AQA Jun 2017 Paper 2 Q6 (with explained solutions) |

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AQA Jun 2017 Paper 2 Q6

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0 6 0 6 . 1 10 2-Methylpropan-1-ol can be prepared by reacting 1-bromo-2-methylpropane with dilute aqueous sodium hydroxide.[3 marks] Name and outline the mechanism for this reaction. Name of mechanism Mechanism 0 6 . 2 When 2.0 cm3 of 1-bromo-2-methylpropane (Mr = 136.9) were reacted with an excess of sodium hydroxide, 895 mg of 2-methylpropan-1-ol (Mr = 74.0) were obtained. The density of 1-bromo-2-methylpropane is 1.26 g cm3 Calculate the percentage yield for this reaction. [3 marks] Percentage yield *10* IB/M/Jun17/7404/2<br />
110 6 . 3 When 1-bromo-2-methylpropane reacts with hot, concentrated ethanolic potassium hydroxide rather than dilute aqueous sodium hydroxide, a different product is formed. Name this organic product and name the mechanism for this reaction. [2 marks] Name of organic product Name of mechanism Turn over for the next question *11* Turn overIB/M/Jun17/7404/2<br />

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MARK SCHEMEAS-LEVEL CHEMISTRY7404/2JUNE 2017 Question Marking Guidance Mark Comments 06.1 M1 nucleophilic substitution M2 curly arrow from lone pair on O of OH to C of C-Br M3 curly arrow from C-Br bond to the Br Penalise M3 for formal charge on C and/or Br of C-Br or incorrect partial charges on C-Br Max 1 out of 2 for M2 & M3 for incorrect reactant or product (ignore poorly drawn bond from C to OH group in product if shown) For SN2 penalise M2 for any additional arrow(s) on NaOH penalise M3 for any additional arrow(s) to/from the Br to/from anything else If SN1 mechanism given (loss of Br first followed by attack by OH) then: M2 curly arrow from C-Br bond to the Br M3 curly arrow from lone pair on O of OH to positive C atom of correct carbocation penalise M2 for any additional arrow(s) to/from the Br to/from anything else penalise M3 for any additional arrow(s) on NaOH If curly arrows represent an attempt at an elimination mechanism, cannot score M2 or M3 18 of 26<br />
MARK SCHEMEAS-LEVEL CHEMISTRY7404/2JUNE 2017 Question Marking Guidance Mark Comments 06.2 M1 Amount 1-bromo-2-methylpropane (= (2 x 1.26) / 136.9 = 2.52/136.9) = 0.0184 mol M2 mass of 2-methylpropan-1-ol expected (= 0.0184 x 74.0) = 1.36 g M3 % yield = 100 x (0.895/1.36) = 65.7% (65-67%) 06.3 M1 methylpropene M2 elimination Correct answer scores 3 marks; answer to at least 2sf and any individual marks for M1/2 should be at least 2sf; answers that are a factor of 10x out score 2; Allow ECF through the question Alternative method: M2 amount of 2-methylpropan-1-ol produced = 0.895/74.0 = 0.0121 mol M3 % yield = 100 x (0.0121/0.0184) = 65.7% (65-67%) Allow 2 marks for 82.7-83% (comes from starting with 2 g not 2.52 g), with answers that are a factor of 10x out from this scoring 1 M1 Do not allow any names with numbers for the position of the double bond. Allow 2-methylpropene but no other answer Ignore any drawn mechanism M2 allow base (or basic) elimination but no other answer 19 of 26<br />

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