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OCR A Jan 2010 Paper 4 Q2
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![2 Hydroxyethanal, HOCH2CHO, is sometimes referred to as the first sugar as it is the simplest possible molecule that contains both an aldehyde group and an alcohol group. A biochemist investigated some redox reactions of hydroxyethanal and found that several different products were produced. (a) The biochemist reacted hydroxyethanal with Tollens reagent. (i) State what the biochemist would see when hydroxyethanal reacts with Tollens reagent.[1] (ii) Write the structural formula of the organic product formed when hydroxyethanal reacts with Tollens reagent. (b) The biochemist also reacted hydroxyethanal with acidified dichromate by heating under reflux. [1] Write an equation for this oxidation. Use [O] to represent the oxidising agent. [2] (c) The biochemist then reduced hydroxyethanal using aqueous NaBH4. (i) Write the structural formula of the organic product.[1] (ii) Outline the mechanism for this reduction. Use curly arrows and show any relevant dipoles.OCR 2010 [4] [Total: 9] Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_4_QP_JAN10_question_2.jpg)
![F324 Question 2 (a) (i) silver mirror (cid:57) Expected Answers Mark Scheme Marks (ii) HOCH2COOH (cid:57) (b) HOCH2CHO + 3[O] (cid:111) HOOCCOOH + H2O reagents (cid:57) both products (cid:57) (c) (i) HOCH2CH2OH (cid:57) (ii) curly arrow from H- to C(cid:71)+ (cid:57) dipoles and curly arrow from C=O bond to O (cid:57) intermediate (cid:57) curly arrow from intermediate to H(cid:71)+ in H2O/ H+ and if H2O is used it must show the curly arrow from the OH bond to the O (cid:57) lone pairs are not essential 35 January 2010 Additional Guidance ALLOW Ag(s) OR Ag mirror OR precipitate OR ppt OR solid ALLOW brown OR black OR grey ALLOW CH2OHCOOH OR CH2OHCO2H OR HOCH2CO2H OR displayed OR skeletal formula OR HOCH2COO- DO NOT ALLOW C2H4O OR 2-hydroxyethanoic acid ALLOW displayed/skeletal formula/COOHCOOH (cid:57)(cid:57) if molecular formula used C2H4O2 + 3[O] (cid:111) C2H2O4 + H2O max = 1 (cid:57) Any correctly balanced equation for partial oxidation can score 1 mark (cid:57) HOCH2CHO + [O] (cid:111) HOCH2COOH OR HOCH2CHO + 2[O] (cid:111) OHCCOOH + H2O OR HOCH2CHO + [O] (cid:111) OHCCHO + H2O OR HOCH2CHO + 2[O] (cid:111) HOOCCHO + H2O ALLOW HO(CH2)2OH OR (CH2OH)2 OR skeletal formula OR displayed formula DO NOT ALLOW molecular formula (C2H6O2) ALLOW curly arrow to C even if dipole missing or incorrect ALLOW maximum of 3 marks if incorrect starting material is used See page 36 for detailed mechanismsAlternative 3 scores all 4 marks even though the intermediate is not shown<br />
F324 Alternative 1 Alternative 2 Alternative 3 Mark Scheme January 2010 HOH2C (cid:71)+ C HOH2C (cid:71)+ C (cid:71)- O (cid:71)- O H- - H - (cid:71) O (cid:71)+ (cid:71)- H O - H HOH2C (cid:71)+ C - (cid:71) O (cid:71)+ H - O HOH2C + H - O HOH2C or HOH2C (cid:71)+ C (cid:71)- H O H- products are not required Total 36<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_4_QP_JAN10_answer_2-0.jpg)
