/O/N/15 © UCLES 2015 2 (a) Complete the table to show the number of unpaired electrons in the outer shell of each of the gaseous atoms, Na to Ar. Na Mg Al Si P S Cl Ar number of unpaired electrons [3] (b) (i) Complete the table for the reactions of two Period 3 chlorides with water. Period 3 chloride observations pH of solution formed SiCl 4 PCl 5 [3] (ii) Write an equation for the reaction between SiCl 4 and H2O. … [1] [Total: 7]

5 9701/42/O/N/15 © UCLES 2015 [Turn over 3 The transition element iron is the most abundant element in the Earth’s core. (a) What is meant by the term transition element? … … [1] (b) In aqueous solution, iron can form complex ions which contain ligands. (i) Name the type of bonding that occurs between a ligand and a transition element. … [1] (ii) Which of the following species can act as a ligand? Complete the table by placing a tick () in the appropriate column to indicate whether the species can act as a ligand or not. species can act as a ligand cannot act as a ligand NO3 – BF3 H2NCH2CH2NH2 NH4 + [2] (c) Manganese ions, Mn2+(aq), show some similar chemical properties to those of copper(II) ions, Cu2+(aq). Use this information and the Data Booklet to suggest the formula of the manganese species formed in each of the following reactions. State the type of reaction taking place in each case. formula of manganese species formed type of reaction Mn2+(aq) + NaOH(aq) Mn2+(aq) + concentrated HCl Mn2+(aq) + H2O2(aq) [5] [Total: 9]

6 9701/42/O/N/15 © UCLES 2015 4 In aqueous solution, 2-chloro-2-methylpropane, (CH3)3CCl, reacts with sodium hydroxide, NaOH. This is a nucleophilic substitution reaction. (CH3)3CCl (aq) + NaOH(aq) → (CH3)3COH(aq) + NaCl (aq) (a) Show the mechanism for this reaction. Include all necessary curly arrows, lone pairs and relevant dipoles. [3] The rate of this reaction was investigated using a large excess of sodium hydroxide. (b) The graph below shows the results of the experiment. 0.60 0.50 0.40 0.30 0.20 0.10 0 0 20 40 60 80 100 120 140 160 time / s [(CH3)3CCl ] / mol dm–3

7 9701/42/O/N/15 © UCLES 2015 [Turn over The reaction is first order with respect to [(CH3)3CCl ]. This can be confirmed from the graph using half-lives. (i) What is meant by the half-life of a reaction? … … [1] (ii) Calculate the half-life for this reaction. Show all your working and show clearly any construction lines on the graph. [1] (iii) What would be the effect on the half-life of this reaction if the initial concentration of [(CH3)3CCl ] was doubled? … [1] (c) (i) Use the graph in (b) to determine the rate of reaction at 80 s. Show all your working. rate = … units … [2] The rate equation for this reaction is shown. rate = k [(CH3)3CCl ] (ii) Calculate the value of the rate constant, k, for this reaction and give its units. k = … units … [1] [Total: 9]

8 9701/42/O/N/15 © UCLES 2015 5 X is a metallic element. (a) (i) Draw a fully labelled diagram to show how the standard electrode potential, E o, of X2+(aq) / X(s) could be measured. [4] (ii) What are the conditions needed for the value measured to be a standard electrode potential? … [1] (iii) State the charge carriers that transfer current through the solutions, … the wire. … [1]

9 9701/42/O/N/15 © UCLES 2015 [Turn over (b) An electrochemical cell was set up consisting of an X2+(aq) / X(s) half-cell (E o = –0.40 V) and an Ag+(aq) / Ag(s) half-cell (E o = +0.80 V). (i) Write an equation for the reaction that would take place if the electrodes of this cell were connected by a wire. … [1] When the current was allowed to pass for a period of time, • the Ag electrode gained 1.30 g in mass, • the electrode made of metal X lost 0.67 g in mass. (ii) Calculate the Ar of metal X; hence suggest an identity for X. Show all your working. Use of the Data Booklet is relevant to this question. Ar = … X is … [4] [Total: 11]

