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OCR A Jan 2013 Paper 4 Q1
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![Answer all the questions. 1 Pyruvic acid, shown below, is an organic compound that has a smell similar to ethanoic acid. It is extremely soluble in water. OH H3C pyruvic acid (a) Explain why pyruvic acid is soluble in water. Use a labelled diagram to support your answer.[2] (b) Pyruvic acid can be prepared in the laboratory by reacting propane-1,2-diol with excess acidified potassium dichromate(VI). The reaction mixture is heated under reflux. Write an equation for this oxidation. Use [O] to represent the oxidising agent and show structural formulae for organic compounds.OCR 2013 [2]<br />
(c) Pyruvic acid can also be reduced by NaBH4 to form CH3CH(OH)COOH. Outline the mechanism for this reduction. Use curly arrows and show relevant dipoles. (d) Compound A, shown below, is a structural isomer of pyruvic acid. [4] OH compound A Describe a chemical test that could be carried out in a laboratory to distinguish between samples of pyruvic acid and compound A. Your answer should include reagents, observations, the type of reaction and the organic product formed. In your answer, you should use appropriate technical terms, spelled correctly.[3]OCR 2013 Turn over<br />
(e) Compound B is an organic compound used to make some cosmetics. Compound B contains C, H and O only. Elemental analysis shows that B has the percentage composition by mass: C, 55.81%; H, 7.02%; O, 37.17%. The mass spectrum of compound B is shown below. 100 relative intensity 80 60 40 20 10 20 30 40 50 60 m / z 70 80 90 100 110 120 (i) Determine the molecular formula of compound B. Show all of your working. molecular formula of compound B =[2]OCR 2013<br />
(ii) Compound B is an E-stereoisomer. Compound B effervesces with aqueous Na2CO3 to form organic compound C. Compound B decolourises Br2 to form compound D. Compound B polymerises to form polymer E. In the boxes below:draw structures for compounds B, C and D.draw one repeat unit for polymer E. compound B compound C compound D one repeat unit of polymer E [4] [Total: 17] Turn overOCR 2013<br />
BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGEOCR 2013<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_4_QP_JAN13_question_1-0.jpg)
![F324 Mark Scheme January 2013 Question 1 (a) M1 EITHER in words: Answer (pyruvic acid forms) hydrogen bonds with water OR correctly labelled diagram showing hydrogen bond between pyruvic acid and water (cid:57) M2 diagram showing dashed/dotted line between H+ in COOH and lone pair of electrons on O in H2O H3C (cid:71)(cid:14) OR diagram showing dashed/dotted line between H+ in H2O and lone pair of electrons on O of OH in COOH (cid:57) (b) CH3CH(OH)CH2OH + 3[O]CH3COCOOH + 2H2O H3C (cid:71)(cid:14) H four correct formulae (cid:57) balanced (cid:57) Marks Guidance FOR M1 only: if use diagram ALLOW a labelled hydrogen bond to O in C=O FOR M2 only: IGNORE a hydrogen bond to C=O, i.e. C=O - - - HO IGNORE bond angles Diagram does not need to show all of pyruvic acid (IGNORE if wrong so allow ethanoic acid) but must have minimum of COOH MIMIMUM requirement is a H+ (on acid or water) and a lone pair on O (in acid or water) involved in a hydrogen bond ie IGNORE - ALLOW correct structural OR displayed OR skeletal formulae OR combination of above as long as unambiguous (IGNORE lack of brackets round 2 alcohol) DO NOT ALLOW molecular formulae IF propane1,3-diol used score 0<br />
