abc Mark Scheme Chemistry 5421 General Certificate of Education 2005 examination - June series CHM4 Further Physical and Organic Chemistry

Transcription

1 Version.0 General Certificate of Education abc Chemistry 542 CM4 Further Physical and Organic Chemistry Mark Scheme 2005 examination - June series 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. Copyright 2005 AQA and its licensors. All rights reserved.

2 CM4 AQA GCE Mark Scheme, 2005 June series Question (a) propyl methanoate; COOC O - COO - + C 3 7 O COOC NaO COONa + C 3 7 O; order wrt A = ; order wrt NaO = ; Initial rate in Exp 4 = ; (b) (i) r(ate) = k[a] r(ate) = k[a][nao] 0 ; (penalise missing [ ] but mark on) (penalise missing [ ] once per paper) (if wrong order, allow only units mark conseq on their rate eqs) (penalise k a or k w etc) (d) (ii) k = ; 0.02 = 0.45; s - ; (iii) (large) excess of O - or [O - ] is large/high; [O - ] is (effectively) constant C [A] 2 O is the limiting factor ; (i) CO C 2 O ; propan(e)-,2,3-triol 2

3 AQA GCE Mark Scheme, 2005 June series CM4,2,3-propan(e)triol Glycerol; (ii) C 3 (C 2 ) 6 COONa or C 7 35 COONa or C 8 35 O 2 Na; (ignore 3 in front of formula but not if indicating trimer) (not just anion and penalise Na shown as covalently bonded) soap allow with detergent but not detergent alone; Total 5 Question 2 (a) (i) B; C; A; (ii) cresolphthalein thymolphthalein; (b) (i) -log[ + ]; (ii) [ + ] = (or.26 or.3) po = 4 - p; [O - ] = = 2.0; = 7.9(4) 0-3 ; (if [ + ] is wrong allow for [O - ] = K w /[ + ] or as numbers) (c) (i) K a = [ + ] 2 /[C 3 C 2 COO] [ + ] 2 /[A] [ + ] = [A - ] etc; [ + ] = or expression without numbers; = p = 2.90; 3

4 CM4 AQA GCE Mark Scheme, 2005 June series (ii) K a = [ + ] pk a = p; p = 4.87; (penalise dp once) Total 3 4

5 AQA GCE Mark Scheme, 2005 June series CM4 Question 3 (a) necleophilic addition; C 3 C 2 C O M2 C 2 5 or M4 C 3 C 2 C O NC + NC M M3 structure ; 4 (be lenient on position of charge on CN - ) (M2 not allowed independent of M, but allow M for correct attack on C+ if M2 show as independent first.) (+on C of C=O loses M2 but ignore + if correct) (M4 for arrow and lone pair (only allow for correct M3 or close)) (b) (i) 2-hydroxybutanoic acid 3 C (ii) C C COO 3 C C C COO (c) (i) geometric(al) or cis-trans C 3 O C C 2 C O (one unit only) (ignore brackets or n) (trailing bonds are needed) (ii) can be hydrolysed can be reacted with/attacked by acid/base/nucleophiles/ 2 O/O - ; (d) (i) 5

6 N CM4 AQA GCE Mark Scheme, June series C 3 C 2 C COO ; (allow N + 3 ) (ii) NC 3 C 3 C 2 C COO ; (or zwitterions product) (iii) nucleophilic substitution; Total 4 6

7 AQA GCE Mark Scheme, 2005 June series CM4 Question 4 (a) (i) 3 C C O or RCOC 3 ; (or description in words) (ignore trailing bonds) (ii) 3 C O or ROC 3 ; (allow if both (i) and (ii) give C 3 - or 3 C- only) (iii) C 2 C 2 or two adjacent methylene groups; (iv) C 3 C C 2 C 2 OC 3 O C 3 COC 2 C 2 OC 3 ; (b) (i) O in acids or (carboxylic) acid present (ii) C 3 C 3 C COO C 3 ; (c) reagent K 2 Cr 2 O 7 / + KMnO 4 / + Y no reaction no reaction Z orange to green or turns green purple to colourless or turns colourless Total 9 7

8 CM4 AQA GCE Mark Scheme, 2005 June series Question 5 (a) electrophilic substitution; conc NO 3; conc 2 SO 4 either or both conc missing scores one for both acids; (b) Sn or Fe/Cl (conc or dil or neither); (ignore extra NaO) Sn or Fe/ 2 SO 4 (dil or neither) (not NO 3 at all) or 2 /Ni (not NaB 4 / LiAl 4 or Na/C 2 5 O) C 3 C 3 + 6[] O NO 2 or 3 2 N 2 ; (c) 77 or 92; (d) C 3 N 3, (allow -N + 3 ) (e) G C 2 N 2 ; NC 3 ; Total 9 8

