CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Level MARK SCHEME for the October/November 05 series 970 CHEMISTRY 970/43 Paper 4 (A Structured Questions), maximum raw mark 00 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 05 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.
Page Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 (a) ionic bonds break / bonds between Mg + and Cl - break forces / bonds / attractions form between the ions and water (b) (i) (the energy change) when mole of a substance dissolves in water / becomes aq H o latt MgCl + H o sol MgCl = H o hyd Mg + + H o lhyd Cl 54 55 = 95 + H o hyd Cl - = 377 kj mol (iii) magnesium / Mg is higher charge / sodium / Na is smaller charge magnesium / Mg is smaller / sodium / Na is larger Mg stronger attraction for water / Na weaker attraction for water any two (c) solubility decreases lattice energy and hydration enthalpy decrease hydration enthalpy decreases more rapidly / is dominant factor so (enthalpy change of) solution becomes less exothermic / more endothermic 4 [Total: ] (a) Co 3s 3p 6 3d 7 4s [] Co 3+ 3s 3p 6 3d 6 [] (b) (i) atom or ion, bonded to (one or more), ligands any two from: two (or more) oxidation states, catalytic activity, coloured ions or compounds Cambridge International Examinations 05
Page 3 Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 (c) transition element species formed type of reaction 5 Co + (aq) + an excess of NH 3 (aq) Co + (aq) + OH (aq) Co + (aq) + S O 8 (aq) [Co(NH 3 ) 6 ] + or [Co(NH 3 ) 4 ] + or [Co(NH 3 ) 4 (H O) ] + Co(OH) or Co(OH) (H O) 4 [Co(H O) 6 ] 3+ or Co 3+ or Co (SO 4 ) 3 ligand exchange precipitation or acid-base redox or oxidation or reduction of S O 8 (d) (i) Y 3.4 / 88.9 or 0.5 Ba 4. / 37 or 0.3 Cu 8.6 / 63.5 or 0.45 O 6.8 / 6 or = 7 / 3 or (+).3 (iii) two Cu are + and one Cu is + 3 [Total: 3] Cambridge International Examinations 05
Page 4 Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 3 (a) (i) Fe + and Fe 3+ (or suitable compounds), or 3 marking points = [] salt bridge labelled, 4 or 5 marking points = [] one electrode Pt labelled, 6 or 7 marking points = [3] one sol n mol dm 3 8 marking points = [4] Cl (or suitable compound), voltmeter, labelled or V Cl, atm or 98K 4 + 3+ - E o cell =.36 0.77 = 0.59 V (b) yellow / orange / brown (c) cell voltage increases or becomes more positive Cl / Cl electrode potential increases Cambridge International Examinations 05
Page 5 Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 (d) (i) H + OH H O + e O + H O + 4e 4OH H + O H O (iii) rechargeable / refillable / longer time between charges / longer battery life / less pollution because H O is the product / O can be got from the air [Total: ] 4 (a) (i) sketch graph to show a general decrease in m.p giant covalent (C or Si) to metal / metallic (Sn or Pb) (b) (i) (c) (i) can react with an acid or base / alkali or can act as an acid or base or has acidic and basic properties SnO + NaOH Na SnO 3 + H O or SnO + NaOH + H O Na Sn(OH) 6 E o cell = +.8 or E o Cr O 7 greater / more positive than Sn 4+ or E o (Cr O 7 / Cr 3+ ) +.33 and E o (Sn 4+ / Sn + ) + 0.5 Cr O 7 + 3Sn + + 4H + Cr 3+ + 3Sn 4+ + 7H O green (d) (i) the same substance gets both oxidised and reduced in the reaction or Ge changes oxid. no. + to 0 and changes oxid. no. + to + 4 (CN) + NaOH NaOCN / NaCNO + NaCN + H O Cambridge International Examinations 05
Page 6 Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 (iii) (e) (i) P : P P = 489 = 978 kj mol and P 4 : 6 P P = 6 98 = 88 kj mol H = 978 88 = 0 kj mol (f) (i) 3NH 4 Cl + 3PCl 5 HCl + P 3 N 3 Cl 6 Cl Cl P Cl N P N P Cl Cl N Cl or N Cl P Cl Cl P N N P Cl Cl Cl [Total: 5] 5 (a) (i) L,4-DNPH or Brady s reagent or LiA l H 4 or NaBH 4 M Fehling s solution or Tollens reagent or acidified K Cr O 7 or MnO 4 N alkaline I 3 CH 3 CH CH CO Na or CH 3 CH CH CO Na + or CH 3 CH CH CO H Cambridge International Examinations 05
Page 7 Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 (iii) yellow precipitate (iv) redox or oxidation (b) (i) 3 two curly arrows [] dipole [] intermediate [] Li CH 3 CH 3 [Total: 0] Cambridge International Examinations 05
Page 8 Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 6 (a) reagent organic product non-organic product 4 Na O N ONa H / hydrogen Br (aq) Br HBr O N OH Br or 3 Br s any position CH 3 COCl (l) O N OCOCH 3 HCl (b) (i) H N NH H N NH H N SO 3 - Na + N N + SO 3 - Na + E F Cambridge International Examinations 05
Page 9 Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 (b) step : NaNO + HCl or HNO 3 step : T 0 º C step : alkaline or NaOH(aq) or NaOH solution [Total: 9] 7 (a) backbone of sugar-phosphate-sugar-phosphate base bonded to sugar deoxyribose correct label two complementary base pairings e.g A T or C G hydrogen bonding / H bonding between bases, labelled 5 (b) any two of DNA uncoils or unzips hydrogen bonds break or weaken complementary bases join to form a new strand of DNA Cambridge International Examinations 05
Page 0 Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 (c) (i) restriction enzymes electrophoresis (iii) radioactive substance (iv) suspect 3 [Total: ] 8 (a) (i) time taken for a compound to travel through the column hydrogen or helium or nitrogen (iii) it is more soluble in the stationary phase (iv) same functional group or same IMF with stationary phase or same polarity (v) % X (= 00 / 76) = 9 (8.9) (b) (i) TMS or tetramethylsilane or Si(CH 3 ) 4 Cambridge International Examinations 05
Page Mark Scheme Syllabus Paper Cambridge International A Level October/November 05 970 43 4 chemical shift δ / ppm type of proton(s) number of protons splitting pattern.0 CH 3 -R 3 triplet.3 CH CO quartet 3.7 CH 3 O 3 singlet (iii) structure / name of methyl propanoate O H 3 C C CH 3 CH O [Total: ] 9 (a) C 4 (H 34 )N O 3 (b) ketone amine ester Cambridge International Examinations 05
Page Mark Schemee Cambridge International A Level October/November 055 Syllabus 9709 PapP per 433 Question Markingg Point Markss Totall Markss (c) (i) (d) hydrogen bondingg or ion-dipole forces involving lone pairr on N atoma ms, or lone pair onn O atoms, or NHN groups, orr CO groups, or C=O groups, withh water [Total: 8] Cambridgee International ExamE minations 05