F324 Mark Scheme January 2013 Question 1 (c) M1 H3C (cid:71)(cid:14) M2 (cid:71)(cid:16) Answer intermediate M3 COOH H3C COOH M4 M1: 1 mark for curly arrow from H to C of C=O (cid:57) M2: 1 mark for correct dipoles on C=O AND curly arrow from double bond to O(cid:71) (cid:57) M3: 1 mark for correct intermediate withcharge on O (cid:57) M4: 1 mark for curly arrow from O of intermediate to H in H2O AND curly arrow from the OH bond to the O in H2O: Do not need to show formation of OH Marks Guidance Curly arrow MUST start fromsign OR lone pair on H Lone pair does not need to be shown on H Lone pair does not need to be shown on O Curly arrow MUST start fromsign OR from lone pair on O of intermediate Lone pair does not need to be shown on O For M4, ALLOW mark for curly arrow from O of intermediate to H+ COOH H3C M4 H+<br />
F324 Mark Scheme January 2013 Question 1 (d) Answer (cid:57) Either: Use Tollens reagent AND correct reference to compound A being oxidised or Tollens reagent acts as oxidising agent (cid:57) Observation: silver mirror/precipitate/ppt/solid (cid:57) or: Use K2Cr2O7 AND H2SO4 AND correct reference to compound A being oxidised or K2Cr2O7 acts as oxidising agent Observation: turns (dark) green OR blue (cid:4) QWC oxidised/oxidized/oxidation/redox etc. must be spelled correctly at least ONCE (i.e. NOT oxidisation, oxidated) to score 1st mark UNLESS 2,4-DNP(H)/Bradys reagent is used, when condensation/additionelimination must be spelled correctly at least ONCE (cid:57) Guidance ALLOW AgNO3 in ammonia OR ammoniacal AgNO3 ALLOW redox reaction ALLOW black ppt OR grey ppt ALLOW Na2Cr2O7 OR Cr2O7 2 for K2Cr2O7 If formulae used, formulae must be correct ALLOW acidified dichromate If name given, ALLOW dichromate OR dichromate(VI) IGNORE reference to dilute/conc ALLOW H+ ALLOW KMnO4 and H2SO4 / acidified manganate(VII)/ permanganate / alkaline manganate(VII) AND correct reference to compound A being oxidised or KMnO4 acts as oxidising agent Observation: decolourised ALLOW Benedicts or Fehlings reagent/solution AND correct reference to compound A being oxidised or Benedicts or Fehlings acts as oxidising agent Observation: (brick) red ppt ALLOW 2,4-DNP(H)/Bradys reagent AND measure melting point of derivative AND state it is a condensation reaction/addition- elimination reaction Observation: orange/yellow/red precipitate ALLOW solid OR crystals OR ppt as alternatives for precipitate Marks<br />
January 2013 Guidance ALLOW correct structural OR displayed OR skeletal formulae OR combination of above as long as unambiguous ALLOW COO if used Tollens or Fehlings or Benedicts ALLOW correct unambiguous name: propan(e-1,3-)dioic acid IGNORE dipropanoic acid DO NOT ALLOW propan(e-1,3-)dicarboxylic acid if used 2,4-DNP(H): ALLOW correct hydrazone structure or name ALLOW (2,4-dinitrophenyl)hydrazone (derivative) Alternative method scores 2 marks: 0.0702/1 x 86 = 6; 0.3717/16 x 86 = 2; 0.5581/12 x 86 = 4 C4H6O2 answer alone worth 2 marks Answer Mark Scheme Marks F324 Question HOOCCH2COOH (cid:57) (e) (i) % mol ratio C 55.81% 4.65 2 H 7.02% 7.02 3 empirical formula = C2H3O (cid:57) molecular formula = C4H6O2 (cid:57) O 37.17% 2.32 1<br />
H3C Answer OH compound B (cid:57) Mark Scheme Marks January 2013 Guidance ALLOW correct structural OR displayed OR skeletal formulae OR combination of above as long as unambiguous eg COOH does not have to be displayed E/trans stereoisomer is needed For compound C, Br ONa H3C OH Br compound D (cid:57) F324 Question 1 (e) (ii) H3C compound C (cid:57) ALLOW If charges shown on both O and Na then both must be correct OR (covalent bond) DO NOT ALLOW ALLOW ECF for C and D if B is identified as one of the following three structures: CH3 OH OH CH3 OH<br />
Answer COOH CH3 one repeat unit of polymer E (cid:57) F324 Question Mark Scheme Marks January 2013 Guidance For polymer E, brackets not required IGNORE n Free rotation so CH3 can be shown at top, next to COOH IF more than one repeat unit has been drawn a single repeat unit MUST be identified by brackets or clear label The only polymers to ALLOW as ECF from incorrect B are: COOH CH3 COOH CH2 CH3 COOH Total 17<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_4_QP_JAN13_answer_1-0.jpg)
