OCR_A level Chemistry_Marking Scheme 2_2020 | SPS F108 12.2_Carbonyl Compounds, Carboxylic Acids, Esters & Polyesters

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Carbonyl Compounds, Carboxylic Acids, Esters & Polyesters Mark Scheme 2 Level A Level Exam Board OCR Sub-Topic Time Allowed: 76 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 More]

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