Final. Mark Scheme. Chemistry CHEM4. (Specification 2420) Unit 4: Kinetics, Equilibria and Organic Chemistry

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1 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME Question : /A Question 2: /A Question 3: /A General ertificate of Education (A-level) June 203 hemistry EM4 (Specification 2420) Unit 4: Kinetics, Equilibria and rganic hemistry Final Mark Scheme

2 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME Question 4(a) Marking Guidance 3 Mark T penalise missing brackets. 3 R omments If wrong ester, no further mark Must be displayed formula + Allow radical with brackets as.. () Radical dot must be on Ignore errors in acylium ion. Ignore lone pair(s) on in addition to single electron 2

3 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME 4(b)(i) All3 or Fel3 3l + All3 4(b)(ii) 3 + If wrong no further marks. orrect equation scores 2 - contrast with 4(b)(iii) Allow + on or in equation. Ignore Friedel crafts. All4 Electrophilic substitution M + must be on of R here M arrow from within hexagon to or to + on 3 Gap in horseshoe must approximately be 3 3 R M centred around and not extend towards beyond 2 and 6 + not too close to arrow into hexagon unless Kekule allow arrow independent of structure, i.e. + on in intermediate loses not ignore base removing for 4(b)(iii) (3) R ot allow molecular formula for ethanoic anhydride or ethanoic acid. 3 (3)2) + orrect equation scores contrast with 4(b)(i) + 3 3

4 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME Question Marking Guidance 5(a)(i) 2-hydroxypropanoic acid R 2-hydroxypropan(--)oic acid 5(a)(ii) () Mark omments Do not penalise different or missing punctuation or extra spaces. Spelling must be exact and order of letters and numbers as here. an ignore -- before oic, but penalise any other numbers here. Allow 4363 R () (b)(i) Allow 2363 ucleophilic addition M4 for lp, arrow and + 3 M M lp and minus must be on M and M4 include lone pair and curly arrow. not allowed independent of M, but allow following some attempt at attack on carbonyl allow M for correct attack on + + rather than δ+ on = loses is for correct structure including minus sign but lone pair is part of M4 Allow arrow in M4 to of - with arrow forming cyanide ion. 5(b)(ii) Equal mixture of enantiomers / (optical) isomers 5(b)(iii) (Plane) polarized light If missing no further mark. (Polarised light) rotated by single enantiomer but unaffected by racemate Both needed; not allow bend, twist etc. 4

5 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME 5(c)(i) 3() + a 3()a + 2 R 3() + 3() + 2 5(c)(ii) [+] = Ka R p = pka p = (c)(iii) M buffer ot ambiguous mol formulae for product - must show a or 2a or or 2 Allow more than 2 decimal places but not fewer. Ignore acidic but penalise alkaline or basic. Any two out of the three marks, & M4 Large lactate concentration in buffer R sodium lactate completely ionised added acid reacts with/is removed by lactate ion or A or sodium lactate or salt R equation + + A A M4 ratio [A]/[A-] stays almost constant 5(d)(i) 3 3 orrect ester link allow All rest correct with trailing bonds 5(d)(ii) 3 (Poly)ester ie allow ester Ignore reaction of + with Ignore reference to equilibrium unless it is shown. Ignore + or p remains constant. B orrect answer scores 2 o marks if ester link missing R 3 Max 2 Ignore n here (compare with 5(d)(iv). Ignore brackets. If or on either or both ends, lose one, ie dimer scores If more than two repeating units, lose ot terylene. Ignore spaces and brackets in answer. 5

6 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME 5(d)(iii) 3 Allow any cyclic (d)(iv) 2 Penalise n here (compare with 5(d)(i) R 2 65 Ignore brackets. ot allow Ph for phenyl. 5(d)(v) In landfill, no air or UV, to assist decay R not enough water or moisture (to hydrolyse polyester) Allow landfill has/contains: no or few bacteria / micro-organisms / enzymes compared with compost heap R less oxygen R lower temperature. 6

7 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME Question Marking Guidance Mark omments 6(a) 3 + Allow 3+ and 3 3 6(b) 3 3 Allow protonated form, i.e. 3+ or (c) 2 Allow 2 2 6(d) Allow zwitterion with any Allow use of wrong

8 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME Question Marking Guidance Mark 7(a)(i) Dl3 or D2l2 or 6D6 or l4 7(a)(ii) 4 or four 7(a)(iii) Triplet or 3 or three 7(a)(iv),4-dichloro-2,2-dimethylbutane omments ot D2 Allow D3l Do not penalise different or missing punctuation or extra spaces. Spelling must be exact and order of letters and numbers as here. 7(b)(i) 3 or three 7(b)(ii) (cm-) Allow a single number within the range. R a smaller range entirely within this range. 7(b)(iii) hexane-2,5-dione Do not penalise different or missing punctuation or extra spaces. Spelling must be exact and order of letters and numbers as here. B so must have middle e 8

9 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME Question 8(a) Marking Guidance Mark (nucleophilic) addition-elimination 3 l 3222 M Allow attack by :2223 not allowed independent of M, but allow M for correct attack on + + rather than δ+ on = loses 223 If l lost with = breaking, max for M for correct structure with charges but lone pair on is part of M4 3 arrows in M4 can be shown in two separate steps. If drawn twice, mark first answer eg ignore missing + if missed off second structure nly allow M4 after correct / very close For M4, ignore R2 removing + but lose M4 for l removing + in mechanism, but ignore l shown as a product omments l 3 4 R2 M4 for 3 arrows and lp Allow wrong amine in M but penalise in Allow 37 in Minus sign on 3 loses M (but not M4 if 3 also shown here) -propylethanamide must be this name even if wrong amine used T -propylethaneamide 9

