Edexcel Jun 2014 Paper 4 Q10 (with explained solutions) |

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Edexcel Jun 2014 Paper 4 Q10

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10 A flow chart for making 2-hydroxy-2-methylbutanoic acid from butan-2-ol is shown below. CH3CH2CH(OH)CH3 Step 1 CH3CH2COCH3 Step 2 CH3CH2C(CH3)(OH)CN Step 3 CH3CH2C(CH3)(OH)COOH (a) (i) Give the reagents and conditions for Step 1. (2)(ii) Butanone is formed in Step 1. Give a chemical test to identify the carbonyl group and a further test to show O the presence of the H3CC For both tests, give the observations that you would make. group. (4) Carbonyl groupO H3CC group12 *P42972A01224*<br />
(b) (i) In Step 2, butanone undergoes an addition reaction with HCN in the presence of CN ions. Give the mechanism for this reaction. *(ii) By considering the mechanism of the reaction, explain why the addition of hydrogen cyanide to butanone gives a solution which has no effect on the plane of polarization of plane-polarized light. (3) (3)(c) (i) Suggest the type of reaction occurring in Step 3. (1)(ii) Explain why the presence of the alcoholic hydroxyl group cannot be confirmed in the infrared spectrum of 2-hydroxy-2-methylbutanoic acid. (1)*P42972A01324* 13 Turn over<br />
(iii) The hydrogen of the alcohol group in 2-hydroxy-2-methylbutanoic acid can be identified by a single peak in the nmr spectrum. Give the chemical shift you would expect for this peak. (1)(iv) Explain why, in high resolution nmr, the peak due to the hydrogens of the 2-methyl group in 2-hydroxy-2-methylbutanoic acid is a singlet. (1)(d) Molecules of 2-hydroxy-2-methylbutanoic acid react together to form a condensation polymer. Draw a displayed formula for this polymer, showing two repeating units. (2) (Total for Question 10 = 18 marks) 14 *P42972A01424*<br />

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Correct Answer Question Number 10(a)(i) Sodium/potassium dichromate ((VI)) and (Dilute/concentrated) sulfuric acid OR correct formulae / H+ and Cr2O7 ALLOW H+ and Cr2O7 2/acidified dichromate((VI)) (1) 2 Reflux/distil Ignore heat, warm, and boil alone. ALLOW Just under reflux Just under distillation (1) 2 in first part Second mark depends on mention of dichromate/Cr2O7 OR KMnO4 and acid with heat (1) Mark Reject Hydrochloric acid 6CH0401 1406<br />
Question Number 10 (a)(ii) Correct Answer Carbonyl groupaddition of 2,4-dinitrophenylhydrazine / 2,4-DNP(H) / Bradys reagent (1) to give yellow/orange/red precipitate/ppt/ppte/solid/crystals ALLOW recognisable spelling e.g., percepitate (1) Mark Reject 2-DNP/4DNP Just DNP Brick red ppt CH3C=O reaction with iodine in alkali/NaOH/KOH/OH- ALLOW Iodoform/tri-iodomethane/haloform AND reaction/test to form (pale) yellow / cloudy precipitate/solid/crystals (1) (1) Ignore references to smell Ignore heat in either part Note In both cases result mark depends on test being recognisably correct even if it did not score a mark Examples: DNP gives yellow ppt Iodine test gives yellow pptTests for aldehydes with correct results, no marks 6CH0401 1406<br />
Question Number 10 (b)(i) Correct Answer Arrow (from carbon) of CN- to carbon of C=O AND Arrow from part of C=O double bond to oxygen ALLOW Two steps via a charged canonical form (1) Intermediate anion with C-CN bond. (1) Arrow from resulting O- to hydrogen of HCN/H+/H2O (1) Note Arrow directions must be correct to score each mark Penalise half-headed arrows each time in both parts ALLOW skeletal formulae. Mark Reject CN without negative charge C-NC bond 6CH0401 1406<br />
Question Number 10 (b)(ii) Question Number 10 (c)(i) Mark Reject Butanone/molecule/it is planar C=O is planar Carbonyl bond is planar Intermediate is planar Correct Answer Forms a racemic mixture (1) Because bonds around C=O are planar OR Carbonyl group/reaction site is (trigonal) planar OR Bonds around carbonyl carbon are planar (1) Cyanide can attack from either side / above or below (1) Correct Answer (Acid) hydrolysis OR Alkaline hydrolysis followed by acidification Reject Hydration Mark 6CH0401 1406<br />
Question Number 10 (c)(ii) Question Number 10 (c)(iii) Question Number 10 (c)(iv) Correct Answer The O-H absorptions for alcohol and carboxylic acid overlap. OR OH absorption for an acid is very broad OR Quote data booklet values which must show some overlap, to include 3300 to 3200. ALLOW OH absorptions similar/the same. Reject Mark Just both have OH groups Just two OH groups present Correct Answer (Chemical shift ) 2.0 - 4.0 (ppm) / any value within this range ALLOW Correct number followed by , eg 3 Reject Correct Answer There is no hydrogen atom/proton on the adjacent/neighbouring carbon atom ALLOW No adjacent/neighbouring hydrogens/protons Reject Mark Mark 6CH0401 1406<br />
Question Number 10 (d) Correct Answer Reject Mark Ester linkage (1) Rest of molecule (1) ALLOW Attached chains as structural formulae Ignore n or other numbers outside bracket Total for Question 10 = 18 marks 6CH0401 1406<br />
2- + 2I-2SO4 Correct Answer S2O8 ALLOW multiples Ignore state symbols even if incorrect 2- + I2 Question Number 11 (b)(i) Blue/black /blue-black Correct Answer OR Colourless to blue-black/ blue/black Correct Answer The mixture would change colour/ go blue/black /blue-black immediately/straight away ALLOW too quick(ly)/too early quicker no time delay Correct Answer (As quickly as iodide reacts to form iodine it is) reduced/turned back to iodide by the thiosulfate ions ALLOW Persulfate reacts with thiosulfate first. OR Iodine reacts with thiosulfate. Question Number 11(a) Question Number 11 (b)(ii) Question Number 11 (b)(iii) Reject Reject Purple Reject Mark Mark Mark Reject Mark 6CH0401 1406<br />

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