MARK SCHEME for the October/November 2013 series 9701 CHEMISTRY

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1 CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Level MARK SCHEME for the October/November 2013 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 2013 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

2 1 (a) Page 2 Mark Scheme Syllabus Paper 8 e - around chlorine 1 H electron (+) on the Cl - ion 3 covalent (ox) and one dative (oo) around N (b) (i) it would react (with H 2 SO 4 ) (ii) CaO + H 2 O Ca(OH) 2 (iii) CaO absorbs more water or CaO has greater affinity for water (c) (i) 2Ca(NO 3 ) 2 2CaO + 4NO 2 + O 2 (ii) (Down the group, the nitrates) become more stable/stability increases because the size/radius of ion (M 2+ ) increases thus causing less polarisation/distortion of the anion/no 3 - /N-O bond [Total: 10]

3 Page 3 Mark Scheme Syllabus Paper 2 (a) (i) Si-Si bonds are weaker (than C-C bonds) (ii) metallic (Sn) is weaker than (giant) covalent (Ge) (b) (i) SiCl 4 + 2H 2 O SiO 2 + 4HCl or SiCl 4 + 4H 2 0 Si(OH) 4 + 4HCl or SiCl 4 + 3H 2 0 H 2 SiO 3 + 4HCl (partial hydrolysis is not sufficient e.g. to SiCl 3 OH + HCl) (ii) PbCl 4 PbCl 2 + Cl 2 (iii) SnCl 2 + 2FeCl 3 SnCl 4 + 2FeCl 2 (iv) SnO 2 + 2NaOH Na 2 SnO 3 + H 2 O or SnO 2 + 2NaOH + 2H 2 O Na 2 Sn(OH) 6 or ionic equation SnO 2 + 2OH - SnO H 2 O [Total: 6]

4 Page 4 Mark Scheme Syllabus Paper 3 (a) (i) NH 3 + HZ NH Z - CH 3 OH + HZ CH 3 OH Z - (ii) NH 3 + B - - NH 2 + BH CH 3 OH + B - CH 3 O - + BH (b) (i) a reaction that can go in either direction (ii) rate of forward = rate of backward reaction or forward/back reactions occurring but concentrations of all species do not change (c) (i) a solution that resists changes in ph when small quantities of acid or base/alkali are added (ii) in the equilibrium system HZ + H 2 O Z - + H 3 O + addition of acid: reaction moves to the left or H + combines with Z - and forms HZ addition of base: the reaction moves to the right or H + combines with OH - and more Z - formed [5 max 4] (d) (i) [H + ] = ( ) = (mol dm -3 ) ph = 2.59/2.6 (min 1 d.p) ecf (ii) CH 3 CH 2 CO 2 H + NaOH CH 3 CH 2 CO 2 Na + H 2 O (iii) n(acid) in 100 cm 3 = /1000 = 0.05 mol n(acid) remaining = = 0.02 mol [acid remaining] = 0.2 (mol dm -3 ) likewise, n(salt) = 0.03 mol [salt] (mol dm -3 ) (iv) ph = log(0.3/0.2) = ecf [6] (e) G is CH 3 CH 2 COCl H is SOCl 2 or PCl 5 J is NaCl (or corresponding Br compounds for G, H and J; CH 3 CH 2 COBr, SOBr 2, NaBr) [Total: 18]

5 Page 5 Mark Scheme Syllabus Paper 4 (a) (the energy change) when 1 mol of bonds is broken in the gas phase (b) (i) (C-X bond energy) decreases/becomes weaker (from F to I) due to bond becoming longer/not such efficient orbital overlap (ii) (as the bond energy of C-X decreases) the halogenalkanes become more reactive (answer must imply that it is from F to I) (c) The C-Cl bond is weaker than the C-F and C-H bonds or C-Cl bond (E = 340) and C-H (E = 410) so is (easily) broken to form Cl /Cl radicals/cl atoms causing the breakdown of O 3 into O 2 (d) Cl-CH 2 CH 2 -CO 2 H HO-CH 2 CH 2 CH 2 -Cl OH Br (e) (i) light/uv/hν or 300 C (ii) (free) radical substitution (iii) H = E(C-H) E(H-Cl) = = 21 kj mol -1 (iv) H = E(C-H) E(H-I) = = +111 kj mol -1 ecf (v) The reaction with iodine is endothermic or H is positive or requires energy (vi) Cl 2 2Cl CH 3 CH 2 + Cl 2 CH 3 CH 2 Cl + Cl CH 3 CH 2 + Cl CH 3 CH 2 Cl [8] [Total: 19]

