klm Mark Scheme Chemistry 6421 General Certificate of Education Further Physical and Organic Chemistry 2010 examination - January series

Transcription

1 2 nd February 200 klm General Certificate of Education Chemistry 642 CHM4 Further Physical and Organic Chemistry Mark Scheme 200 examination - January series

2 Mark schemes are prepared by the Principal Examiner and considered, together with the relevant questions, by a panel of subject teachers. This mark scheme includes any amendments made at the standardisation meeting attended by all examiners and is the scheme which was used by them in this examination. The standardisation meeting ensures that the mark scheme covers the candidates responses to questions and that every examiner understands and applies it in the same correct way. As preparation for the standardisation meeting each examiner analyses a number of candidates scripts: alternative answers not already covered by the mark scheme are discussed at the meeting and legislated for. If, after this meeting, examiners encounter unusual answers which have not been discussed at the meeting they are required to refer these to the Principal Examiner. It must be stressed that a mark scheme is a working document, in many cases further developed and expanded on the basis of candidates reactions to a particular paper. Assumptions about future mark schemes on the basis of one year s document should be avoided; whilst the guiding principles of assessment remain constant, details will change, depending on the content of a particular examination paper. Further copies of this Mark Scheme are available to download from the AQA Website: Copyright 2009 AQA and its licensors. All rights reserved. COPYRIGHT AQA retains the copyright on all its publications. However, registered centres for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to centres to photocopy any material that is acknowledged to a third party even for internal use within the centre. Set and published by the Assessment and Qualifications Alliance. The Assessment and Qualifications Alliance (AQA) is a company limited by guarantee registered in England and Wales (company number ) and a registered charity (registered charity number ). Registered address: AQA, Devas Street, Manchester M5 6EX Dr Michael Cresswell Director General

3 Chemistry - AQA GCE Mark Scheme 200 January series (a) (i) In experiments and 2, when [W] doubled rate doubles Stated or shown numerically (a) (ii) 2 Or shown as [x] 2 (b) (i) K = 6.20 x 0-5 (0.25) 2 x 0.50 =.98 x 0-3 Mol -2 dm 6 s - (b) (ii) Rate =.98 x 0-3 x x 0.0 Allow x 0-3 = 2.4(3) x 0-5 Allow conseq Ignore units 3

4 Chemistry - AQA GCE Mark Scheme 200 January series 2 (a) (i).60 = 0.05; (a) (ii) = (b) [NO] 2 [O 2 ]; [NO 2 ] 2 Allow 2*their mol O 2 Allow conseq Penalise [NO 2 /v] 2 etc Kc = x If no use of volume CE lose both marks = If eg forget square one o the terms when substituting AE lose but mark conseq Kc correct Mol dm -3 2 (c) Increased effect 4

5 Chemistry - AQA GCE Mark Scheme 200 January series 3 (a) Decrease CE if wrong 3 (b) Exothermic Higher pressure gives higher yield / moves to right Equilibrium moves to reduce pressure / favours side with fewer moles Increase in temperature decreases yield / moves to left Equilibrium moves to lower temperature / favours endothermic direction CE if wrong 5

6 Chemistry - AQA GCE Mark Scheme 200 January series 4 (a) K a = [H + ][A - ] [HA] 4 (b) K a = [H + ] 2 OR [H + ] = [A - ] [HA] Allow [HX] or similar [H + ] = (2.54 x 0-5 x 0.300) = 2.76 x 0-3 ph = (c) (i) ph almost unchanged/ (very) small increase/ stays the same OWTTE Penalise other than 2dp te 5.2 gets three ticks since only AE is to forget to take the square root Must be correct to score rest. NaOH reacts with H +, then H + replaced by more dissociation of HA Must make both points 6

7 Chemistry - AQA GCE Mark Scheme 200 January series 4 (c) (ii) [H + ] = =.5 x 0-5 [A - ] = K a [HA] [H + ] (OR = 2.54 x 0-5 x x 0-5 = (mol dm -3 ) ph = pk a log [HA] [A - ] pk a = = 4.60 log [A - ] [A - ] = 0.505) ( ) Allow answers between 0.50 and 0.5 te max 4 for this 7

8 Chemistry - AQA GCE Mark Scheme 200 January series 5 (a) 2 chloropropanoic acid 5 (b) Peak at δ.72 doublet CH 3 next to CH (one proton) Peak at δ4.44 Quartet CH next to CH 3 (three protons) 5 (c) Two triplets; Ignore reference to the COOH proton unless wrong 5 (d) 5 Allow Sn alternative mechanism Penalise Cl - removal of H in final mark 5 (e) (i) Allow + anywhere on _ NH 3 5 (e) (ii) Allow anywhere on _ COO Penalise covalent O _ Na 8

