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OCR A Jun 2012 Paper 2 Q2
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![2 Epoxyethane, C2H4O, is a synthetic intermediate that is used to make ethane-1,2-diol and some polymers. The structure of epoxyethane is shown below. (a) The controlled catalysed reaction of ethene with oxygen forms epoxyethane as the only product. (i) Write the equation for this reaction. (ii) When burnt in excess oxygen, ethene completely combusts. Write the equation for the complete combustion of ethene. [1][1] (b) Epoxyethane reacts with water in the presence of an acid catalyst to form ethane-1,2-diol. H2O OH OH The mechanism for this reaction is shown below. step 1 step 2OCR 2012 O+ OH OH H+ OH step 3 step 4 OH + O<br />
(i) Draw dipoles on the carbon and oxygen atoms on the displayed formula of epoxyethane. (ii) The mechanism uses the curly arrow model. What does a curly arrow represent? [1][1] (iii) What type of bond fission occurs in step 2? Explain your answer.[2] (iv) How can you tell that water is behaving as a nucleophile in step 3?[1] (v) How does the mechanism show that H+ ions act as a catalyst in this reaction? Refer to the steps in the mechanism in your answer.[1] (vi) Epoxyethane reacts with methanol, CH3OH, to form a compound with the molecular formula C3H8O2. Suggest the structure of this compound.OCR 2012 [1] Turn over<br />
(c) Ethane-1,2-diol is much less volatile than ethanol. Suggest why.[2] (d) Ethane-1,2-diol reacts with an excess of ethanoic acid, CH3COOH, in the presence of an acid catalyst. A compound is formed with the molecular formula C6H10O4. Draw the structure of this compound. (e) Ethane-1,2-diol reacts with warm acidified potassium dichromate(VI). A number of different organic products are formed. Draw the displayed formulae of two of these organic products. [2] [2] [Total: 15]OCR 2012<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_2_QP_JUN12_question_2-0.jpg)
![F322 Question 2 (a) (i) 2C2H4 + O2 (cid:198) 2C2H4O (cid:57) Answer Mark Scheme Marks June 2012 Guidance ALLOW molecular formulae OR correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) ALLOW correct multiples, including fractions, of this equation IGNORE state symbols DO NOT ALLOW [O] ALLOW molecular formulae OR correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) ALLOW correct multiples of this equation IGNORE state symbols DO NOT ALLOW [O] Only one carbon atom needs to have the correct partial charge DO NOT ALLOW partial charges on hydrogen atoms ALLOW movement of a lone pair OR movement of a bond ALLOW movement of two electrons MARK INDEPENDENTLY ALLOW one atom gets none of the bonded electrons DO NOT ALLOW both electrons go to a molecule DO NOT ALLOW makes a positive and a negative ion because in this example this is not true ALLOW donates a lone pair DO NOT ALLOW it donates electrons ALLOW H+ ion is used at the start AND made at the end IGNORE overall H+ is not used up in the mechanism (ii) C2H4 + 3O2 (cid:198) 2CO2 + 2H2O (cid:57) (cid:57) (b) (i) (cid:71)+ C (cid:71)- (ii) Movement of an electron pair (cid:57) (iii) (iv) (v) Heterolytic (cid:57) Both electrons (in the bond) go to the same atom OR (bond breaks) to make a cation and (a lone pair on the oxygen atom) OR bond pair becomes a lone pair on oxygen (cid:57) It donates a pair of electrons (cid:57) idea that H+ ion is used in step 1 AND made in step 4 (cid:57) 10<br />
F322 Question 2 (vi) (b) (c) (d) Mark Scheme June 2012 Marks Guidance ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) eg CH2OHCH2OCH3 ALLOW vertical bond to any part of the OH or OCH3 group DO NOT ALLOW formula with horizontal HO OR OH DO NOT ALLOW formula with horizontal CH3O OR OCH3 ALLOW has more hydroxyl groups OR has more hydroxy groups OR has more alcohol groups Ethane-1,2-diol has two OH groups is NOT sufficient but ALLOW ethane-1,2-diol has two OH groups and ethanol has one DO NOT ALLOW it has hydroxide (ions) ALLOW more hydrogen bonds (between ethane-1,2-diol molecules) IGNORE hydrogen bonds with water ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) ALLOW ester shown as all the atoms OR as COOC OR CH2OOC OR CH2OCOC IGNORE molecular formula Answer (cid:57) Ethane-1,2-diol has more OH groups (than ethanol) (cid:57) Stronger hydrogen bonding (between ethane-1,2-diol molecules) (cid:57) One ester linkage drawn despite the rest of the structure (cid:57) Correct structure for example CH3COOCH2CH2OOCCH3 OR H (cid:57) 11<br />
F322 Question 2 (e) Any two from: (cid:57)(cid:57) Answer Mark Scheme Marks C O O H O H O H June 2012 Guidance Mark incorrect answers first (cid:120) If one incorrect answer maximum of 1 mark (cid:120) If two incorrect answers award 0 marks ALLOW OH instead of OH ALLOW vertical bond to any part of the OH DO NOT ALLOW formula with horizontal HO OR OH but ALLOW ECF if both displayed formulae are drawn this way ALLOW one mark if two correct structural OR skeletal formula OR mixture of the above (as long as unambiguous) are drawn Total 15 12<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_2_QP_JUN12_answer_2-0.jpg)
