MARK SCHEME for the May/June 2011 question paper for the guidance of teachers 9701 CHEMISTRY

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1 UNIVERSITY F CAMBRIDGE INTERNATINAL EXAMINATINS GCE Advanced Level MARK SCHEME for the May/June 2011 question paper for the guidance of teachers 9701 CHEMISTRY 9701/41 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 must be read in conjunction with the question papers and the report on the examination. Cambridge will not enter into discussions or correspondence in connection with these mark schemes. Cambridge is publishing the mark schemes for the May/June 2011 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some rdinary Level syllabuses.

2 Page 2 Mark Scheme: Teachers version Syllabus Paper 1 (a) N N triple bond is (very) strong or the N 2 molecule has no polarity (b) 3Mg(s) 3Mg 2+ (g) H 1 = = 7002 N 2 (g) 2N 3 (g) H 2 = = 5290 LE = H 1 H = 12,753 (kj mol 1 ) ( for each error) [3] (c) (i) Li 3 N + 3H 2 NH 3 + 3LiH (balanced equation) (ii) advantage: no high pressure/temperature/catalyst needed/standard conditions used disadvantage: Li is expensive or Li would need to be recycled/removed or LiH by-product is corrosive/strongly basic or this would be a batch, rather than continuous process (d) (i) Li 3 N: /35 = 40% N urea: /60 = 47% N (ii) amide (iii) NH 2 CNH 2 + H 2 2NH 3 + C 2 or NH 2 + NH 3 or NH 2 CNH 2 + 2H 2 2NH 3 + H 2 C 3 (iv) The LiH would be strongly alkaline or would increase the ph of the soil or would burn the crops/reduce plant growth/stunt plants or would contaminate the environment [Total: 12]

3 Page 3 Mark Scheme: Teachers version Syllabus Paper 2 (a) (i) ne that can go in either direction. (ii) both forward & reverse reactions are going on at the same time, but the concentrations of all species do not change (owtte) or rate of forward = rate of backward reaction (b) (i) K c = [H + ][H ]/[H 2 ] (ii) K w = [H + ][H ] rearrangement of equation in (i) gives K c [H 2 ] = [H + ][H ] & K w = K c [H 2 ] (owtte) or the [H 2 ] is contained within K w (iii) K w will be higher in hot water because reaction is endothermic (c) (i) [H ] = ; [H + ] = ( )/ = ph = log 10 [H + ] = 12.7 (correct ans = [2]) ecf (ii) [NH 4 + ] = [H ] (= x) x 2 = x (= [H ]) = (mol dm 3 ) (correct ans = [2]) (iii) [H + ] = K w /[H ] = ( )/ = (mol dm 3 ) ecf (iv) ph = 11.0 ecf [Total: 12 max 11] 3 (a) (+)1; (+)2; (+)3; (+)4.N. corresponds to the no. of electrons in outer/valence shell/lost (b) PCl 5 fizzes or white/misty fumes or heat evolved PCl 5 + 4H 2 H 3 P 4 + 5HCl or PCl 5 + 3H 2 HP 3 + 5HCl (allow partial hydrolysis: PCl 5 + H 2 PCl 3 + 2HCl) (c) (i) P = 30.4/31 = 0.98 Cl = 69.6/35.5 = 1.96 Thus E.F = PCl 2 M r (PCl 2 ) = 102, so 2 PCl 2 = , so M.F. = P 2 Cl 4 (ii) Cl P P Cl (ignore lone pairs on Cl) Cl Cl (iii).n. = (+)2 (iv) (H) 2 P-P(H) 2 or H(H)P(=)-P(=)(H)H ecf from structure in (ii) Allow H-P-H or H-P= H [Total: 10]

4 Page 4 Mark Scheme: Teachers version Syllabus Paper 4 (a) N N 2 (or via N) or 2N + 2 2N 2 (b) (i) catalytic converter and passing the exhaust gases over a catalyst/pt/rh (ii) N 2 + 2C ½ N 2 + 2C 2 or similar Allow 2N 2 + CH 4 C 2 + N 2 + 2H 2 (c) No, it wouldn t be reduced. Because the reaction in (a) does not presuppose a particular fuel (owtte) Allow formed from N 2 and 2 in air during combustion (d) (i) S 3 produces acid rain (ii) N + ½ 2 N 2 (iii) K p = ( p N.p S3 )/( p N.p 2 S 2 ) units: dimensionless/none (don t accept just a blank!) (iv) K p = /0.2 2 = (v) It will shift to the right (owtte) because the reaction is exothermic. NT just Le Chatelier argument [Total: 11] 5 (a) transformation C 2 H 4 C 2 H 5 Cl C 2 H 5 H C 2 H 5 Cl C 2 H 6 C 2 H 5 Cl C 2 H 4 C 2 H 4 Cl 2 CH 3 CH 3 CCl reagent + conditions HCl, no light or catalyst conc HCl + ZnCl 2 or SCl 2 or PCl 5 or PCl 3 and heat Cl 2 + light Cl 2, no light or catalyst SCl 2 or PCl 5 or PCl 3 and heat H 3 C H 3 C Cl Cl 2 + AlCl 3 CH 3 CH 2 Cl Cl 2 + light or heat [6]