10 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME 8(b)(i) 3 3 Primary secondary ot allow ambiguous 372 BEWARE o mark for the original amine 3222 Allow Penalize wrong number of carbons but otherwise correct, first time only. tertiary 3 8(b)(ii) Label and structure must both be correct for each type to score the mark. Absorption at (cm-) in spectrum Allow trough, peak, spike. Ignore absorption at for bond in secondary - this is within fingerprint region. Allow any number in this range. If range missing, no further marks. If range linked to tertiary, no further marks. (bond) (only) present in secondary amine or not present in tertiary amine R This peak or absorption (only) present in spectrum of secondary amine or not present in spectrum of tertiary amine 0

11 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME 8(c)(i) M Route A : stage M4 Route A Intermediate Route A : stage 2 K Apply list principle for extra reagents or catalysts T T K/acid ot K/ Aqueous or ethanolic only scores after correct M ignore warm; acid here loses M & 32 or propanenitrile If intermediate wrong, max 2 for M & ie no mark for stage 2 ame alone must be exactly correct to gain M but mark on if name close But if intermediate close, eg nitrile or wrong nitrile, can award marks in stage 2 correct formula gains M (ignore name if close) If stage correct and intermediate is missing, can award marks in stage 2 contradiction of name and formula loses mark stage wrong & intermediate missing, no marks. 2 LiAl4 ether loses M4 but mark on i or Pt or Pd M5 3 With acid loses M6 & M7 Apply list principle for extra reagents or catalysts. M7 Excess 3 Ignore conc, ignore high P, ignore solvent. Route A disadv Toxic /poisonous K or cyanide or - or Allow 2 flammable/explosive etc. ot just dangerous. Ignore time reasons. Allow impure product. M6 8(c)(ii) Route B Apply list principle for extra reagents or catalysts. M5 only scores after correct M4 ot ab4 not Sn or Fe / l Allow (dil) acid after but not with LiAl4 Penalise conc acid. Expensive LiAl4 Ignore acidified R lower yield because 2 steps Route B disadv Further reaction/substitution likely

12 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME Question 9(a) Marking Guidance Mark omments M Lone pair on labelled b more available / more able to be donated than lone pair on labelled a Ignore (b) more readily accepts protons. Ignore (b) is stronger base. lp or electrons or electron density on labelled a: QoL QoL 9242 Any order. delocalized into (benzene) ring lp or electrons or electron density on labelled b: methyl/alkyl groups electron releasing or donating or (positive) inductive effect or push electrons or electron density 9(b) 2

13 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME Question Marking Guidance 0(a)(i) Mark Allow - or Mark two halves separately 2 6 omments lose each for missing trailing bonds at one or both ends or error in peptide link or either or both of or on ends ot allow (62) Ignore n 0(a)(ii) M in polyamides - bonding in polyalkenes - van der Waals forces Stronger forces (of attraction) in polyamides r bonding is stronger (must be a comparison of correct forces to score ) 9 Penalise forces between atoms or van der Waals bonds Do not award if refer to stronger bonds 3

14 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME 0(b)(i) (nucleophilic) addition elimination Minus sign on 2 loses M 4 not allowed independent of M, but allow M for correct attack on + + rather than + on = loses ( l 3 (3)-2 l 32 If l lost with = breaking, max for M 3 for correct structure with charges but lp on is part of M4 only allow M4 after correct/ very close For M4, ignore 3 removing + but lose M4 for l removing + in mechanism, M M4 for 3 arrows and lp ot allow 2 0(b)(ii) -methylpropanamide 0(c) 2S 2 0(d)(i) but ignore l as a product 3 ot -methylpropaneamide Allow - or amino-3-hydroxypropanoic acid 20 4

15 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME 0(d)(ii) 2 or allow 2 or 2 allow 2 2 Must be salts of aspartic acid 0(d)(iii) allow 2 Penalise use of aspartic acid once in d(iii) and d(iv) 2 3 0(d)(iv) allow 2 2 don t penalize position of + on 3 (l ) Penalise use of aspartic acid once in d(iii) and d(iv) allow +3 must show - bond don t penalize position of + on (3)3 ( 3)3 (Br ) 2 5

16 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME Question (a) Marking Guidance Benzene-,2-dicarboxylic acid (b) (c)(i) Mark l (c)(iii) Allow,2-benzenedicarboxylic acid Must show all bonds including trailing bonds Ignore n (c)(ii) omments 6 or six B Two ethanols but only one water 2 3 Ignore overlap with to the left or to the right, but must only include this one carbon. either or allow both (as they are identical)

17 ERRY ILL TUITI AQA EMISTRY A2 PAPER 30 MARK SEME (d) 2 3 LS 2 3 R (e)(i) Rate = k[dep] (e)(ii) Any two of [244]+ Allow + on or in [DEP] [093]+ + [25]. Dot must be on in radical RS Must have brackets but can be ( ) 2 Max experiment repeated/continued over a long period ot just repetition repeated by independent body/other scientists/avoiding bias investigate breakdown products Ignore animal testing results made public 23 7