AQA Jun 2017 Paper 2 Q3 (with explained solutions) |

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AQA Jun 2017 Paper 2 Q3

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0 3 . 1Compounds A, B and C all have the molecular formula C5H10 A and B decolourise bromine water but C does not. B exists as two stereoisomers but A does not show stereoisomerism. Use this information to deduce a possible structure for each of compounds A, B and C and explain your deductions. State the meaning of the term stereoisomers and explain how they arise in compound B. [6 marks] *05* Turn overIB/M/Jun17/7404/2<br />

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MARK SCHEMEAS-LEVEL CHEMISTRY7404/2JUNE 2017 Ques 03 Marking Guidance Mark Comments This question is marked using levels of response. Refer to the Mark Scheme Instructions for Examiners for guidance on how to mark this question. Level 3 (5- 6 marks) All stages are covered, three correct structures are given and each stage is generally correct and virtually complete. Answer communicates reasoning coherently and shows a logical progression through the identification of structures including explaining about stereoisomerism. Level 2 (3- 4 marks) Two stages are covered or parts of three stages (if two stages are covered, they must be complete for 4 marks) Level 1 (1- 2 marks) One stage covered or parts of two stages (if one stage is covered, it must be complete for 2 marks) Level 0 (0 marks) No relevant correct chemistry to warrant a mark. Indicative chemistry content Stage 1deduces which compounds are saturated/unsaturated 1a states that A & B are unsaturated / do contain C=C / alkenes (this can be obtained from the structures) 1b as they decolourise bromine water 1c states that C is saturated / does not contain C=C / is (cyclo)alkane (this can be obtained from the structures) 1d as it does not decolourise bromine water Stage 2deduces the structures 2a suggests suitable name/structure for Apent-1-ene,2-methylbut-1-ene,3-methylbut-1-ene,2-methylbut-2-ene 2b B = pent-2-ene (name/structure) 2c suggests a suitable name/structure of C (cyclopentane, methylcyclobutane, any dimethylcyclopropane) Stage 3can explain the stereoisomerism 3a explains what stereoisomerism is in terms of molecules with the same structural formula but a different arrangement of atoms/bonds/groups in space 3b explains how it arises by discussing that C=C cannot rotate, 3c explains how it arises by discussing that each C in C=C has two different groups (ignore reference to Mr in this context) or by drawing the E and Z isomers of B Notecompounds may be identified by name or structure (but if both given and there is error in one, then award lower mark in whichever level the answer fits, i.e. it penalises the mark within a level, but not the overall level itself) 14 of 26<br />

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