MARK SCHEME for the October/November 2014 series 9701 CHEMISTRY

Transcription

1 CAMBRIDGE INTERNATINAL EXAMINATINS Cambridge International Advanced Level MARK SCEME for the ctober/november 204 series 970 CEMISTRY 970/43 Paper 4 (A2 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 ctober/november 204 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge Level components. IGCSE is the registered trademark of Cambridge International Examinations.

2 Page 2 Mark Schemee Cambridge International A Level ctober/november 2044 Syllabus 9709 Paper 433 Question Marking poinp nt Marks Marks total (a)) (i) m/em identity Cll Cll C Cl 35 Cl C or 35 Cl Cl C 35 Cl C 35, 37,, 70, 72, 744 correctt formulae at least one structure ass a positive ion Cl 37 Cl C or 37 Cl 2 (ii) 9:6: [4] (b)) (i) correct charges correct electrons (ii) Lattice energy = f (SrCl 2 ) ( atom( (Sr) + i ( Sr) + i2 (Sr) + = +( 830) ( ( )) = 246 (kj mol ) atom m(cl) + 2 ea (Cl)) [5] (c)) (i) SrC 3 + 2N 3 Sr(N 3 ) 2 + C Cambridgee International ExamE minations 204

3 Page 3 Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (ii) Sr(N 3 ) 2 Sr + 2N [2] (d) (down the group) nitrates become more stable / require a higher temperature to decompose as size/radius of ion increases R charge density of ion decreases so polarisation/distortion of anion/nitrate ion/n 3 /N bond decreases [3] 2 (a) Br 3 + 5Br Br five correct species correct balancing [2] (b) (i) [Br 3 ] st order and the concentration is x2, rate doubles R evidence using expt & 4 eg ratios [ + ] 2 nd order and the concentration is x2, rate x4 R evidence using expt & 2 [Br - ] st order and the concentration is x4, rate x4 R evidence using expt & 3 eg ratios (ii) (Rate =) k [Br 3 ][Br ][ + ] 2 (iii) k =.32 mol 3 dm 9 s [6] 3 (a) (i) chromium and copper (ii) (all orbitals have the) same energy (iii) correct id of one higher energy d orbital the other higher energy d orbital [4] Cambridge International Examinations 204

4 Page 4 Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (b) (i) pale blue precipitate A Cu() 2 R [Cu() 2 ( 2 ) 4 ] solution B [Cu(N 3 ) 4 ( 2 ) 2 ] 2+ R [Cu(N 3 ) 4 ] 2+ solution C [CuCl 4 ] 2 (ii) solution B royal / deep / dark blue R violet-blue solution C yellow / green (iii) redox R oxidation of Cu R reduction of Cu 2+ AND reducing agent / reductant [6] (c) (d) 3d-shell is full / 3d 0 / no vacant d-orbital / d-orbitals full electrons cannot move between orbitals R transitions cannot occur green / yellow orange / red AND blue / violet light is absorbed [2] [2] 4 (a) (Cl) stronger acid / more dissociated / ionised in solution (Cl has) more ions / higher concentration of ions (b) (i) A solution that resists changes in the p / keeps p fairly constant when small quantities / amounts / vols of acid / + or base / are added [2] (ii) add (ethanoic acid) to Na R an equation excess (ethanoic acid) R mix with sodium ethanoate [4] (c) C 3 C(N 2 )C + + C 3 C(N 3 + )C C 3 C(N 2 )C + C 3 C(N 2 )C + 2 [2] Cambridge International Examinations 204

5 Page 5 Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (d) (i) pka pka (ii) C (S,R) C C (R,S) C 2 [4] C (R,R) any two of the above C 5 (a) any five of these seven points. σ-bonds are between C-C R C- carbons are sp 2 rings of charge above and below the ring must be in diagram presence of σ-bonds electrons/bonds are delocalised planar molecule/bond angles 20 o all C-C are the same length/have intermediate bond length between C-C & C=C 5 [5] Cambridge International Examinations 204

