Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level. Published

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1 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level CHEMISTRY 970/43 Paper 4 A Level Structured s October/November 06 MARK SCHEME Maximum : 00 Published 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. 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 06 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. This document consists of 7 printed pages. UCLES 06 [Turn over

2 Page Scheme Syllabus Paper Cambridge International AS/A Level October/November (a) Cu [Ar] 3d 0 4s Cu + [Ar] 3d 9 (4s o ) (b)(i) ligand exchange / replacement / displacement / substitution (b)(ii) [Cu(H O) 6 ] + blue and [CuCl 4 ] yellow OR yellow / green OR green / yellow (b)(iii) tetrahedral (b)(iv) K stab = [CuCl 4 ] / [Cu(H O) + 6 ][Cl ] 4 (c)(i) a species that contains two lone pairs that (each) form a co-ordinate / dative bond OR are donated (to a metal ion / atom) (c)(ii) equilibrium lies more to the RHS / favours forward reaction more (d)(i) optical (d)(ii) 3D correct for octahedral one correct structure with 3D second correct with 3D UCLES 06

3 Page 3 Scheme Syllabus Paper Cambridge International AS/A Level October/November (e)(i) (e)(ii) lone pair receive / accepts a proton / H + H NCH CH NH + HCl ClH 3 NCH CH NH 3 Cl OR H NCH CH NH + H + H 3 N + CH CH N + H 3 3 (f)(i) amide bond, displayed or CONH rest of the molecule with continuation bonds O O H N N H H N N H O O (f)(ii) condensation / addition elimination (f)(iii) any named polyalkene / eg polyethene, PVC allow Bakelite or Kevlar Total: 0 UCLES 06

4 Page 4 Scheme Syllabus Paper Cambridge International AS/A Level October/November (a) solid remains (b) stability increases (down the group) as size / radius of (metal) ion / M + increases so polarisation / distortion of anion / carbonate ion decreases 3 (c)(i) (c)(ii) CaCN + 3H O CaCO 3 + NH 3 CaCO 3 correct equation Total: 8 UCLES 06

5 Page 5 Scheme Syllabus Paper Cambridge International AS/A Level October/November (a)(i) (entropy) increases / is positive and H / gas is formed 3(a)(ii) (entropy) increases / is positive and (KCl (aq)) solution has (free) moving / mobile ions / aqueous ions 3(a)(iii) (entropy) decreases / is negative and decrease in gas 3(b)(i) S o = = (+) 75. (J K mol ) G o = 7 ( / 000) OR G o = (98 75.) G o = (kj mol ) 3 3(b)(ii) T S is more positive than H / T S increases / T S more negative and G is negative / decrease / less positive 3(c) use of G = 0 or T S = H T = 30 / (36 / 000) = 40 / 4 / 4 / 4.4 (K) UCLES 06

6 Page 6 Scheme Syllabus Paper Cambridge International AS/A Level October/November (d) hydration enthalpy and lattice energy both more endothermic / more positive / less exothermic / less negative (down the group) H hyd decreases more / faster and H sol becomes (more) endothermic / (more) positive / less exothermic / less negative Total: 4(a) (an element) forming one or more (stable) ions or compounds or oxidation states with partially filled / incomplete d orbitals 4(b)(i) A Co(OH) OR Co(H O) 4 (OH) B [CoCl 4 ] C [Co(NH 3 ) 6 ] + OR [Co(NH 3 ) 6 ] 3+ two correct = mark three correct = marks 4(b)(ii) [Co(H O) 6 ] + pink solution of B blue solution of C brown/yellow/orange UCLES 06

7 Page 7 Scheme Syllabus Paper Cambridge International AS/A Level October/November two correct = mark three correct = marks UCLES 06

8 Page 8 Scheme Syllabus Paper Cambridge International AS/A Level October/November (c) (emf / potential / E) of an electrode OR a half-cell compared to / connected to (S)HE which can be called a hydrogen half-cell at concentration of mol dm 3 and pressure of atm (or in Pa) OR 98 K 4(d)(i) half-cell electrode Co + / Co Co / cobalt Fe 3+ / Fe + Pt / carbon / graphite 4(d)(ii) Co + Fe 3+ Co + + Fe + 4(d)(iii) E o cell = 0.77 ( 0.8) = (+ or ).05 (V) 4(e)(i) E electrode = (0.059 / ) log [0.05] = 0.3 / 0.38 (V) 4(e)(ii) more positive 4(f) 4Fe 3+ + V + H O VO + + 4Fe + + H + VO + correct equation UCLES 06