9 Chemistry - AQA GCE Mark Scheme 200 January series 5 (e) (iii) Allow anhydride 9

10 Chemistry - AQA GCE Mark Scheme 200 January series For each section: A totally wrong reagent scores zero. An incomplete reagent such as silver nitrate for Tollens, loses the reagent mark, but can get both observation marks. A wrong reagent such as [Ag(NH 3 ) 2 ] 2+ or bromide water loses the reagent mark and the next mark gained, i.e. can only score /3 if both observations correct. 6 (a) (i) Tollens [] reaction A Silver or mirror or grey or ppt B (not silver solution) [] Fehlings/ Benedict s reaction A [] [] Red ppt [] t red solution Brady s of 2,4- dnph [] reaction A [] (yellow/orange) xtals or ppt t yellow/orange solution [] sodium [] [] Bubbles or hydrogen A reaction B [] [] Penalise thing as an observation once in this question Carboxylic acid/h 2 SO 4 [] Schiff s [] (sweet) smell A reaction B [] [] reaction A Goes pink B [] [] Iodoform or I 2 /NaOH Yellow (ppt) A reaction B [] PCl 5 [] [] [] (misty) fumes A [] reaction B [] 0

11 Chemistry - AQA GCE Mark Scheme 200 January series If two tests given and results given correctly for both compounds in both tests then full marks should be awarded. If one test on A and a different test on B with only these results given If both results correct then score 2 marks. If either result wrong then score mark. If either test would not work as a distinction, then score 0. If the candidate omits the letters when referring to the pair of compounds. 6 (a) (ii) An identified (hydrogen) carbonate reaction C Bubbles or CO 2 D [] [] [] Correct metal reaction C Bubbles or H 2 D [] [] [] Ul or stated indicator change C Red or correct colour D [] PCl 5 [] [] [] reaction C Misty fumes D [] [] 6 max 6 (b) Compare with IR spectrum of known compound; (Exact) match (dependent on the first mark)

12 Chemistry - AQA GCE Mark Scheme 200 January series 7 (a) (a) (i) (ii) 2-methlybutan--ol Optical 7 (b) (i) Elimination t nucleophillic nor any other qualification. t just dehydration. 7 (b) (ii) Penalise CH 3 CH 2 each time Addition or radical; i.e. not additional 7 (b) (iii) Allow C 2 H 5 CH = CHCH 3. QoL 7 (b) (iv) t _ H 2 2

13 Chemistry - AQA GCE Mark Scheme 200 January series 8 CH 3 COCl + 2CH 3 CH 2 NH 2 CH 3 CONHCH 2 CH 3 + CHCH 2 (+) NH 3 Cl (-) () t molecular formula N-ethylethanamide () addition-elimination Equation must be completely correct to score 4 Wrong amine loses structure mark subtotal7 2 4 subtotal8 3

14 Chemistry - AQA GCE Mark Scheme 200 January series 8 EXTRA If CH 3 CH 2 Cl given for ethanoyl chloride Mark correct mechanisms and names similar to above BUT Max 2 marks 4

15 Chemistry - AQA GCE Mark Scheme 200 January series 9 (a) Conc HNO 3 Conc H 2 SO 4 HNO 3 + 2H 2 SO 4 NO H 3 O + + 2HSO 4 - (or HNO 3 + H 2 SO 4 NO H 2 O + HSO 4 - or HNO 3 + H + NO H 2 O ) If both conc missing can score one for both acids. If omitted can score one for reagents in the equation. Ignore temp/reflux etc. Or in two equations. Electrophilic substitution 5

16 Chemistry - AQA GCE Mark Scheme 200 January series 3 M arrow from within hexagon to N or to + on N. Don t penalise position of + on N or NO 2. Horseshoe must not extend beyond C2 to C6 but can be smaller + not too close to C. M3 arrow into hexagon unless Kekule. 6

17 Chemistry - AQA GCE Mark Scheme 200 January series 9 (b),4-dinitrobenzene Sn/Fe and HCl (conc or dil or neither) (or Sn/Fe and H 2 SO 4 (dil or neither) or H 2 /Ni ) Ignore extra NaH NOT HNO 3 at all NOT NaBH 4 / LiAlH 4 or Na/C 2 H 5 OH Allow C 6 H 4 (NO 2 ) 2 and C 6 H 4 (NH 2 ) 2 Allow 6H 2 if Ni/H 2 stated as reagents Lone pair or electron pair on N in S Delocalised into ring Less available(for protonation) that lp in T(dependent on first point) 9 (c) Allow NHCO- QoL Do not allow C 4 H 8. Ignore [ ] or n. But must have trailing bonds. 7