OCR A Jan 2011 Paper 2 Q1

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Answer all the questions. 1 Crude oil is a source of alkanes. (a) Fractional distillation is used to separate useful hydrocarbons found in crude oil. Explain, in terms of intermolecular forces, how fractional distillation works.[2] (b) The petroleum industry processes straight-chained alkanes into cycloalkanes such as cyclopentane and cyclohexane. CH2 H2C H2C CH2 CH2 H2C H2C CH2 CH2 CH2 CH2 cyclopentane cyclohexane (i) Deduce the general formula of a cycloalkane.[1] (ii) Construct the equation to show the formation of cyclohexane from hexane. (iii) Suggest why the petroleum industry processes hexane into cyclohexane.[1]OCR 2011 Turn over [1]<br />
 (c) The flowchart below shows some of the organic compounds that could be made starting from cyclohexane. Cl2 / UV Cl chlorocyclohexane compound A K2Cr2O7(aq) H2SO4(aq) KOH(aq) / warm H3PO4 / heat OH cyclohexanol cyclohexene HBr compound B Br2 Br Br (i) Explain why cyclohexene is described as unsaturated and as a hydrocarbon.[2] (ii) The reaction between chlorine and cyclohexane is an example of radical substitution. State one problem of using this reaction to prepare a sample of chlorocyclohexane.[1]OCR 2011<br />
 (iii) The formation of cyclohexanol from chlorocyclohexane involves the reaction of a nucleophile, the hydroxide ion. Suggest what feature of the hydroxide ion makes it able to act as a nucleophile.[1] (iv) Using the flowchart, draw the structures of compound A and compound B. compound A compound B [2] (v) Describe, using the curly arrow model, the mechanism for the reaction between Br2 and cyclohexene. Show relevant dipoles and charges. H2C CH2 H2C CH2 CC Br Br [4] [Total: 15]OCR 2011 Turn over<br />

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