OCR A Jan 2012 Paper 2 Q1 (with explained solutions) |

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OCR A Jan 2012 Paper 2 Q1

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Answer all the questions. 1 Crude oil is a source of many hydrocarbons. The skeletal formulae of some of these hydrocarbons are shown below. (a) Explain why compound A is both saturated and a hydrocarbon.[2] (b) What is the empirical formula for compound A?[1] (c) Give the letters, A, B, C, D, E, F, G, H or I, of two hydrocarbons that are structural isomers of each other.and[1]OCR 2012<br />
(d) The petroleum industry processes straight chain alkanes into cyclic hydrocarbons such as A, B and E. (i) Explain why the petroleum industry processes straight chain alkanes into cyclic hydrocarbons.[1] (ii) Hydrocarbon C can be processed into the cyclic hydrocarbon B. Construct an equation for this reaction. [1] (e) Explain why hydrocarbon D has a higher boiling point than hydrocarbon C.[2] (f) Hydrocarbons G and H are stereoisomers of each other. Explain what is meant by the term stereoisomerism.[2] (g) Construct the equation for the complete combustion of hydrocarbon C.[2]OCR 2012 Turn over<br />
(h) A hydrocarbon molecule, C16H34, is cracked to form an octane molecule and two molecules of but-2-ene. Construct the equation for this reaction.[1] (i) Compound I is 3-methylheptane. It does not contain a functional group. (i) What is meant by the term functional group?[1] (ii) Compound I reacts with chlorine in the presence of ultraviolet radiation to give several structural isomers of C8H17Cl. How many structural isomers could be formed in this reaction?[1] (iii) The mechanism of the reaction involves radicals. What is meant by the term radical ?[1] [Total: 16]OCR 2012<br />

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F322 Question 1 (a) Answer (a compound) with no double bond (or triple bond) (cid:57) containing hydrogen and carbon only (cid:57) Marks (b) (c) CH2 (cid:57) D and I OR F and G OR F and H (cid:57) (d) (i) Cyclic hydrocarbons have more efficient combustion (cid:57) Mark Scheme January 2012 Guidance ALLOW contains single bonds only ALLOW it contains just carbon and hydrogen DO NOT ALLOW a mixture of carbon and hydrogen OR only carbon and hydrogen molecules ALLOW H2C DO NOT ALLOW G and H The answer must relate to combustion or burning Assume they refers to the cyclic hydrocarbons ALLOW cyclic hydrocarbons allow smoother burning OR cyclic hydrocarbons increase octane number OR cyclic hydrocarbons reduce knocking OR cyclic hydrocarbons are less likely to produce pre-ignition OR cyclic hydrocarbons are more efficient fuels OR cyclic hydrocarbons burn better OR easier to burn OR cyclic hydrocarbon combust more easily OR improves combustion DO NOT ALLOW cyclic hydrocarbons ignite more easily ALLOW ora for straight chain hydrocarbons IGNORE cyclic hydrocarbons increase volatility of fuel IGNORE cyclic hydrocarbons have a lower boiling point cyclic hydrocarbons are a better fuel on their own is NOT sufficient cyclic hydrocarbons burn more cleanly on their own is NOT sufficient<br />
F322 Question 1 (d) (ii) C7H16 (cid:198) C7H14 + H2 (cid:57) Answer Mark Scheme Marks (e) D has more surface (area of) contact OR D is a bigger molecule (cid:57) D has more van der Waals forces OR C have fewer van der Waals forces (cid:57) (f) Same structural formula (cid:57) Different arrangement of groups around a double bond OR different arrangement (of atoms) in space (cid:57) January 2012 Guidance ALLOW molecular formulae OR correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) DO NOT ALLOW cycloheptane structure in equation Both answers need to be comparisons Assume it refers to D ALLOW has more electrons OR longer (carbon) chain OR higher molecular mass IGNORE surface area ALLOW ORA ALLOW D has stronger van der Waals forces / larger VDW / greater VDW OR C has weaker van der Waals forces OR C has smaller VDW ALLOW more VDW forces More intermolecular forces is not sufficient DO NOT ALLOW reference to bonds breaking or more bonds present unless it is clear that that the bonds are VDW ALLOW have the same structure / displayed formula / skeletal formula Stereoisomers have the same formula or molecular formula is not sufficient ALLOW different three dimensional arrangement<br />
F322 Question 1 (g) Answer C7H16 + 11O2 (cid:198) 7CO2 + 8H2O Correct reactants and products (cid:57) Balancing (cid:57) Mark Scheme Marks (h) C16H34 (cid:198) C8H18 + 2C4H8 (cid:57) (i) (i) Group of atoms (in a molecule or compound) that is responsible for the reactions (cid:57) (ii) 8 (cid:57) (iii) has an unpaired electron (cid:57) Total 16 January 2012 Guidance ALLOW molecular formulae OR correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) ALLOW any correct multiple IGNORE state symbols Balancing is dependent on correct formulae ALLOW molecular formulae OR correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) ALLOW any correct multiple ALLOW structural OR displayed OR skeletal formulae in equation ALLOW but-1-ene IGNORE state symbols ALLOW the 'part' (of the molecule or compound) that reacts ALLOW the group of atoms that gives the chemical properties ALLOW group of atoms which indicates the homologous series ALLOW plural i.e. unpaired electrons has a lone OR single OR free electron is not sufficient<br />

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