5 Page 5 Mark Scheme: Teachers version Syllabus Paper (b) (i) production of N + 2 : 2H 2 S 4 + HN 3 2HS 4 + H N 2 (accept H 2 S 4 + HN 3 HS 4 + H 2 + N + 2 ) N 2 H N 2 curly arrow from ring to N 2 + and from C-H bond to ring correct intermediate, including charge in the right place Note charge area must be more than half ring (ii) C is C 6 H 5 (iii) step 1: reagent is hot acidified or alkaline KMn 4 step 2: reagent is Br 2 + FeBr 3 /AlCl 3 etc. (H 2 or light negates) (If C is given as 3-bromotoluene, then allow the last [2] marks if steps 1 and 2 are reversed.) [Total: 12] 6 (a) (i) aqueous alkaline iodine or I 2 + H (aq) allow NaCl + KI (ii) CH 3 C- or CH 3 CH(H)- (iii) Pale yellow ppt. or antiseptic smell (iv) compound CH 3 H CH 3 CH 2 H CH 3 CH CH 3 result CH CCH 3 [3]

6 Page 6 Mark Scheme: Teachers version Syllabus Paper (b) (allow displayed, skeletal or structural formulae) CH + for D allow D E F (no mark for ) CH (D + E + F): 3 (c) (allow displayed, skeletal and structural formulae) Must be consistent with F H G H J (only allow mark for H allow for G if G is the 3-H acid) K H (N.B. letters H, J, K can be swapped around) (G + H + J + K): 4 geometrical or cis-trans isomerism [Total: 14]

7 Page 7 Mark Scheme: Teachers version Syllabus Paper 7 (a) The tertiary/3-dimensional structure/shape is held together by hydrogen/ionic/van der Waals bonds These break (relatively) easily/are weak/break at/above 45 C (b) (or similar diagrams) Enzyme + substrate Enzyme-substrate complex Enzyme + products 3 (c) a competitive inhibitor combines with the enzyme s active site (so preventing the substrate from binding) non-competitive inhibitor bonds with the enzyme away from the active site/at an allosteric site this changes the shape of the active site Also allow competitive inhibition can be overcome by increasing [substrate] or non-competitive inhibition cannot be removed by increasing [substrate] for the 3rd mark (d) (i) Line must be of similar shape to original but level out below original line (ii) Inhibitor reduces the number of enzymes with working active sites (owtte) [Total: 10]

8 Page 8 Mark Scheme: Teachers version Syllabus Paper 8 (a) partition separation due to the different solubilities of compounds in two solvents/phases adsorption separation due to the different attractions between the compounds and the stationary phase, relative to their solubility in the solvent Note, if candidates do not refer to different solubilities and different attractions max 1 (b) A B X - sample Ring: A + B: (c) (i) X is bromine M and (M+2) peaks almost same height (ii) M = = M n n Hence n = = 3.03 p = (answer + working) (If the mass peak is at 122 and the compound contains Br and 3 C atoms then Q = ( )) thus Q = 7 ecf from (ii) (The compound is C 3 H 7 Br) (iii) (R is at m/e 43), hence C 3 H 7 + (d) Any two from H 2, H 2, C, C 2 H 4, C 2 H 2, CH 4 2 [Total: 10]

9 Page 9 Mark Scheme: Teachers version Syllabus Paper 9 (a) (i) ne (ii) Any alkene (or allow a cyclic amide, as in caprolactam) (b) Any TW from: addition needs unsaturated/double bonds/alkene condensation eliminates a small molecule condensation needs a molecule other than a hydrocarbon empirical formula of addition polymer is the same as that of its monomer condensation needs two different functional groups (NT condensation needs two different monomers ) 2 (c) (i) Water (ii) CH 2 CH 2 Correct ester bond sticks to rest of molecule Note : candidates need only show brackets if more than one repeat unit shown (iii) Polyesters (d) Monomers in Terylene have to alternate in order to condense out water (owtte) Alkenes can link in any order (and still form a polyalkene) (or diagram showing this) [Total: 10]

9701 CHEMISTRY. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers.

9701 CHEMISTRY. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. CAMBRIDGE INTERNATINAL EXAMINATINS GCE Advanced Level MARK SCHEME f the May/June 04 series 970 CHEMISTRY 970/4 Paper 4 (Structured Questions), maximum raw mark 00 This mark scheme is published as an aid