9 AQA GCE Mark Scheme, 2005 June series CM4 Question 6 (a) (must state correct effect on yield or rate to score the reason mark) T effect: higher temp: yield greater or shifts equm to right; effect: higher temp: rate increased; reason: endothermic more particles have E>E a more successful/productive collisions; P effect: higher pressure: yield less or shifts equm to left; effect: higher pressure: rate increased; reason: increase in gas moles L to R greater collision frequency; (b) M equilibrium moles of CO = = 36.6 M2 equilibrium moles of 2 = 46 2(26.2) = 93.6 M3 total no moles = = 56.4 M4 partial pressure = mole fraction x total pressure M5 K p = M6 = = p p CO C O 3 p ( ) ( ) ( ) 2 (.59) ( 2.22) ( 5.69) 2 2 M () 2.2()! ()!0-4 M8 MPa -2 kpa -2 Pa -2 (If no subtraction lose M, M2 and M3) (If 2 missed in M2, lose both M2 and M3) (If M gained but moles of 2 = 73.2 (i.e. double CO), M2 and M3 lost) (If M gained but mol 2 = 2( ), M2 and M3 lost) (If M and M2 correct but M3 lost for CE, penalise M6 also) (M4 can be gained from the numbers in the expression for M6 even if these numbers are wrong) (If Kp contains [ ] lose M5 but then mark on) (If chemically wrong expression for Kp, lose M5, M6 and M7 (allow M8 conseq on their K p )) (If divided by 9.5, or not used 9.5 at all, lose M6 and M7 (and M4)) (If tried to convert to kpa and is factor(s) of 0 out, penalise in M6 and allow M8 for kpa -2 ) Total 4 9

10 CM4 AQA GCE Mark Scheme, 2005 June series Question 7 (a) (nucleophilic) addition-elimination; M2 O allow C 2 5 O C 3 C 2 C Cl C 3 C 2 C Cl M 3 C N C 3 N 2 4 (M3 for structure) (M4 for 3 arrows and lone pair) (M2 not allowed independent of M, but allow M for correct attack on C+ if M2 show as independent first.) (+on C of C=O loses M2 but ignore + if correct) (Cl - removing + loses M4) O C 3 C 2 C NC3 ; (If M3 lost above for wrong C chain, do not penalise same error again here) (b) C 3 C 2 COCl + AlCl 3 [C 3 C 2 CO] + + AlCl 4 - ; (penalise wrong alkyl group once at first error) (position of + on electrophile can be on O or C or outside [ ]) (penalise wrong curly arrow in the equation or lone pair on AlCl 3 ) M M2 structure COC 2 C 3 COC 2 C 3 M3 arrow (horseshoe must not extend beyond C2 to C6 but can be smaller) (+ not too close to C) (penalise M2 if C 3 chain wrong again but allow M and M3) (M arrow from within hexagon to C or to + on C) (M3 arrow into hexagon unless Kekule) (allow M3 arrow independent of (don t penalise position of + on C of RCO+) ; 3 - AlCl M2 structure) AlCl 3 + Cl; (or can be gained in mechanism) 0

11 AQA GCE Mark Scheme, 2005 June series CM4 (c) M C 3 C 2 COCl + 2 O C 3 C 2 COO + Cl (penalise wrong alkyl group once at first error) M2 M r of C 3 C 2 COCl = 92.5 (if M r wrong, penalise M2 only) M3 moles of C 3 C 2 COCl =.48/92.5 = 0.06 M4 moles NaO = = (allow for 2 conseq to wrong no of moles) M5 volume of NaO = 0.032/0.42 = dm 3 or 76.2 cm 3 (with correct units) (if 2 missed in M4 lose M5 also) Total 6

12 CM4 AQA GCE Mark Scheme, 2005 June series GENERAL GANIC POINTS F MARKING CM4 Curly arrows These must show the movement of a pair of electrons, i.e. from a bond or a lone pair either to an atom (example ) or to the space between two atoms (example 2) Example - correct Example 2 - correct R R 3 N C Br 3 N C Br Curly arrows never start at an atom e.g. the right hand arrow in example 3 is wrong Example 3 wrong R 3 N: C Br 2 Incorrect Structures which are generally penalised once per paper: a) Sticks, i.e. bonds without (hydrogen) atoms on their ends, e.g. C b) Incorrectly bonded functional groups e.g. correct R C O O C R R C 2 N C R wrong O R C O O C R R C N 2 C R O Alkyl groups, however, can be written in several different ways. The following alkyl group arrangements are allowed as correct: 2

13 AQA GCE Mark Scheme, 2005 June series CM4 C 3 3 C C 3 C 3 C 3 c) cyclohexane for benzene penalised once per paper 3