6 Page 6 Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (b) Reagent X e.g. Br 2, N 3, Na, Na, benzenediazonium salt / ion; RCCl ; Fe 3+ ; 2 +Ni substituted product for L-DPA & vanillin (examples given are for X = Br 2 and Na) Br Br or - N 2 C N 2-3 C - 3 C 2 Reagent Y e.g. Cl; Na 2 C 3, Mg, SCl 2, PCl 5, R + c. 2 S 4 ; Cl+NaN 2 / N 2 ; C 3 Cl Correct substituted product for L-DPA N 3 + C Reagent Z e.g. acidified Cr ; 2,4-DNP, hydrazine ; Fehling s, Tollens ; CN; CN + NaCN; NaB 4 ; correct substituted product for vanillin [7] 6 (a) (i) C 5 2 N 2 Cambridge International Examinations 204

7 Page 7 Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (ii) C 3 NC 2 C 3 (iii) any two of ketone, amine or ether 2 [4] Cambridge International Examinations 204

8 Page 8 Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (b) (i) LiAl 4 C 3 reduction / nucleophilic addition (ii) Cl (aq) NC 2 C 3 C 3 acid-base / neutralisation + N 2 C 2 C 3 (Cl - ) (iii) C 3 CCl C 3 N acylation / condensation allow addition + elimination allow nucleophilic substitution 3 C 2 C CC 3 mark for each correct structure mark for each correct reaction type 3 3 [6] Cambridge International Examinations 204

9 Page 9 Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (a) (ratio of) the concentrations / distribution / amount / mass of solute in two (immiscible) solvents at equilibrium R equilibrium constant R includes expression with K (b) K pc = [J in ether]/[j in 2 ] = (2.4/20)/(5 2.4/75) =2.8 R 2.82 (c) st extraction: 2.8 =(x/0)/(5.0 x)/75 2.8(5 x) = 7.5x x=.36 g 2 nd extraction: 2.8 =(y/0)/(3.64 y)/75 2.8(3.64-y) = 7.5y y= 0.99 g [2] [2] [2] (d) (i) water / solvent / named solvent (ii) non-volatile liquid, for example mineral oil or at least a C 5 hydrocarbon oil (iii). R f (retardation factor) or distance travelled by solute and distance by solvent 2. retention time [4] Cambridge International Examinations 204

10 Page 0 Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (e) C 2 2 [] C 2 C 2 C (a) C = 33 % A = T = 7 % [2] (b) (i) only one isomer may be active / be of therapeutic benefit (ii) the other (stereo) isomer may cause harm / side effects [2] Cambridge International Examinations 204

11 Page Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (c) (i) structures of the following aldehydes: C C C C two correct structures = mark two further correct structures mark (ii) 3-methylbutanal (iii) pentanal 5 absorptions 2-methylbutanal 5 absorptions dimethylpropanal 2 absorptions [6] 9 (a) nylon, terylene condensation; PVC addition all three correct [] (b) correct fully displayed formula of -C-N- unit correct polymer structure [2] N C N C N C N C (c) sequence / order of amino acids (in the polypeptide chain) [] (d) hydrogen bond C= and N- in two different amino acids in the backbone diagram Cambridge International Examinations 204 [2]

12 Page 2 Mark Scheme Syllabus Paper Cambridge International A Level ctober/november (e) (i) (ii) disrupts hydrogen/ionic bonds as C/N 3 + is deprotonated R N N linked to hydrogen / ionic bond disrupted R C + C + 2 linked to hydrogen / ionic bond disrupted g 2+ interferes with/breaks the disulfide bond / bridge not sulfite, sulfate, sulfur, sulfide R -S-S- shown with g 2+ in an equation R disrupting ionic interactions linked to carboxyl / C groups (iii) (eat to 70 C) breaks the van der Waals forces / hydrogen bonding [3] Cambridge International Examinations 204