10 9701/42/O/N/15 © UCLES 2015 6 Boron forms many useful compounds. (a) The compound diborane, B2H6, can be used as a rocket fuel. It can be prepared by the reaction of boron trifluoride, BF3, with sodium borohydride, NaBH4. Balance this equation. …BF3 + …NaBH4 → …B2H6 + …NaBF4 [1] (b) Primary and secondary alcohols can be formed by the reaction of carbonyl compounds with NaBH4, which is a source of hydride ions, H–. Complete the mechanism for the reaction of butanone with hydride ions, H–, and draw the intermediate in the box. Include all necessary curly arrows and relevant dipoles. CH2CH3 CH2CH3 O C intermediate OH C step 1 H+ H– H3C H3C H [3] (c) Borane, BH3, is used to synthesise alcohols from alkenes. The reaction occurs in two steps. The BH2 group from BH3 bonds to the least substituted carbon atom of the double bond, and the remaining H from BH3 bonds to the other carbon. CH3 H CH3 CH3 C C CH3 CH3 H BH2 C C + BH3 H step 1 [O] CH3 CH3 CH3 H OH C C H CH3 (i) Suggest the type of reaction in step 1. … [1]

11 9701/42/O/N/15 © UCLES 2015 [Turn over (ii) The diol Y can be prepared by the same method. CH3 CH3 H3C CH3 OH OH Y Draw the structure of the diene which could be used to prepare diol Y. [1] (d) Benzene, C6H6, and borazine, B3N3H6, have planar, cyclic structures. (i) Describe the structure of and bonding in benzene, C6H6. … … … … … … … [3] (ii) In borazine, B3N3H6, the boron and nitrogen atoms alternate around the ring. Each ring atom has a single hydrogen atom bonded to it. All boron-nitrogen bonds in borazine are 0.144 nm in length, whereas in simple compounds B–N and B=N bond lengths are 0.154 nm and 0.136 nm respectively. Suggest and draw the structure of borazine. [1] [Total: 10]

12 9701/42/O/N/15 © UCLES 2015 7 (a) Sunset Yellow is a yellow colouring agent used in food and drinks, which can be made by the following route. In step 3 of this synthesis, a phenol-like compound, S, reacts with intermediate T made from amine R. Assume that the –SO3 – Na+ group does not react. SO3 – Na+ SO3 – Na+ O2N step 1 step 2 + Sunset Yellow step 3 NaOH(aq) R (C6H6NSO3Na) T S Q OH Na+ –O3S N N (i) Suggest structures for compounds R, S and T and draw them in the boxes above. [3] (ii) Suggest reagents and conditions for step 1, … step 2. … [3] (iii) What type of organic salt is formed in step 2? … [1]

13 9701/42/O/N/15 © UCLES 2015 [Turn over (b) Compound W has the following structure. NH2 H2N O (i) How many σ and π bonds are present in a molecule of W? σ bonds … π bonds … [2] (ii) The products of the reactions of W with cold HCl and with CH3CH2Br are soluble in water but not in organic solvents. Complete the table for these reactions of W. reagent structure of product (molecular formula given) type of reaction HCl (C4H9N2OCl ) CH3CH2Br (C6H13N2BrO) [3] [Total: 12]

14 9701/42/O/N/15 © UCLES 2015 Section B Answer all the questions in the spaces provided. 8 (a) The sequence of bases in DNA is a code for the order of amino acids in the primary structure of proteins. The diagram represents the stages involved in the formation of a protein from DNA. DNA ribosome protein A B2 B1 stage 1 etc. stage 3 stage 2 (i) Identify the biochemical structures, A and B1, B2 etc. biochemical structure identity A B1, B2 etc. [2] (ii) Name the biochemical processes involved in stages 1 and 3. process name of biochemical process stage 1 stage 3 [1]

15 9701/42/O/N/15 © UCLES 2015 [Turn over (b) Adenine is an integral part of DNA. N N N NH2 N H adenine (i) State the molecular formula of adenine. … [1] (ii) Identify the three other nitrogenous bases in DNA. … … … [1] (iii) DNA has a double helical structure that consists of two strands linked together. What type of bonding exists between the phosphate and sugar groups within a DNA strand, … different bases on the two strands? … [2] (c) The breakdown of adenosine triphosphate, ATP, provides the energy for many cellular reactions. ATP + H2O → ADP + Pi What type of chemical reaction is this? … [1] (d) X-ray crystallography can be useful in obtaining information about the structures of large organic molecules, such as ATP. The technique involves X-rays interacting with the electrons within the molecule. (i) Which element in the molecule of ATP will interact most strongly with the X-ray beam? … [1] (ii) Explain why X-ray crystallography will not detect hydrogen atoms. … … [1] [Total: 10]

