PMT GCE. Chemistry A. Advanced GCE F324. Mark Scheme for June Oxford Cambridge and RSA Examinations

Transcription

1 GE hemistry A Advanced GE F324 Mark Scheme for June 200 xford ambridge and RSA Examinations

2 R (xford ambridge and RSA) is a leading UK awarding body, providing a wide range of qualifications to meet the needs of pupils of all ages and abilities. R qualifications include AS/A Levels, Diplomas, GSEs, R Nationals, Functional Skills, Key Skills, Entry Level qualifications, NVQs and vocational qualifications in areas such as IT, business, languages, teaching/training, administration and secretarial skills. It is also responsible for developing new specifications to meet national requirements and the needs of students and teachers. R is a not-for-profit organisation; any surplus made is invested back into the establishment to help towards the development of qualifications and support which keep pace with the changing needs of today s society. This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which marks were awarded by Examiners. It does not indicate the details of the discussions which took place at an Examiners meeting before marking commenced. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes should be read in conjunction with the published question papers and the Report on the Examination. R will not enter into any discussion or correspondence in connection with this mark scheme. R 200 Any enquiries about publications should be addressed to: R Publications P Box 5050 Annesley NTTINGAM NG5 0DL Telephone: Facsimile: publications@ocr.org.uk

3 Allow Kekulé structures throughout a Bond length intermediate between/different from (short) = and (long) hydrogenation less exothermic than expected (when compared to hydrogenation for cyclohexene) nly reacts with Br 2 at high temp or in presence of a halogen carrier / resistant to electrophilic attack Please annotate, use ticks to show where marks are awarded b i compound A N 2 if N 2 in wrong position penalise here and EF for rest of b(i) and b() 3 ALLW all carbon carbon bonds the same length ALLW hydrogenation less (negative) than expected ALLW hydrogenation different from that expected D NT ALLW halogenation/hydration ALLW doesn t decolourise/react with/polarise Br 2 ALLW doesn t undergo addition reactions (with Br 2 ) ALLW any 4-nitro-,3-dimethylbenzene drawn in any orientation ALLW N drawn in any orientation compound B N 2 4 ALLW any 4-amino-,3-dimethylbenzene drawn in any orientation EF amine of incorrect compound A (e.g. position of N 2 or lack of methyl sticks/groups) compound N N ALLW diazonium chloride salt of,3-dimethylbenzene EF diazonium salt/compound of incorrect compound B IGNRE l ion allow N N not allow N 2

4 ALLW if charge is floating between the two Ns only if it is closer to the correct N allow not allow N N N N compound D ALLW any of - ALLW in place of 2

5 Equation to show formation of N 2 ion mark N S 4 3 2S 4 N 2 ALLW N 3 2 S 4 2 S 4 N 2 N 3 2 S 4 S 4 2 N 3 2 N 2 If N 2 is in correct position do not penalise even if compound A in b(i) is not in correct position N 2 mark 4 curly arrow from bond back to reform ring AND correct products N 2 N 2 5 ALLW mark 2 curly arrow must be from,3- dimethylbenzene to N 2 and EF for marks 3 and 4 D NT ALLW intermediate -ring must be more than / 2 way up N 2 mark 2 curly arrow from ring to N 2 mark 5 - S 4 mark 3 intermediate with ring broken in the correct place 2 S 4 Link to compound A in part (i) cannot score full marks [in b(i) & b()] if N 2 is not adjacent to a methyl ALLW 3 s shown ALLW 3 S S 4 i 2 No other correct response Total 3 3

6 2 a i ALLW for both marks Ester group must be displayed to get both marks and must contain 4 s ALLW for one mark ALLW for one mark 2 2 ALLW Kekulé structure / ( 2 ) 2 ALLW one mark if end bonds missing ALLW mark if the 2 2 is drawn skeletally ALLW for ALLW mark if repeat unit shows a displayed ester group and contains a benzene ring and two other carbons D NT ALLW ALLW Kekulé structure/ ( 2 ) 2 2 for ester groups 6 4 if already penalised in a(i) 4

