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OCR A AS Jun 2016 Paper 2 Q6
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![This question is about the properties and reactions of butan-2-ol. 14 OH Some properties of butan-2-ol are listed in the table. Melting point Boiling point 115 C 99.5 C (a) Why is butan-2-ol classified as a secondary alcohol?[1] (b) The shape around the oxygen atom in butan-2-ol is non-linear. Predict the COH bond angle and explain this shape. bond angleexplanation[4] (c) Butan-2-ol can be oxidised by heating with an oxidising agent. (i) Write an equation for the reaction. Use [O] to represent the oxidising agent and show the structure of the organic product. [2]OCR 2016<br />
(ii) A student plans to carry out this oxidation using the apparatus shown in the diagram. 15 Give one reason why the apparatus is not suitable and describe a more suitable way of carrying out this oxidation.[2] (d) 20.2 g of butan-2-ol is reacted with excess sodium bromide and sulfuric acid. CH3CH(OH)CH2CH3 + NaBr + H2SO4 CH3CHBrCH2CH3 + NaHSO4 + H2O 25.2 g of CH3CHBrCH2CH3 is formed. Calculate the percentage yield of CH3CHBrCH2CH3. percentage yield =% [3]OCR 2016 Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_QP_-_Paper_2_OCR_Chemistry_A_AS-Level_6-0.jpg)
![Answer Mark scheme Marks AO element AO1.1 Guidance ALLOW alcohol/ hydroxyl/functional group for OH June 2016 H032/02 Question 6 (a) (b) The OH group is attached to a carbon that is attached to one hydrogen atom OR The OH group is attached to a carbon that is attached to two C atoms/ alkyl groups/R groups104.5(oxygen atom) has two bond pairs and two lone pairs1 Bonded pairs/lone pairs/electron pairs repelLone pairs repel more than bonding pairsNOTE: Lone pairs repel more than bonding pairs would gain the last two marking points AO1.1 AO1.1 AO2.1 AO2.1 ALLOW 104105 ALLOW lp and bp ALLOW bonding regions for bond pairs IGNORE bonds repel / electrons repel DO NOT ALLOW atoms repel ALLOW alternative phrases/words to repel e.g. push apart ALLOW molecular formulae: C4H10O and C4H8O ALLOW C4H9OH ALLOW C2H5 for CH3CH2 ALLOW correct structural OR displayed OR skeletal formulae OR a combination of above as long as unambiguous IGNORE vague answers about health and safety ALLOW alcohol for butan-2-ol ALLOW ketone for butanone DO NOT ALLOW the product or reactant. DO NOT ALLOW distillation DO NOT ALLOW any reference to closed system. (c) (i) Equation CH3CH(OH)CH2CH3 + [O]CH3COCH2CH3 + H2OStructure of product could be allowed from equation CH3COCH2CH3(ii) Butan-2-ol/butanone is flammable OR Butan-2-ol/butanone is volatile/low boiling point OR Butan-2-ol /butanone will evaporate/boil away(Heat under) reflux OR a description of reflux with vertical condenser and a round bottomed or pear shaped flask with source of heat.AO2.72 AO3.42 17<br />
H032/02 Question (d) Answer Mark scheme Marks FIRST CHECK ANSWER ON THE ANSWER LINE IF answer = 67.4% award all 3 marks for calculation n(butan-2-ol) (m/M) = 20.2/74 OR = 0.273 moln(2-bromobutane (m/M) = 25.2/136.9 OR = 0.184 mol% yield = (0.184/0.273)100) = 67.4%1 1 AO element AO1.1 AO2.4 AO2.4 June 2016 Guidance If there is an alternative answer, check to see if there is any ECF credit possible ALLOW 3 SF: 0.273 up to calculator value of 0.272972973 correctly rounded ALLOW 3 SF: 0.184 up to calculator value of 0.184075967 correctly rounded ALLOW (25.2/137) = 0.183941605 ALLOW 67% if evidence shows 67.4% in answer ALLOW 67.4% up to calculator value correctly rounded. Common ECFs (2 marks) Incorrect Mr resulting in incorrect moles of butan-2-ol or 2-bromobutane ALLOW calculation in mass for 2nd and 3rd marks m(CH3CHBrCH2CH3) = 0.273136.9 = 37.4 g % yield = (25.2/37.4)100 = 67.4% Total 12 18<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_MS_-_Paper_2_OCR_Chemistry_A_AS-Level_6-0.jpg)
