OCR A Jan 2013 Paper 2 Q1 (with explained solutions) |

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OCR A Jan 2013 Paper 2 Q1

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Answer all the questions. 1 Crude oil contains many hydrocarbons. The table shows information about some of these hydrocarbons. Hydrocarbon Molecular formula Boiling point / C Hexane 3-Methylpentane 2,2-Dimethylbutane C6H14 C6H14 C6H14 69 63 50 (a) What is the empirical formula of hexane?[1] (b) Explain why hexane is both saturated and a hydrocarbon. saturatedhydrocarbon[2] (c) Draw the skeletal formula for 2,2-dimethylbutane. [1] (d) Describe and explain the trend shown by the boiling points of the hydrocarbons in the table.[3]OCR 2013<br />
(e) Decane, C10H22, can be cracked to form hexane and one other product. Write an equation for this reaction.[1] (f) In the presence of ultraviolet radiation, butane, C4H10, reacts with chlorine to form a large number of organic products. Several of these products are structural isomers of C4H8Cl2. (i) Write an equation, using molecular formulae, for the formation of C4H8Cl2 from butane.[1] (ii) Complete the table below about two of the structural isomers of C4H8Cl2. Isomer 1 Isomer 2 Name 1,4-Dichlorobutane Displayed formulaCl Cl [2] (g) The reaction between butane and chlorine is an example of radical substitution. Initially, chlorobutane, C4H9Cl, is formed, which then reacts with more chlorine to form C4H8Cl2. (i) The first step of the reaction of C4H9Cl with chlorine is the homolytic fission of a chlorine molecule. What is meant by the term homolytic fission?[2] (ii) Complete the missing species in the propagation steps below. Cl + C4H9Cl++C4H8Cl2 +OCR 2013 [2] Turn over<br />
(h) Butane, C4H10, undergoes incomplete combustion when there is a shortage of oxygen. Write an equation for the incomplete combustion of butane.[1] [Total: 16]OCR 2013<br />

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F322/01 Mark Scheme January 2013 Question (a) C3H7 (cid:57) Answer Marks (b) (c) (d) (e) Saturated Only has (carbon to carbon) single bonds (cid:57) Hydrocarbon Contains (the elements) hydrogen and carbon only (cid:57) (cid:57) as branching increases the boiling point decreases OR the more branched the isomers of hexane are the lower the boiling point (cid:57) branched isomers have less surface (area) of contact OR branched fewer points of contact (than unbranched) (cid:57) (the more branched the) fewer van der Waals forces OR (the more branched) has weaker van der Waals forces OR Less energy required to break van der Waals forces (cid:57) C10H22 (cid:198) C6H14 + C4H8 OR C10H22 (cid:198) C6H14 + 2C2H4 (cid:57) Guidance ALLOW H7C3 ALLOW does not contain any (carbon to carbon) double bonds ALLOW all of the carbon atoms are bonded to four other atoms DO NOT ALLOW contains hydrogen and carbon DO NOT ALLOW a mixture of carbon and hydrogen only DO NOT ALLOW hydrogen and carbon molecules only ALLOW ORA throughout First marking point must compare boiling point and branching for all three isomers Reference to just surface area / closeness of molecules is not sufficient ALLOW vdw forces OR VDW forces (and any combination of upper and lower cases) DO NOT ALLOW VDW mark if answer states that these are between atoms or answer implies that these are bonds ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) IGNORE state symbols<br />
F322/01 Mark Scheme January 2013 Question Answer (f) (i) C4H10 + 2Cl2 (cid:198) C4H8Cl2 + 2HCl (cid:57) (ii) Isomer 1 Correct displayed formula eg: Isomer 2 1,3-dichlorobutane (cid:57) Cl Cl (cid:57) (g) (i) covalent bond breaking (cid:57) one electron (from the bond pair) goes to each atom OR makes (two) radicals (cid:57) (ii) Cl + C4H9Cl (cid:198) C4H8Cl + HCl (cid:57) C4H8Cl + Cl2 (cid:198) C4H8Cl2 + Cl (cid:57) C4H10 + 4O2 (cid:198) 4CO + 5H2O OR C4H10 + 2O2 (cid:198) 4C + 5H2O (cid:57) Marks Guidance IGNORE state symbols Must be a displayed formula ALLOW absence of hyphens 1 and 3 must be clearly separated: ALLOW full stops: 1.3 OR spaces: 1 3 DO NOT ALLOW 13 ALLOW covalent bond is split IGNORE particle for atom DO NOT ALLOW molecule or compound for atom DO NOT ALLOW to each molecule or to each reactant ALLOW one electron goes to each product / species IGNORE homolytic fission equations IGNORE dots even if incorrect ALLOW any correct multiples for these equations eg 2C4H10 + 9O2 (cid:198) 8CO + 10 H2O IGNORE state symbols ALLOW equations for incomplete combustion that give CO2 with CO and/or C eg C4H10 + 4O2 (cid:198) 3CO + C + 5H2O Total 16 (h)<br />

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