7 b i ALLW any order of elements ALLW or = ALLW / 2 ALLW Penalise incorrect bond linkage in 2b() only. Do not penalise elsewhere on the paper ALLW ( 2 ) 2 c i - (Na ) 2 ALLW any of the following for mark Na - or D NT ALLW any other response - Na or 2 - Na (PGA is) (bio)degradable R photodegradable R hydrolysed (but hydrocarbon based polymers are nonbiodegradable) ne of (bio)degradable R photodegradable R hydrolysed must be spelt correctly if one spelt correctly and another incorrectly spelt ALLW mark ALLW broken down by bacteria (must be spelt correctly) ALLW degrade as alternative to degradable ALLW undergoes hydrolysis as alternative to hydrolysed IGNRE any additional information if the additional information is correct e.g. biodegradable and doesn t produce toxic gases D NT ALLW any additional information if the additional information is incorrect e.g. biodegradable and can be recycled Total 9 5

8 3 a Alternative approaches Tollens test AND silver precipitate/mirror is the aldehyde react with 2,4-DNP() and orange precipitate must be the ketone 2,4-DNP() AND orange precipitate is either aldehyde R ketone ALLW carbonyl R = Tollens test & silver ppt/mirror is the aldehyde Tollens test AND silver precipitate/mirror is the aldehyde react with carbonate/ hydrogencarbonate/ Na/Mg and fizzes/ bubbles/ effervesces/ gas evolved must be the (carboxylic) acid 2,4-DNP() and no orange precipitate is the (carboxylic) acid Tollens test & silver ppt/mirror is the aldehyde 4 ALLW ammoniacal AgN 3 / Ag (N 3 ) 2 / Ag (N 3 ) ALLW acidified dichromate R Fehlings as an alternative to Tollens observation turn green R red precipitate respectively ALLW acidified manganagate(vii) and observation as either brown precipitate/decolourised/pale pink ALLW Brady s (reagent) ALLW orange/red/yellow for colour of the 2,4-DNP() precipitate ALLW solid/crystals in place of precipitate IGNRE any reference to melting points ALLW Pl 5 as a test for the acid observation would be white fumes (of l) ALLW detection of (carboxylic) acid by reacting with an alcohol to make an ester but no mark for the observation. D NT ALLW detection of (carboxylic) acid by p or indicator Please annotate, use ticks to show where marks are awarded b Peak in range (cm ) or (around) 3000 shows [need wavenumber (or range) and bond] D NT ALLW single peak quoted within range other than 3000 (cm ) for D NT ALLWrange (cm ) IGNRE any reference to - or = 6

9 c Alternative approaches depending on whether or not the aldehyde is correct ALLW 3-methylbutanal, any correct unambiguous structure ALLW two marks for correct aldehyde with no explanation Doublet indicates adjacent is bonded to only R (relative) peak area indicates 2 x 3 (in the same environment) Doublet indicates adjacent is bonded to only AND (relative) peak area indicates 2 x 3 (in the same environment) ALLW doublet/peak at 0.9ppm due to R ALLW the splitting shows adjacent to /environment that contains /proton ALLW 6 s/ protons in same environment D NT ALLW 6 s in same environment next to d i If aldehyde is correct ( 3 ) 2 2 If aldehyde is correct only need to explain doublet R peak areas If aldehyde identified is incorrect if aldehyde is incorrect must explain both doublet or peak areas e.g. 3 3 ALLW displayed/skeletal formulae would score two marks if the doublet and the peak areas were correctly explained ketone 3 There are 4 (different ) environments ALLW 2 s are in same environment/equivalent (therefore) it is ketone 2 / ALLW 3-methylbutan(-2-)one/ any correct unambiguous structure ALLW 2-methylbutan-3-one 3 ( responsible for peak at = 20 ppm) is =/carbonyl carbon Total 2 ALLW 7