16 9701/42/O/N/15 © UCLES 2015 9 (a) Some metals are essential to biochemical processes. Complete the following table naming one metal in each case. biochemical process metal haemoglobin in oxygen transport transmission of nerve impulses enzyme cofactor [2] (b) Enzymes are a special type of protein molecule that catalyse biochemical reactions. Explain briefly the mechanism by which an enzyme breaks down a substrate molecule. … … … … … [3] (c) Disulfide bonds play an important role in the stability of some proteins such as the keratin in human hair. The amino acid involved in the formation of a disulfide bond is cysteine, H2NCH(CH2SH)CO2H. (i) At which level of protein structure (primary, secondary, tertiary) are disulfide bonds formed? … [1] (ii) Use a functional group in cysteine to show how disulfide bonds are formed. [1] (iii) What type of chemical reaction is this? … [1]

17 9701/42/O/N/15 © UCLES 2015 [Turn over (d) The NMR spectrum of cysteine, H2NCH(CH2SH)CO2H, shows five absorptions. After shaking a solution of cysteine with a few drops of D2O, the NMR spectrum shows only two absorptions, E and F, shown below. E F (i) Identify the two types of protons responsible for the absorptions E and F. E … F… [1] (ii) State and explain the splitting patterns of the absorptions E and F. E … … F … … [2] [Total: 11]

18 9701/42/O/N/15 © UCLES 2015 10 (a) Aspartame is an artificial sweetener that has the structure shown below. aspartame OH O O O NH2 H3C N H O (i) Draw a circle around each chiral centre in aspartame. [1] In the stomach, aspartame is hydrolysed by acid to form three organic products. (ii) On the diagram above, use arrows to indicate the two bonds that would be hydrolysed in the stomach. [2] (iii) Draw the structures of the three products formed after complete acid hydrolysis of aspartame. [3]

19 9701/42/O/N/15 © UCLES 2015 [Turn over (b) Aspartame is soluble in water. By referring to the structure of aspartame, explain why it is soluble in water. … … … [2] (c) Recently, nanotechnology has been involved in the development of a new natural sweetener, Nano Sugar, extracted from sugar cane. What is the approximate width of a nanoparticle? … [1] [Total: 9]

20 9701/42/O/N/15 © UCLES 2015 BLANK PAGE 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.

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Level MARK SCHEME for the October/November 2015 series 9701 CHEMISTRY 9701/42 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 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 A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 1 (a) Ca 3s23p64s2 and Ca2+ 3s23p6 1 (b) Ca(OH)2 + 2HNO3 → Ca(NO3)2 + 2H2O or CaO + 2HNO3 → Ca(NO3)2 + H2O 1 (c) (i) CaO and brown gas 1 (ii) the (cat)ion size / radii increases decreasing its ability to polarise the nitrate ion / N-O bond 2 (d) (i) (energy change when) 1 mole of ions gaseous (ions) dissolve in water (to form an infinitely dilute solution) or gaseous (ions) form an aqueous solution 2 (ii) ∆Ho lattCa(NO3)2 + ∆Ho solCa(NO3)2 = ∆Ho hyd Ca2+ + 2∆Ho hyd NO3 – ∆Ho latt – 19 = –1650 + (2x –314) –2259 kJ mol–1 3 1 Ca(2+) is a smaller (ion) or Ca(2+) has a larger charge density Ca(2+) has a stronger attraction / bond to H2O 2 12

Page 3 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 2 (a) Na Mg Al Si P S Cl Ar 1 0 1 2 3 2 1 0 3 (b) (i) SiCl4 white solid / ppt or misty / white / steamy fumes pH 0–3 PCl5 misty / white / steamy fumes pH 0–3 3 (ii) SiCl4 + 2H2O → SiO2 + 4HCl 1 7

Page 4 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 3 (a) forms (one or more) ions with incomplete d orbital(s)/sub-shells/shells 1 (b) (i) dative (covalent) or co-ordinate 1 (ii) species can act as a ligand cannot act as a ligand NO3 -
BF3
H2NCH2CH2NH2
NH4 +
2 (c) (i) formula of manganese species formed type of reaction Mn2+ (aq) + NaOH (aq) Mn(OH)2 Mn(H2O)4(OH)2 Mn(OH)3 precipitation Mn2+ (aq) + concentrated HCl MnCl4 2– MnCl6 4– ligand exchange / substitution Mn2+ (aq) + aqueous H2O2 Mn3+ redox / oxidation 5 9

