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Edexcel Jan 2010 Paper 4 Q22
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![Mark Acceptable Answers Reject any reference to hydrogen bonding in ethanal just references to ethanol and ethanoic acid forming H bonds with water references to breaking covalent bonds Just ethanoic acid has more hydrogen bonds than ethanol Each mark is a stand alone mark. First mark: hydrogen bonds in both ethanoic acid and ethanol OR no hydrogen bonds in ethanal (1) Second mark: hydrogen bonds are stronger than van der Waals/ dipole-dipole/London/dispersion/ induced dipole / permanent dipole /intermolecular forces (in ethanal) OR hydrogen bonds are the strongest/strong intermolecular forces (1) Third mark: ethanoic acid has more electrons/ethanoic acid has the most electrons OR ethanoic acid is dimeric OR ethanoic acid forms dimers OR description of ethanoic acid dimers (N.B. In the context of dimerisation, ignore statement that ethanoic acid forms two hydrogen bonds per molecule) OR ethanoic acid is more polar because of having more oxygen atoms (1) Question Number 22 (a) QWC<br />
Acceptable Answers Reject (Test): 2,4-dinitrophenylhydrazine /Bradys reagent/2,4-dnp/ 2,4-DNP/2,4-DNPH (1) (Result):yellow precipitate /orange precipitate /red precipitate ALLOW: solid or crystals in lieu of precipitate (1) Result mark for result CQ on correct reagent (or a near miss reagent (e.g. 2,4-DHPN)) 1,2-DNP etc/ hydrazine / /2,4- dinitrophenolhydrazine /2,4- dinitrophenylhydrazone Acceptable Answers Reject Mark Mark acidified potassium dichromate(VI) / manganate(VII) (0) iodoform reaction (0) just red due to Cu +/ 3+ red solid due to Cu(0) (Warm with) Fehlings (solution) / Benedicts (solution) (1) red precipitate/brown precipitate/brick-red precipitate (1) ALLOW solid ALLOW red Cu2O ALLOW yellow/orange solid for Benedicts test Penalise omission of solid once only in parts (b)(i) and (b)(ii) OR (Warm with) Tollens (reagent) (1) silver (mirror)/black(solid) (1) (N.B. here, solid not required) OR (Warm with) ammoniacal silver nitrate (solution) (1) silver (mirror)/ black / dark-grey (solid) (1) (N.B. here, solid not required) 2nd mark CQ on correct reagent or a near miss Penalise omission of solid once only in (b)(i) and (b)(ii) Question Number 22 (b)(i) Question Number 22 (b)(ii)<br />
Mark Question Number 22 (c)(i) Acceptable Answers Reject arrow from N in CN- (1) IGNORE any dipoles shown Check curly arrows are all double-headed in mechanism. (If all arrows are single-headed, can only score intermediate mark.) Accept: arrow to an H+ instead of an H-CN for third mark. [It is not necessary to show the lone pairs.] IGNORE any equations which generate CN- ions Question Number 22 (c)(ii) Mark Acceptable Answers Reject With HCN alone, insufficient CN OR KCN provides (sufficient) CN OR KCN increases the concentration of CN ALLOW nucleophile instead of CN IGNORE any subsequent comments about the role of the CN- ion Just HCN is a weak acid OR HCN is too weak a nucleophile<br />
Question Number 22 (c)(iii) QWC Mark Acceptable Answers Reject These are stand alone marks First mark: attack from both sides OR attack from above and below (1) Second mark: (gives) racemic mixture / (gives) equal amounts of each isomer / (gives) equal amounts of each enantiomer (1) attack on a (planar) carbocation OR attack on a (planar) intermediate OR SN1 OR SN2 planar product<br />](https://learnah.org/wp-content/uploads/2018/08/January_2010_MS_-_Unit_4_Edexcel_Chemistry_A-level_22-0.jpg)
