OCR A Jun 2013 Paper 2 Q3 (with explained solutions) |

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OCR A Jun 2013 Paper 2 Q3

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3 Compound I is found in biodiesel. It has the skeletal formula shown below. (a) Name the two functional groups that are present in a molecule of I.[2] (b) Why is compound I unsaturated?[1] (c) A sample of compound I is shaken with aqueous bromine. What colour change would you see? fromto[1] (d) Compound J is a stereoisomer of compound I. (i) What is meant by the term stereoisomers?[1] (ii) Draw or describe how the structure of J differs from that of I.[1]OCR 2013<br />
(e) A student determined the enthalpy change of combustion for compound I. In her experiment, 1.34 g of compound I was used to heat 50.0 g of water. The temperature of the water changed from 20.2 C to 54.0 C. (i) What is meant by the term enthalpy change of combustion, Hc?[2] (ii) Calculate the energy released, in kJ, in the students experiment. The specific heat capacity of water is 4.18 J g1 K1. energy =kJ [2] (iii) The molecular formula of compound I is C17H32O2. Calculate the amount, in moles, of compound I used by the student. (iv) Calculate the enthalpy change of combustion of compound I. amount =mol [2]OCR 2013 Turn over Hc =kJ mol1 [3]<br />
(v) The student noticed that compound I burnt with a yellow flame and produced black smoke. Suggest an explanation for these observations.[1] (f) Some scientists believe that we should use more biofuels such as biodiesel and bioethanol. Bioethanol is made by the fermentation of plant sugars such as glucose. Write the equation for the fermentation of glucose to make ethanol and state two essential conditions for this fermentation. equationessential conditions[3] [Total: 19]OCR 2013<br />

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Answer Mark Scheme Marks F322/01 Question 3 (a) alkene (cid:57) ester (cid:57) (b) (c) contains a C=C bond (cid:57) (from) orange (to) colourless (cid:57) (d) (i) Same structural formula AND different arrangement (of atoms) in space OR different spatial arrangement (cid:57) June 2013 Guidance ALLOW carboncarbon double bond OR a C-C double bond A double bonded carbon is not sufficient C=C is not sufficient Carbon-carbon multiple bond is not sufficient Ketone / carbonyl / aldehyde / carboxylic acid contradicts the ester mark Contains a double bond is not sufficient Carbon-carbon multiple bond is not sufficient DO NOT ALLOW contains a C=O bond ALLOW shades of orange OR yellow OR brown ALLOW orange to decolourised DO NOT ALLOW red alone DO NOT ALLOW any response that includes precipitate OR solid, irrespective of colour DO NOT ALLOW clear for colourless ALLOW have the same structure/displayed formula/skeletal formula DO NOT ALLOW same empirical formula OR same general formula Stereoisomers have the same formula or molecular formula is not sufficient Different three dimensional arrangement is not sufficient Reference to E/Z isomerism or optical isomerism is not sufficient 12<br />
F322/01 Question (ii) (d) Mark Scheme Marks Answer (cid:57) (e) (i) (Enthalpy change that occurs) when one mole of a substance (cid:57) completely combusts OR reacts fully with oxygen (cid:57) 13 June 2013 Guidance Any writing must not contradict the diagram IGNORE any other feature of the structure drawn ALLOW the J will be the E isomer and I is the Z isomer ALLOW the J will be the trans isomer and I is the cis isomer ALLOW a description, eg the other isomer will have (carbon) chains diagonally arranged across the C=C or the other isomer will have hydrogen atoms diagonally arranged across the C=C bond DO NOT ALLOW draw trans but label as cis ALLOW energy required OR energy released ALLOW (energy change) when one mole of an element / compound / molecule / reactant DO NOT ALLOW one mole of reactants / product / substances / fuel / atoms ALLOW combusts in excess oxygen ALLOW burns in excess oxygen DO NOT ALLOW combust in excess air IGNORE fully oxidised IGNORE any conditions stated<br />
F322/01 Mark Scheme June 2013 Question Answer (e) (ii) FIRST, CHECK THE ANSWER ON ANSWER LINE IF answer = 7.06(42), award 2 marks. IF answer = 7.1, award 1 mark. q = 50.04.1833.8 OR 7064.2 (J) (cid:57) = 7.06(42) (kJ) (cid:57) (iii) FIRST, CHECK THE ANSWER ON ANSWER LINE IF answer = 0.005(00), award 2 marks. Mr = 268.0 (cid:57) amount used = 0.005(00) (mol) (cid:57) (iv) FIRST, CHECK THE ANSWER ON ANSWER LINE IF answer = -1413, award 3 marks. IF answer = 1413, award 2 marks. H = answer to (ii) answer to (iii) 7.0642 0.005 OR (cid:57) 1413 (cid:57) minus sign (this is an independent mark) (cid:57) Marks Guidance ALLOW 7.06 up to calculator value of 7.0642 correctly rounded DO NOT ALLOW ECF from marking point 1 IGNORE negative sign in answer IF there is an alternative answer, check to see if there is any ECF credit possible using working below ALLOW 268 ALLOW 5 x 103 ALLOW ECF from incorrect Mr IGNORE trailing zeros IF there is an alternative answer, check to see if there is any ECF credit possible using working below ALLOW ECF from (ii) and (iii) ALLOW 1410 up to calculator value of 1412.84 correctly rounded ALLOW answers in standard form 1.41 x 103 up to calculator value of 1.41284 x 103 correctly rounded Answer must be at least three significant figures ALLOW 1412 if answer to (ii) is 7.06 ALLOW 1420 if answer to (ii) is 7.1 14<br />
F322/01 Mark Scheme June 2013 Question (v) (e) (f) Marks Answer incomplete combustion OR not sufficient oxygen available AND carbon is formed (cid:57) C6H12O6 (cid:198) 2CO2 + 2C2H5OH (cid:57) use of yeast OR zymase (cid:57) anaerobic OR absence of oxygen OR any temperature between 20 and 45 oC OR water OR aqueous (cid:57) Total 19 15 Guidance IGNORE soot is formed, carbon monoxide is formed or carbon dioxide is formed ALLOW correct molecular OR structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) IGNORE state symbols Enzyme is not sufficient DO NOT ALLOW acid catalyst If there is a contradiction or an incorrect answer in any condition given then do not award this mark. ALLOW room temperature Temperature quoted must include unit ALLOW conditions shown in the equation IGNORE warm temperature IGNORE heat / warm Body temperature is not sufficient A limited supply of oxygen is not sufficient IGNORE low pressure OR atmospheric pressure DO NOT ALLOW high pressure OR a pressure above 2 atmospheres<br />

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