Carbonyl Compounds,
Carboxylic Acids, Esters & Polyesters
Mark Scheme 2
Level A Level
Exam Board OCR
Sub-Topic
Time Allowed: 76
... [Show More] minutes
Score: /63
Percentage: /100
Grade Boundaries:
A* A B C D E U
>85% 77.5% 70% 62.5% 57.5% 45% <45%
Question Answer Mark Guidance
1 (a) monomers join/bond/add/react/form polymer/form chain
AND another product/small molecule e.g. H2O/HCl
QWC must spell AND use ‘monomer(s)’ correctly throughout
1 IGNORE ‘two’ when referring to monomers, ie (two) monomers ……...
(b) (i)
ester link
Note: Any ester link shown must be correct rest of the structure
2 ALLOW correct structural OR displayed OR skeletal formula
OR mixture of the above (as long as unambiguous)
ALLOW benzene ring for C6H5
‘End bonds’ MUST be shown (do not have to be dotted)
ALLOW one or more repeat units but has to have a whole number of repeat units (ie does not have to be two)
For ester, DO NOT ALLOW
ALLOW structure with no O at left end and COO at right end
IGNORE brackets
IGNORE n
(ii)
1 ALLOW correct structural OR displayed OR skeletal formula
OR mixture of the above (as long as unambiguous)
ALLOW one or more repeat units but has to have a whole number of repeat units (ie does not have to be two)
‘End bonds’ MUST be shown (do not have to be dotted)
IGNORE brackets
IGNORE n
Question Answer Mark Guidance
(c) compound C
compound D and compound E
3 ALLOW correct structural OR displayed OR skeletal formula
OR mixture of the above (as long as unambiguous)
ALLOW CH2C(CH3)COOH
ALLOW D and E by ECF from an incorrect structure of C provided that C contains a double bond and molecular formulae of D and E is C4H8O3 with H2O added across double bond
(d) (i)
1 ALLOW correct structural OR displayed OR skeletal formula
OR mixture of the above (as long as unambiguous)
e.g. (CH3)2CHOH
DO NOT ALLOW –HO
IGNORE working (ie other structures) provided correct structure of propan-2-ol is shown
IGNORE name (even if wrong)
Quest on er Mark Guidance
(d) (ii)
1 ALLOW correct structural OR displayed OR skeletal formula
OR mixture of the above (as long as unambiguous)
OR (2-)methylpropanoic acid
DO NOT ALLOW incorrect name (will CON a correct structure)
ALLOW acyl chloride: (CH3)2CHCOCl
IGNORE working provided correct structure of propan-2-ol is shown
O
OR acid anhydride:
O
O O
(iii) ANNOTATIONS MUST BE USED
Hydrogen bonds form with water
Note: Can be shown in diagram as dashed line,
ie (no label required)
DO NOT CON ‘hydrogen bond’ from an incorrect hydrogen bond in diagram ALLOW a diagram showing hydrogen bonds with water, dipole and lone pair are not required
ALLOW a hydrogen bond to C=O, ie C=O---H–O
IGNORE bond angles
Diagram does not need to show all of mandelic acid (IGNORE if wrong)
Mandelic acid forms more hydrogen bonds (with water)
ORA ALLOW any comparison of numbers of hydrogen bonds provided that mandelic acid has more hydrogen bonds
Mandelic acid has an extra OH
OR 2 OH groups
OR has a COOH group
ORA
3 DO NOT ALLOW ‘No –OH groups in ester (as there are)’
DO NOT ALLOW reference to –OH– / hydroxide
IGNORE reference to carbon chain and van der Waals’ forces
Note: If a response compares Ester 1 with Ester 2 rather than with mandelic acid, maximum of 2 marks:
1st mark hydrogen bonds
2nd mark Ester 2 has more Os/oxygens
OR Ester 2 forms more hydrogen bonds
Question Answer Mark Guidance
(d) (iv) To test for (adverse) side effects
OR to test toxicity
OR to test for irritation
1 ALLOW a stated adverse side effect,
eg allergy, carcinogenic, etc
IGNORE references to optical isomers, chirality, etc
IGNORE vague statements such as harmful to skin, dangerous to skin, corrosive to skin, reacts with skin
ALLOW company liable to litigation/damages
Total 13
2
Equations
CH3COCHO + 4[H] CH3CHOHCH2OH
CH3COCHO + [O] CH3COCOOH
Reduction reagents and observation
Methylglyoxal is reduced by NaBH4
Oxidation reagents and observation
Methylglyoxal is oxidised by H2SO4 AND K2Cr2O7
Observation: turns green OR blue
OR
Methylglyoxal is oxidised by Tollens’ reagent
Observation: Silver (mirror)
1
1
1
2 ANNOTATIONS MUST BE USED
Throughout question, ALLOW correct structural OR displayed
OR skeletal formula
DO NOT ALLOW molecular formulae
ALLOW partial reduction (ie reduction of either C=O group)
[H] implies reduct
[O] implies oxidat
reduced AND reagent are both required for the mark ALLOW link to equation with [H] for reduction ALLOW LiAlH4 as alternative for NaBH4
ALLOW any recognisable attempt at name
IGNORE any reference to acids
oxidised AND reagent are both required for the mark ALLOW link to equation with [O] for oxidation ALLOW Na2Cr2O7 instead of K2Cr2O7
ALLOW H+ AND Cr2O 2– OR H+ AND CrO 2–
7 4
If name given, ALLOW dichromate OR dichromate(VI)
ALLOW acidified dichromate
ALLOW any strong acid
If formulae used, formulae must be correct
ALLOW AgNO3 in ammonia OR ammoniacal AgNO3
ALLOW oxidised by manganate Observation: decolourised
Note: If one reaction is identified as oxidation, assume the other is reduction (and vice versa) [Show Less]