OCR A Jan 2010 Paper 2 Q1 (with explained solutions) |

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OCR A Jan 2010 Paper 2 Q1

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Answer all the questions. 1 Kerosene is used as a fuel for aeroplane engines. (a) Kerosene is obtained from crude oil. Name the process used to obtain kerosene from crude oil and explain why the process works.[2] (b) Some of the hydrocarbons in kerosene have the formula C10H22. (i) What is the name of the straight chain hydrocarbon with the formula C10H22?[1] (ii) Draw the skeletal formula of one branched chain isomer with the formula C10H22. [1] (iii) Explain why the straight chain isomer of C10H22 has a higher boiling point than any of its branched chain structural isomers.[2] (iv) Explain why the straight chain isomer of C10H22 is converted by the petroleum industry into its branched chain isomers.[1]OCR 2010<br />
(c) When kerosene burns in an aeroplane engine very little carbon monoxide, CO, is formed but a significant amount of nitrogen monoxide, NO, is formed. (i) Construct the equation to show the complete combustion of C10H22.[2] (ii) Suggest, with the aid of an equation, how NO is formed within an aeroplane engine.[1] (d) NO is a radical and contributes towards ozone depletion in the stratosphere. (i) What is a radical ?[1] (ii) One of the processes leading to the breakdown of ozone in the stratosphere can be represented by the following two equations. NO(g) + O3(g) NO2(g) + O2(g) NO2(g) + O(g) NO(g) + O2(g) What is the role of the NO in this process?[1] (iii) Ozone in the stratosphere is broken down to make O2 and O. Describe and explain how the concentration of ozone in the stratosphere is maintained.[2] (iv) Why is it important to life on the Earths surface that the concentration of ozone in the stratosphere is maintained?[1]OCR 2010 [Total: 15] Turn over<br />

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$F322 F322 Chains, Energy and Resources Mark Scheme January 2010 Question (a) Expected Answers Fractional distillation (cid:57) Because fractions have different boiling points (cid:57) Marks (b) (i) Decane (cid:57) Skeletal formula of branched C10H22 (cid:57) (ii) Additional Guidance DO NOT ALLOW just distillation For fractions, ALLOW components OR hydrocarbons OR compounds ALLOW condense at different temperatures ALLOW because van der Waals forces differ between molecules IGNORE reference to melting points IGNORE crude oil OR mixture has different boiling pointsbut ALLOW separates crude oil by boiling points DO NOT ALLOW deceane Formula must be skeletal AND must not include any symbol, e.g. CH3 Any possible skeletal formulae e.g. 13<br /> F322 Question Expected Answers Mark Scheme Marks Additional Guidance January 2010 (iii) Decane has more surface contact OR branched chains have less surface contact (cid:57) Decane has more van der Waals forces OR branched chains have fewer van der Waals forces (cid:57) (iv) Branched chains have more efficient combustion OR decane has less efficient combustion (cid:57) 14 Both answers need to be comparisons Assume it refers to decane IGNORE surface area ALLOW straight chains can get closer together OR branched chains cannot get as close to one another IGNORE branched chain are more compact ALLOW Decane has stronger van der Waals forces OR branched chains have weaker van der Waals forces More intermolecular forces is not sufficient ALLOW branched chains are easier to burn OR easier to combust OR burn better OR more efficient fuel OR less likely to produce pre-ignition or knocking OR increases octane rating ALLOW ORA for decane<br /> F322 Question Expected Answers Mark Scheme Marks (c) (i) C10H22 + 15O2 (cid:127)(cid:111) 10CO2 + 11H2O All four species correct (cid:57) balancing of four correct species (cid:57) (ii) N2 + O2 (cid:127)(cid:111) 2NO (cid:57) January 2010 Additional Guidance Better fuel is NOT sufficient Burns more cleanly is NOT sufficient ALLOW any correct multiple IGNORE state symbols ALLOW any correct multiple including fractions IGNORE state symbols The mark is for the equation IGNORE writing 15<br /> F322 Question (d) (i) Species with an unpaired electron (cid:57) Expected Answers Mark Scheme Marks (ii) catalyst (cid:57) (iii) O + O2 (cid:127)(cid:111) O3 OR O reacts with O2 to make ozone OR the reaction is reversible (cid:57) Rate of formation of ozone is the same as rate of decomposition (cid:57) (iv) absorbs (harmful) UV (cid:57) Total 15 16 January 2010 Additional Guidance ALLOW atom, molecule or particle with an unpaired electron ALLOW has an unpaired electron ALLOW particle formed by homolytic fission DO NOT ALLOW particle with a single electron OR particle with a free electron ALLOW O2 + OO3 OR O3O2 + O (cid:57)(cid:57) ALLOW is in equilibrium ORin correct equation OR has steady state condition (cid:57) IGNORE other equations involving ozone ALLOW keeps out UV OR filters UV ALLOW increased UV could cause skin cancer OR increased UV could cause cataracts OR increased UV could cause mutation of crops (cid:57) IGNORE gamma<br />$

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