6 Page 6 Mark Scheme Syllabus Paper 5 (a) (i) many monomers form a polymer (ii) addition (iii) C=C/double/π bond is broken and new C-C single bonds are formed or double bond breaks and forms single bonds with other monomers (b) propenoic acid (c) (i) carbon chain and CO 2 H at least one sodium salt (ii) 120 to 109(.5) due to the change from a trigonal/sp 2 carbon to a tetrahedral/sp 3 carbon (d) (i) Any four: hydrogen bond labelled water H-bonded to O through H atom δ+/δ- shown on each end of a H-bond lone pair shown on O - or C=O or H 2 O on a correct H-bond Na + shown as coordinated to a water molecule (ii) Solution became paler and Cu (2+) swapped with Na (+) or darker in colour and polymer absorbs water

7 Page 7 Mark Scheme Syllabus Paper (e) (i) alkene(1), amide(1) (ii) NH 3 (iii) H 2 O (iv) HCl (aq)/h 3 O + and heat/reflux (not warm) or OH - (aq), heat and acidify [5] [Total: 17]

8 Page 8 Mark Scheme Syllabus Paper Section B 6 (a) (i) six/6 (gsv, sgv, gvs, vgs, svg,vsg) (ii) two displayed peptide bonds correct formula of peptide (iii) valine (allow glycine) (iv) any two of: hydrogen bonds and CO 2 H or OH or NH 2 or CONH or CO or NH or CO 2 - ionic bonds and NH 3 + or CO 2 van der Waals and CH 3 or H 2 [6] (b) (i) same shape/structure as substrate (inhibitor) competes/blocks/binds/bonds to active site or substrate cannot bind to active site (ii) binds with enzyme and changes shape/3d structure (of enzyme/active site) (iii) [Total: 10]

9 Page 9 Mark Schemee GCEE A LEVELL October/ /November 2013 Syllabus 9701 Paper 42 7 (a) powerr supply (ideaa of completee circuit) electrolyte/ /buffer solus ution gel/ /filter paper/absorbent paper ( aminoo acid) sample/ /mixturee [centre of plate] 4 (b) anyy two from: size/mm r (of the amino acid species) chargee ( on the amino acid species) temperature 2 (c) Ratio of the concentration off a solute in each of two ( immiscible) solvents or equilibrium constant representing the distribution of a solute between two solvents or PC = [X] a /[X] b (at a constant temperature) (d) (i) K pc = [Z in ether] ]/[Z in H2O] allow reverse ratio 400 = (x/0.05)/((4 x)/0.5)) = 3. 2 g ecf (ii) First extractionn 400 = (x/0.025)/((4 x)/ 0.5) x = 2.67 g ecf (iii) Second extraction: 1. 33g remr main in solution Second extraction 400 = (y/0.025)/(( 1.33 y)/0. 5) y = g masm ss extracted = = 3..56/3.6 g ecf [Total: 11] Cambridge International Examinations 2013

10 Page 10 Mark Scheme Syllabus Paper 8 (a) (i) (nitrates are) soluble (ii) Ba (2+) and Pb (2+) SO 4 (2-) BaCO 3 /PbCO 3 /CaSO 4 are insoluble (b) (i) fertilisers/animal manure (ii) washing powder/detergents/fertilisers/animal manure (iii) growth/production of algae/weeds/plants or eutrophication (c) (i) any one of: 2SO 2 + O 2 2SO 3 and SO 3 + H 2 O H 2 SO 4 or SO 2 + NO 2 SO 3 + NO and SO 3 + H 2 O H 2 SO 4 or SO 2 + ½O 2 + H 2 O H 2 SO 4 (ii) roasting sulfide ores/extraction of metals from sulfide ores [Total: 9]

MARK SCHEME for the October/November 2015 series 9701 CHEMISTRY

CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Level MARK SCHEME for the October/November 015 series 9701 CHEMISTRY 9701/4 Paper 4 (A Structured Questions), maximum raw mark 100