OCR_A level_Chemistry_Marking Scheme 3_2020 | SPS F108 12.3_Carbonyl Compounds, Carboxylic Acids, Esters & Polyesters

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SPS F108 12.3_Carbonyl Compounds, Carboxylic Acids, Esters & Polyesters_A level_OCR_Chemistry_Marking Scheme 3 Carbonyl Compounds, Carboxylic Acids, 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 More]

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