10 4 a i The time (from the injection of the sample) for the component to leave the column ALLW time from injection to detection ALLW time spent in column ALLW time taken to reach detector They have similar retention times ALLW both are esters therefore partition/adsorption/retention times will be very similar ALLW EF if they describe R f values in part a(i) ALLW same retention times b i i Butylbutanoate ALLW butyl butanoate ALLW but--yl butanoate hydrocarbon chain must be correct for one mark ester group and ethyl group must be correct for one mark 2 D NT ALLW butanyl butanoate ALLW any correct unambiguous structure/ 3 ( 2 ) / 3 ( 2 ) ( 2 ) 4 () D NT ALLW etc ALLW 2 for ester l ALLW mark for correct 2,4-decadiene structure e.g. ALLW mark for correct ethyl oate structure e.g. or or 2 5 8

11 2 R R 2 R ALLW 2 2 any orientation of the three fatty acids c. react phenylethanal with 2 S 4 /K 2 r 2 7 if either phenylethanoic acid or 2- phenyethanol not prepared automatically lose two marks 2. to get phenylethanoic acid/ mark 2 can be scored if dichromate is used without being acidified 3. react phenylethanal with NaB 4 4. to get 2-phenylethanol/ mark 3 must be correct to score mark 4 5. react phenylethanoic acid with 2-phenylethanol. If both already correctly named ALLW acid and alcohol 6. 2 S 4 if linked to the reaction of an alcohol and acid 7. reflux in either () or (5) or catalyst used in (5) QW must spell catalyst or reflux correctly 7 ALLW & r or 2 S 4 /Na 2 r any other oxidising agent or other named acid please consult with TL ALLW LiAl 4 as alternative to NaB 4 phenylethanoic acid & phenylethanol must be unambiguously identified by either name or formula D NT ALLW or oxidised to form(a carboxylic) acid or reduced to form alcohol for marks 2 and 4 ALLW conc 2 S 4 D NT ALLW dilute or 2 S 4 (aq) D NT ALLW just acid catalyst D NT ALLW l, N 3 Please annotate, use ticks to show where marks are awarded Total 3 9

12 5 a i ALLW * in place of circle ALLW if circle extends to include N Mark production of a single isomer is more expensive/difficult R separation of the single isomer is expensive/difficult 4 Mark 2 one of the isomers is more (pharmacologically) active or one of the isomers might have adverse/harmful/nasty side effects IGNRE any reference to dosage ALLW one is more effective/works (better) Marks 3 and 4 problems are overcome by using: Enzymes/bacteria/biological catalyst hiral synthesis hiral catalyst or transition metal complex Start with a natural chiral molecule or chiral pool any D NT ALLW use naturally occurring isomer unless stated that it is a chiral compound D NT ALLW transition metal ion D NT ALLW pool synthesis hiral pool synthesis scores (not 2) marks b i 2 2 N N 2 ALLW N 2 ALLW epoxy ethane as 2 4, ( 2 ) 2, 2 2 ALLW product as ( 2 ) 2 N 2 D NT ALLW product as 2 7 N 2 2 N 2 2 ALLW ( 2 ) 2 ALLW displayed/skeletal formula D NT ALLW molecular formula 0

13 c i 2 2 N 3 l - Must show l ion ALLW 2 2 N 3 l if formula is correct and both charges not shown ALLW ( 2 ) 2 / any correct unambiguous structure D NT ALLW ions joined by covalent bonds 2 2 N 3 S - Must show S ion ALLW if formula is correct and both charges not shown ALLW ( 2 ) 2 / any correct unambiguous structure ALLW 2 2 N 3 S 2-2 d i Both N 2 and are joined to the same ALLW 2 N 2 or R(N 2 ) 2 R The 4 groups/atoms attached to the can be in any order but must be adjacent. ( ) not essential 2 2 N 2 2[] 2 N 2 2 ALLW ( 2 ) 2 D NT ALLW molecular formula e i Question 5e is followed by two blank lined pages (5 and 6) which candidates can use instead of requesting additional paper. Please check to see whether or not pages 5 or 6 have been used

14 e i Isomer F N 2 2 ALLW ( 2 ) 4 N 2 / ALLW any correct unambiguous structure of -aminobutan-4-ol Isomer G * * ALLW 3 ()(N 2 ) 3 ALLW any correct unambiguous structure of 2-aminobutan-3-ol. N 2 * not required Total 3 2

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