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OCR A Jun 2016 Paper 2 Q7
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![7 A student was provided with a mixture of two structural isomers. Each isomer has the percentage composition by mass C, 29.29%; H, 5.70%; Br, 65.01%. The relative molecular mass of each isomer is less than 150. 21 (a) Determine the structures of the two structural isomers. Show your working. In your answer you should link the evidence with your explanation.[5]OCR 2016 Turn over<br />
22 (b) The student heats the mixture of the two structural isomers from (a) under reflux with aqueous sodium hydroxide to form two compounds, E and F. The student separates the two compounds. Compound E is heated under reflux with acidified potassium dichromate(VI) to form compound G, which gives the infrared spectrum below. 100 transmittance (%) 50 0 4000 3000 2000 1500 wavenumber / cm1 1000 500 (i) Analyse the information and spectrum to determine the structures of E, F and G. Include an equation for the formation of G from E. In your answer you should link the evidence with your explanation.OCR 2016<br />
23[6] (ii) Compound G is heated with compound F in the presence of a small amount of concentrated sulfuric acid to form organic compound H. Draw the structure of the organic compound H. END OF QUESTION PAPER [2] [Total: 13]OCR 2016<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_2_QP_JUN16_question_7-0.jpg)
![F322 Question (a) Mark scheme June 2016 Answer 3 marks Empirical/molecular formula Mole ratio C : H : Br is 2.44 : 5.70 : 0.814 (cid:57) (Empirical formula) = C3H7Br (cid:57) QWC (Molecular formula) = C3H7Br AND relative mass linked to 150 evidence (cid:57) Structural isomers CH3CH2CH2Br (cid:57) CH3CHBrCH3 (cid:57) 2 marks Marks Guidance 5.70 : 1.0 65.01 79.9 29.29 : 12.0 ANNOTATE ANSWER WITH TICKS AND CROSSES ALLOW Evidence could include a calculation of the relative mass of C3H7Br as 122.9 linking to Mr being less than 150 ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) DO NOT ALLOW missing H atom(s) in a displayed formula for one structure but ALLOW missing H atoms in subsequent structure Note: structures from an incorrect molecular formula will be credited on their merits. Please consult TL for advice on how to mark the subsequent parts of this question 29<br />
F322 Question (i) (b) Answer Infrared for G 1700 cm1 AND C=O/carbonyl group (cid:57) (broad) 23003600 cm1 AND OH in carboxylic acid (cid:57) 2 marks 3 marks Structures CH3CH2CH2OH (cid:57) CH3CHOHCH3 (cid:57) CH3CH2COOH (cid:57) Mark scheme June 2016 Marks Guidance ANNOTATE ANSWER WITH TICKS AND CROSSES LOOK ON THE SPECTRUM for labelled peaks which can be given credit ALLOW ranges from Data Sheet: C=O within range 16401750 cm1; (broad) OH within range 25003300 cm1 ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) ALLOW CH3CH2CO2H for carboxylic acid IGNORE names IGNORE labels DO NOT ALLOW missing H atom(s) in a displayed formula for one structure but ALLOW missing H atoms in subsequent structures ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above in equation Equation for formation of G C3H8O + 2[O] (cid:111) C3H6O2 + H2O (cid:57) 1 mark 30<br />
Answer Mark scheme Marks June 2016 Guidance ANNOTATE ANSWER WITH TICKS AND CROSSES ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) ALLOW C2H5CO2CH(CH3)2 IF there is one bond and its H missing from the correct ester award 1 mark F322 Question (ii) (b) CH3CH2COOCH(CH3)2 (cid:57)(cid:57) 2 marks for correct ester. Award 1 mark for: OR Ambiguous ester: CH3CH2COOCH2CH2CH3 CH3CH2COOC3H7 (cid:57) Total 13 31<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_2_QP_JUN16_answer_7-0.jpg)
