OCR A AS Jun 2016 Paper 2 Q7 (with explained solutions) |

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OCR A AS Jun 2016 Paper 2 Q7

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7* Organic compound C has the following percentage composition by mass: C, 54.5%; H, 9.1%; O, 36.4%. The infrared spectrum and mass spectrum of compound C are shown below. 16 100 transmittance (%) 50 0 4000 3000 2000 1500 wavenumber / cm1 1000 500 100 80 60 40 20 relative intensity 10 20 30 40 50 m / z 60 70 80 90 In the mass spectrum, a secondary carbocation is responsible for the peak with the greatest relative intensity.OCR 2016<br />
Identify compound C. 17 In your answer you should make clear how your conclusion is linked to all the evidence.[6]OCR 2016 END OF QUESTION PAPER<br />

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H032/02 Question 7 Mark scheme June 2016 Answer Please refer to marking instructions on page 4 of mark scheme for guidance on how to mark this question. Level 3 (56 marks) A comprehensive description with all three scientific points explained thoroughly. C identified as a carboxylic acid containing four carbon atoms linked to the peak in the mass spectrum at 43. The explanation makes use of all the evidence including the secondary carbocation in justifying the correct structure of C. Level 2 (34 marks) Attempts all three scientific points but explanations may be incomplete. OR Explains two scientific points thoroughly with few omissions. The analysis is clear and includes some interpretation of IR and MS peaks. Level 1 (12 marks) A simple explanation based on at least two of the main scientific points. OR Explains one scientific point thoroughly with few errors. The analysis is communicated in an unstructured way and includes interpretation of peaks from IR OR MS spectrum 0 marksNo response worthy of credit. Total Marks AO element AO3.12 AO3.12 AO3.22 Guidance LOOK ON THE SPECTRA for labelled peaks. Indicative scientific points may include: 1. Molecular formula Element C H O % mass 54.5 9.1 36.4 Ar 12 1 16 moles 4.54 9.1 2.28 ratio 2 4 1empirical formula = C2H4Omolecular ion peak m/z or Mr = 88molecular formula = C4H8O2 2. Infrared spectrumpeak at 25003500 (cm1) is OHpeak at 1630-1820 (cm1) is C=OC is a carboxylic acid ALLOW stated values within the ranges above IGNORE references to CO peaks 3. Identifying the carboxylic acid (CH3CH2CH2COOH OR (CH3)2CHCOOH)Mass spectrum peak at m/z = 43 = C3H7(+)secondary carbocation: CH3C+HCH3compound C: (CH3)2CHCOOH IGNORE name of carboxylic acid if structure given 19<br />

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