GE AS and A Level hemistry AS exams 2009 onwards A2 exams 2010 onwards Unit 4: Specimen mark scheme Version 1.1
Version 1.1: 07/07 abc General ertificate of Education hemistry 2420 EM4 Kinetics, Equilibria and rganic hemistry Mark Scheme Specimen Paper
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GE EMISTRY UNIT 4 SPEIMEN MARK SEME / VERSIN 1.1 Question 1 (a) (i) 2 (ii) 0 (b) (i) rate/[n 2 ] 2 [ 2 ] 13 mol dm 3 (ii) 1.9 10 3 (iii) Step 2 Question 2 (a) (i) + 3D 2A + B (ii) mol dm 3 (iii) (forward reaction is) exothermic or more products formed (b) (i) Moles of iodine = 0.023 Moles of I = 0.172 (ii) [ K c = 2 ][ I2 ] 2 [ I] (iii) V cancels in K c expression (iv) 2 ( 0. 023) K c = 2 ( 0. 172) = 0.0179 or 1.79 10 2 (v) K c = 55.9 or 56 onseq i.e. (answer to (iv)) 1 Question 3 (a) (i) B A (ii) cresolphthalein or thymolphthalein (b) p = log[ + ] + 2 [ ] K a = or [ + ] = [A ] [3] [ + ] = 1.74 10 5 0.15 (or 1.62 10 3 ) p = 2.79 (penalise 1 dp or more than 2dp once in the qu) Question 4 3
GE EMISTRY UNIT 4 SPEIMEN MARK SEME / VERSIN 1.1 (a) (i) addition of small amounts of acid send eqm to left or extra + removed by reaction with 3 ratio [ 2 3 ]/[ 3 ] remains constant hence [ + ] and p remain const (ii) p = 7.41 [ + ] = 3.89 10 8 mol dm 3 [ + ][3 ] K a = [23] 8 2 (3.89 10 )(2.5 10 ) = = 7.78 10 8 mol dm 3 2 1. 25 10 allow error carried forward mark. Do not penalise twice. (b) (ii) moles + added = 10 10 3 1.0 = 0.01 moles ethanoic acid after addition = 0.15 + 0.01 = 0.16 moles ethanoate ions after addition = 0.10 0.01 = 0.09 [ + ] = K a [ [ = 1.74 10 5 3 3 ] ] 0.16 / V 0.09 / V p = 4.51 Question 5 (a) (i) ( 3 ) 2 2 N (ii) 2 N ( 3 ) 2 N ( 3 ) 2 (iii) hydrogen bonding (do not allow bonding) QW do not penalise any error twice. (b) (i) 3 3 3 4
GE EMISTRY UNIT 4 SPEIMEN MARK SEME / VERSIN 1.1 (ii) 3 2 3 (iii) Isomer must be saturated or must not contain a double bond (c) ( 2 ) 2 N ( 2 ) 6 N (2) (d) (i) heat/reflux with aqu Na poly(alkene) is inert/ no reaction polyamide is hydrolysed (or undergoes hydrolysis) to form acid salt and alcohol (ii) e.g combustion heat energy produced toxic gases produced QW Question 6 (a) GL or distillation (b) = (c) (i) l has two isotopes (ii) 3 4 7 l +. 3 + 2 4 l. (d) (i) e.g. Dl 3 or l 4 (ii) Si( 3 ) 4 (e) 0 and 3 (f) 3 3 l (g) 3 2 2 l or ( 3 ) 2 l 5
GE EMISTRY UNIT 4 SPEIMEN MARK SEME / VERSIN 1.1 Question 7 (a) (i) There are three pairs of equivalent carbon atoms (ii) 75ppm (b) (i) 4 (ii) 2 (c) Each structure can represent a pair of cis/z and trans/e isomers R ptical isomers Question 8 Mark Range The marking scheme for this part of the question includes an overall assessment for the Quality of Written ommunication (QW). There are no discrete marks for the assessment of QW but the candidates QW in this answer will be one of the criteria used to assign a level and award the marks for this part of the question Descriptor an answer will be expected to meet most of the criteria in the level descriptor 45 23 01 claims supported by an appropriate range of evidence good use of information or ideas about chemistry, going beyond those given in the question argument well structured with minimal repetition or irrelevant points accurate and clear expression of ideas with only minor errors of grammar, punctuation and spelling claims partially supported by evidence good use of information or ideas about chemistry given in the question but limited beyond this the argument shows some attempt at structure the ideas are expressed with reasonable clarity but with a few errors of grammar, punctuation and spelling valid points but not clearly linked to an argument structure limited use of information or ideas about chemistry unstructured errors in spelling, punctuation and grammar or lack of fluency (a) (i) M r of 6 5 N 2 = 93 M r of 3 l = 78.5 total M r of reagents = 264.5 % atom economy = Mrof wanted product total Mr of all reagents 100 QW 6
GE EMISTRY UNIT 4 SPEIMEN MARK SEME / VERSIN 0.2 = 135 264. 5 100 = 51.0 % (ii) 10 expected yield = 0.5 135 = 7.26 kg 93 5. 38 % yield = 100 = 74.1 % 7. 26 (iii) Although yield appears satisfactory (74%) % atom economy is only 51% nearly half of the material produced is waste and must be disposed of QW QW (b) (nucleophilic) additionelimination M2 3 l M1 6 5 N 2 3 6 5 N l M3 for structure M4 for 3 arrows and lone pair 3 N 6 5 QW (2) (4) (c) N 3 + 2 2 S 4 N 2 + + 3 + + 2S 4 M1 N 2 M2 structure M3 arrow (3) N 2 Question 9 3 N or ethanenitrile S 3 2 N 2 or ethylamine Step 1 KN aq/alcoholic Step 2 2 Ni W secondary amine 3 3 2 N 3 (Br ) 3 7
GE EMISTRY UNIT 4 SPEIMEN MARK SEME / VERSIN 1.1 nucleophilic substitution Question 10 Acidified potassium dichromate(vi) Turns green with propan2ol and propanal No reaction with hexene and 1bromopropane Tollens with propan2ol and propanal only propanal gives silver mirror Bromine water Decolourised by hexene No reaction with 1bromopropane Warm Na followed by acidified AgN 3 White ppt with 1bromopropane 8