9 Page 9 Scheme Syllabus Paper Cambridge International AS/A Level October/November Total: 4 UCLES 06

10 Page 0 Scheme Syllabus Paper Cambridge International AS/A Level October/November (a)(i) (00 /.) (0.7 /.) or.. 3 carbon atoms or.87 /.88 /.9 5(a)(ii) C 3 H 6 O 3 5(b) absorption / cm appearance of the peak type of bond functional group 3350 broad and strong OH or O H alcohol / ROH 680 very broad and strong OH or O H (carboxylic) acid / CO H 75 strong C = O (carboxylic) acid / CO H UCLES 06

11 Page Scheme Syllabus Paper Cambridge International AS/A Level October/November (c)(i) δ/ppm type of proton relative peak area.4 CH 3 or CH or CH or alkane OCH or OCH or OCH 3 or CH or alkyl next to electronegative atom / oxygen 4.7 OH or alcohol.9 OH or CO H or carboxylic acid 4 5(c)(ii) doublet and / one H / proton on neighbouring OR adjacent carbon 5(c)(iii) 4.7 and.9 OR OH and CO H 5(c)(iv) 5(d)(i) both required for mark UCLES 06

12 Page Scheme Syllabus Paper Cambridge International AS/A Level October/November (d)(ii) isomer number of peaks P 4 Q 4 Total: 5 6(a) ibuprofen: carboxylic acid / carboxyl paracetamol: phenol and amide any two = mark all three = marks 6(b)(i) (chiral centre is a) carbon OR atom that has four different groups / atoms / species attached to it UCLES 06

13 Page 3 Scheme Syllabus Paper Cambridge International AS/A Level October/November (b)(ii) one correct isomer second diagram shows second isomer 6(c) with ibuprofen with paracetamol UCLES 06

14 Page 4 Scheme Syllabus Paper Cambridge International AS/A Level October/November (d)(i) (reagent D) Na CO 3 / any carbonate (reagent E) Cl / Br 6(d)(ii) 6(d)(iii) 6(e)(i) CH 3 COCl + AlCl 3 CH 3 CO + + AlCl 4 UCLES 06

15 Page 5 Scheme Syllabus Paper Cambridge International AS/A Level October/November (e)(ii) curly arrow from ring system to CH 3 CO + correct intermediate curly arrow from C H bond into ring 3 6(e)(iii) electrophilic substitution Total: 6 UCLES 06

16 Page 6 Scheme Syllabus Paper Cambridge International AS/A Level October/November (a) moles of thiosulfate = / 000 = moles of ClO in 5 cm 3 portion = / = (moles of ClO in 50 cm 3 =.04 0 ) concentration of ClO =.04 0 / (0 / 000) =.04 (mol dm 3 ) 3 7(b)(i) starch 7(b)(ii) blue OR black to colourless 7(b)(iii) towards / close to the end-point of the titration / when the solution goes yellow 7(c) moles of O = 8 / = = moles ClO ions concentration of ClO = / (5 / 000) = 0.68 / / (mol dm 3 ) 7(d)(i) [C3H3N3O 3][HClO 3] K c = 3 [C Cl N O ][H 0] (d)(ii) (position of eqm) moves to the right / forward reaction predominates / more HClO made (as [HClO] decreases) no effect on K c UCLES 06

17 Page 7 Scheme Syllabus Paper Cambridge International AS/A Level October/November (d)(iii) HClO HCl + O OR HClO H + Cl + O 7(e)(i) addition of acid: H + + HCO 3 H CO 3 OR H + + HCO 3 H O + CO addition of base: OH + H CO 3 HCO 3 + H O OR H + + OH H O and position of eqm moves to the right OR OH + HCO 3 CO 3 + H O 7(e)(ii) K a = ([H + ][HCO 3 ] / [H CO 3 ]) [H + ] = ( ) / 9.5 = ph = log[h + ] = 7.08 Total: 6 UCLES 06