Page 5 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 4 (a) M1: dipole on C–Cl bond M2: curly arrow breaking C–Cl bond M3: curly arrow from the oxygen on -OH (lone pair needs to be shown) to carbon in C–Cl bond and Cl– (ion) formed in the mechanism 3 (b) (i) time taken for the concentration of a reactant(s) to fall to half its original value 1 (ii) evidence of a pair of construction lines on graph and t½ = 49–53 s 1 (iii) no effect / change 1 (c) (i) evidence of tangent at 80 s and data used, e.g. 0.42 / 152 = 0.00263 units mol dm–3 s–1 2 (ii) correct use of answer to (i)/0.19 and s-1 1 9 C H3C H3C H3C δ+ δ– -:OH C OH H3C H3C H3C + Cl Cl–

Page 6 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 5 (a) (i) M1: salt bridge and voltmeter / M2: method of H2 gas delivery M3: X and Pt electrode labelled M4: solution H+ / HCl(aq) / H2SO4 and X2+ labelled 4 (ii) 25 oC / 298 K and 1 atm / 101 kPa pressure and 1 mol dm–3 (solution) 1 (iii) solution – ions or H+ and X2+ and wires – electrons / e– 1 (b) (i) X + 2Ag+ → 2Ag + X2+ 1 (ii) moles Ag = 1.30 / 107.9 = 0.0120 1 moles of X react with 2 moles Ag+ moles of X lost = 0.012 × 0.5 = 0.00602 Ar of X = 0.67/0.006 = 111–112 and X = Cd 4 11

Page 7 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 6 (a) 4BF3 + 3NaBH4 → 2B2H6 + 3NaBF4 1 (b) 3 (c) (i) (electrophilic) addition 1 (ii) CH3 CH3 CH3 C H3 1 O :H δ+ δ− [1] intermediate (M3) [1] dipoles (M1) [1] both curly arrows (M2) arrow must come from lone pair – O–

Page 8 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks (d) (i) any four of M1: σ-bonds between C–C or C–H M2: π-bonds formed from overlap of p-orbitals M3: (π-bonds/electrons) above and below the ring M4:bonds/electrons are delocalised M5: bond angle 120° M6: intermediate C–C bond length / all C–C same length / strength M7: carbons are sp2 hybridised 3 (ii) correct delocalised structure of borazine 1 10 N B N B N B

Page 9 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 7 (a) (i) 3 (ii) Sn + HCl HNO2 or NaNO2 + HCl step 1 (linked to a reduction) reflux / heat / >50 oC or conc / 6M (HCl) and step 2 ⩽10 oC 3 (iii) diazonium (group) 1 (b) (i) σ-bonds = 14 π-bonds = 2 2 N T R NH2 SO3 –Na+ SO3 –Na+ N+ S OH Na+ –O3S

Page 10 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 7 reagent structure of product type of reaction HCl N H3 + NH2 O Cl- acid-base or neutralisation CH3CH2Br NH2 + NH2 O CH3CH2 Br- (nucleophilic) substitution 3 12

Page 11 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 8 (a) (i) A = mRNA B1 and B2, etc. = tRNA or tRNA-amino acid complex 2 (ii) stage 1 = transcription and stage 3= translation 1 (b) (i) C5H5N5 1 (ii) cytosine, thymine, guanine 1 (iii) covalent hydrogen bonding 2 (c) hydrolysis 1 (d) (i) Phosphorus / P 1 (ii) H atoms have insufficient electron density or electrons (to show up) or H atoms contain one e– 1 10

Page 12 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks 9 (a) iron / Fe (= haemoglobin) sodium / Na or potassium / K (= transmission of nerve impulses) Zn or Cu or Mg or Mn or Mo or Ni or Fe or Co (= enzyme co-factor) 2 (b) any three of: M1: substrate binds to / fits into the active site of the enzyme M2: Interaction with site causes a specific bond to be weakened, (which breaks) M3: lowers activation energy M4: products released from the enzyme/active site 3 (c) (i) Tertiary 1 (ii) 2 –SH → –S – S– (+ 2H) 1 (iii) oxidation 1 (d) (i) E = CH and F = CH2 1 (ii) E = triplet and adjacent 2H F = doublet and adjacent 1H 2 11 10 (a) (i) 1

Page 13 Mark Scheme Syllabus Paper Cambridge International A Level – October/November 2015 9701 42 © Cambridge International Examinations 2015 Question Marking point Marks (ii) 2 (iii) 3 (b) M1: hydrogen bonding M2: between the NH2 groups and water or CO2 / C=O / –OH groups and water (allow names) or lone pair on N/O with water 2 (c) allow range 1–200 nm or 1–200 × 10–9 m 1 9 O HO NH2 NH2 OH O O HO CH3-OH