OCR A Jan 2011 Paper 4 Q2 (with explained solutions) |

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OCR A Jan 2011 Paper 4 Q2

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2 Esters of fatty acids are used as biodiesels. These esters can be produced from triglycerides by the transesterification process below. R' R' R' 3 ROH NaOH catalyst heat R' O R HO HO OH triglyceride biodiesel glycerol (a) Give the systematic name of glycerol.[1] (b) (i) Suggest a suitable alcohol, ROH, that could be used industrially to make biodiesel. Justify your answer.[1] (ii) The alcohol, ROH, is added in excess. Suggest why the alcohol has to be in excess.[1]OCR 2011<br />
(c) Esters can also be made by reacting an alcohol with either a carboxylic acid or with an acid anhydride. Write equations for the formation of ethyl propanoate, CH3CH2COOCH2CH3, starting from: a carboxylic acid and an alcohol, an acid anhydride and an alcohol. (d) Compound A, C4H8O3, can lose water to form either: compound B, a cyclic ester OR compound C, a polyester. Identify compounds A, B and C. [2] compound A compound B compound C [3] [Total: 8] Turn overOCR 2011<br />

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F324 Question Answer 2 (a) propane-1,2,3-triol (cid:57) Mark Scheme January 2011 Mark Guidance 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 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 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 (b) (i) methanol OR ethanol AND renewable (cid:57) (b) (ii) equilibrium shifts to right (cid:57)<br />
F324 Question Answer 2 (c) CH3CH2COOH + CH3CH2OH (cid:111) CH3CH2COOCH2CH3 + Mark Guidance Mark Scheme January 2011 H2O (cid:57) (CH3CH2CO)2O + CH3CH2OH (cid:111) CH3CH2COOH (cid:57) CH3CH2COOCH2CH3 + ALLOW correct structural OR displayed OR skeletal formula ALLOW combination of formulae as long as unambiguous DO NOT ALLOW molecular formulae ALLOW further esterification, ie (CH3CH2CO)2O + 2CH3CH2OH (cid:111) 2CH3CH2COOCH2CH3 + H2O ALLOW linear formula for anhydride, ie CH3CH2COOCOCH2CH3 If incorrect carboxylic acid/anhydride/alcohol is used, ALLOW ECF for second equation<br />
Mark Scheme January 2011 Mark Guidance F324 Question Answer 2 (d) HO CH2 CH2 CH2 COOH OR CH3 HO CH CH2 COOH OR C2H5 HO CH COOH OR CH3 HO CH2 CH COOH OR CH3 HO COOH CH3 H2C H2C C H2 OR H2C HC OR CH C H3C C2H5 H3C O OR CH H2C OR H3C H3C CH2 CH2 CH2 C OR CH3 CH CH2 C OR C2H5 CH OR CH3 CH2 CH OR CH3 CH3 Mark A, B and C independently ie (cid:120) A can be any of the alternatives in the 1st column (cid:120) B can be any of the alternatives in the 2nd column (cid:120) C can be any of the alternatives in the 3rd column ALLOW correct structural OR displayed OR skeletal formula ALLOW combination of formulae as long as unambiguous DO NOT ALLOW molecular formulae ALLOW correct names for A, B and C For B accept diester For C, IGNORE n OR brackets (even if wrong); ALLOW solid side bonds Minimum is one correct repeat unit. Polymer must be open at both ends Total<br />

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