SPS F108 12.3_Carbonyl Compounds, Carboxylic Acids, Esters & Polyesters_A level_OCR_Chemistry_Marking Scheme 3
Carbonyl Compounds,
Carboxylic Acids,
... [Show More] Esters & Polyesters
Mark Scheme 3
Level A Level
Exam Board OCR
Sub-Topic
Time Allowed: 78 minutes
Score: /65
Percentage: /100
Grade Boundaries:
A* A B C D E U
>85% 77.5% 70% 62.5% 57.5% 45% <45%
Question er Mark Guidance
1 (a) (CH3CO)2O + CH3CH(OH)CH3
CH3COOCH(CH3)2 + CH3COOH ALLOW correct structural OR displayed OR skeletal formula ALLOW combination of formulae as long as unambiguous DO NOT ALLOW molecular formulae
1st mark
Correct structure of ester: CH3COOCH(CH3)2
ALLOW (CH3)2CHOOCCH3 OR (CH3)2CHOCOCH3
2nd mark
Equation contains correct formulae for (CH3CO)2O, CH3CH(OH)CH3 AND CH3COOH
2
(b) (i) (relative) solubility 1 IGNORE partition
DO NOT ALLOW adsorption OR absorption
(ii) The esters would have similar retention times
AND
similar structures/molecules OR same functional groups
OR similar polarities OR similar solubilities
Alcohol would have short retention time
AND
alkane would have long retention time
2
IGNORE similar properties
Question er Mark Guidance
(c) Elemental analysis and molecular formula – 2 marks
Use of percentages (to find EF) AND 144
Molecular formula = C8H16O2
2
marks ANNOTATIONS MUST BE USED
Working
C : H : O = 66.63/12 : 11.18/1
5.5525 : 11.18
4 : 8
Alternative method:
:
:
:
22.19/16
1.386875
1
carbon: (144 x 66.63/100)/12 = 8
hydrogen: (144 x 11.18/100)/1 = 16
oxygen: (144 x 22.19/100)/16 = 2
ester structure – 4 marks
CH3 O
H3C C CH2 C
CH3
O
CH2
CH3
ALLOW correct structural OR displayed OR skeletal formula ALLOW combination of formulae as long as unambiguous NO ECF from earlier structures
If not fully correct award following marks:
4
marks If structure an ester of formula C8H16O2
OR the organic structure contains C(CH3)3
If structure is an ester of formula C8H16O2
AND ester contains C(CH3)3
If structure is an ester of formula C8H16O2
AND ester contains O–CH2C(CH3)3
AND ester contains CH3CH2COO
i.e. If the ester link is reversed
O CH3
CH3 CH2 C O CH2 C CH3
CH3
IGNORE any name
Question er Mark Guidance
NMR analysis – 4 marks NOTE: Each peak can be identified from:
• its value: ± 0.2 ppm
• a range, eg ‘the peak between 2 and 3’
• its relative peak area
(CARE two peaks have an area of 2)
• its splitting
(CARE: two peaks are singlets)
• labelling on the spectrum
------------------------------------------------------------
Triplet (at δ 1.3) shows an adjacent CH2
OR triplet (at δ 1.3) shows (C with) 2 adjacent Hs/protons
(because of splitting: so triplet) QWC: triplet must be spelled correctly
ALLOW neighbouring Hs for adjacent to Hs
Peak at (δ) 2.2 shows H adjacent to C=O
AND
adjacent to (C with) no hydrogens
(because of no splitting: so singlet)
For peak at (δ) 2.2
ALLOW singlet at (δ) 2.2
ALLOW singlet labelled 2
Peak at (δ) 4.2 shows H–C–O
AND
adjacent CH3 OR 3 adjacent Hs/protons
(because of splitting: so quartet)
For peak at (δ) 4.2
ALLOW quartet (labelled 2)
Peak at (δ) 0.9 show 3 x CH3
(because of singlet and area 9) 4
marks ---------------------------------------------------------
Check back for any responses added to spectra
ADD ^ MARK TO THE SPECTRUM PAGE TO SHOW THAT IT HAS BEEN LOOKED AT
Total for 4(c) 10
Total 15
Question Answer Mark Guidance
2 (a) propane-1,2,3-triol 1 ALLOW absence of ‘e’ after ‘propan’
ALLOW 1,2,3-propanetriol
ALLOW absence of hyphens
1, 2 and 3 must be clearly separated:
ALLOW full stops: 1.2.3 OR spaces: 1 2 3
DO NOT ALLOW 123
2 (b) (i)
methanol OR ethanol
AND
renewable
1 BOTH points required for the mark
ALLOW correct structural OR displayed OR skeletal formula
DO NOT ALLOW molecular formulae
ALLOW easy/cheap to manufacture/produce as alternative for renewable/from plants/from fermentation/burns more easily/efficiently
(b) (ii) equilibrium shifts to right 1 ALLOW equilibrium shifts in forward direction
ALLOW more products form
ALLOW greater yield OR fully reacts OR goes to completion
DO NOT ALLOW improves atom economy
--
-
-
-
- [Show Less]