Edexcel Jun 2012 Paper 5 Q12 (with explained solutions) |

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Edexcel Jun 2012 Paper 5 Q12

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SECTION B Answer ALL the questions. Write your answers in the spaces provided. 12 This question is about benzene and its compounds. (a) A Kekul structure of benzene suggests the molecule consists of alternate double and single carbon to carbon bonds. The standard enthalpy change of hydrogenation of a carbon to carbon double bond is 120 kJ mol1. (i) Calculate the standard enthalpy change of hydrogenation of benzene for the Kekul structure. (1)*(ii) The actual standard enthalpy change of hydrogenation of benzene is 208 kJ mol1. Use this information and your answer to (i), to calculate the difference in stability of benzene and the Kekul structure. What does this tell us about the bonding in benzene? Explain how this influences the type of chemical reactions that benzene undergoes. (4)*P39309A0920* Turn over<br />
(b) The flow chart shows some typical reactions of benzene. C6H5NO2 nitrobenzene benzene bromobenzene C6H5Br C6H6 Br2/FeBr3 fuming sulfuric acid Compound A (i) Identify the two chemicals needed to make nitrobenzene from benzene. (2)(ii) Classify the type of reagent required in all three reactions. (1)(iii) Show, with appropriate diagrams, the mechanism for the reaction of benzene with bromine, in the presence of iron(III) bromide, to form bromobenzene. Include the formation of the ion attacking the benzene molecule. (4) 10 *P39309A01020*<br />
(iv) Give the structural formula and the name for compound A. (2) Name(c) (i) Explain why phenol, C6H5OH, and methoxybenzene, C6H5OCH3, are much more reactive than benzene with bromine. (3)(ii) Write the equation for the reaction between phenol and bromine water. State symbols are not required. (d) Diphenylmethane, (C6H5)2CH2, is often added to soap to create the pleasant smell of geraniums. It can be made from benzene and one other reagent, using a suitable catalyst. Identify the other starting material and the catalyst by name or formula. (2) (2)(Total for Question 12 = 21 marks) *P39309A01120* 11 Turn over<br />

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Mark Mark Acceptable Answers Reject No sign or + sign in answer, ie 360/+360 Any other wrong units E Reject Attack by electrophiles with no mention of substitution (3 x -120) = -360 (kJ mol-1) IGNORE H, and case of letters in units e.g allow Kj Acceptable Answers( Bonding in) benzene/it is more stable (than Kekule) by 152 kJ mol-1 (consequential on (a)(i)) (1) IGNORE sign/p/double bond electrons are delocalized (around the ring) OR six p electrons shared between six (ring) carbon atoms OR delocalized because of overlap of p orbitals OR resonance hybrid of C=Cs and C-Cs (1)Substitution reactions (rather than addition) (1) NOTE: Nucleophilic substitution negates the substitution mark because it is wrong additional informationMaintains/regains delocalized system OR maintains/regains stability OR maintains/regains stabilization energy (1) Section B Question Number 12(a)(i) Question Number *12(a)(ii)<br />
Question Number 12(b)(i) Concentrated nitric acid/HNO3 (1) Acceptable Answers Mark Reject Concentrated hydrochloric acid Mark Reject Acid Base Oxidizing agent Reducing agent Concentrated sulfuric acid/H2SO4 (1) Allow conc or c. in place of concentrated ALLOW Concentrated nitric acid and sulfuric acid OR Concentrated HNO3 and H2SO4 (2) Second mark depends on nitric acid Max. (1) if no mention of concentrated Nitric acid and concentrated sulfuric acid scores (1) NOTE: conc. HNO3 and H2SO4(aq) scores (1) but conc. HNO3 and conc H2SO4(aq) scores (2) Question Number 12(b)(ii) Electrophile/electrophilic Acceptable Answers ALLOW Electrophyl(e)<br />
Reject Mark lack of charges Question Number 12(b)(iii) Br2 + FeBr3FeBr4 Acceptable Answers - + Br+ OR Br-Br + FeBr3Br +Br -FeBr3 (1) IGNORE state symbols even if wrong Br+/Br+(BrFeBr3) Br (+ FeBr3) Br + H+ /HBr (+ FeBr3) Arrow from benzene ring electrons (from inside the hexagon) to Br+/Br+(Br-FeBr3) (1) Correctly drawn intermediate with delocalization covering at least three carbon atoms, but not the carbon atom bonded to the bromine with the positive charge shown inside the hexagon The bonds to H and Br may be dotted (1) Arrow from or close to bond to H to centre of ring and H+/HBr as a product (1) ALLOW Kekul structure for benzene and intermediate Each marking point is independent<br />
Question Number 12(b)(iv) Acceptable Answers Reject Mark Mark Benzenesulfuric acid/benzosulfonic acid/benzylsufonic acid Reject from methyl/methoxy Makes it more electronegative SO3H OR C6H5SO3H -H+ accept: displayed -SO3H -SO3 -SO2OH If two formulae are given both must be correct (1) Penalise if bond clearly goes to O or H rather than S Benzenesulfonic acid (1) ALLOW phenyl sulfonic acid Question Number 12(c)(i) Non-bonding/lone pair electrons from Acceptable Answers oxygen (1) are delocalized/incorporated/donated into the ring (electron system) (Could be shown in diagram) OR increases electron density on the ring (1) makes it (the ring) more susceptible to electrophilic attack/makes it (the ring) a better nucleophile (1)<br />
Question Number 12(c)(ii) Acceptable Answers OH + 3Br2 Br OH Br Reject Mark Br + 3HBr (1) balancing ALLOW (1) organic formulaCondensed structural formulae, for example C6H5OH + 3Br2C6H2Br3OH +3HBr (1) (1) balancing multiplessubstitution to any positions IGNORE: H2O Position of bond to OH NOTE: Correct balanced equations giving mono and disubstitution phenols score 1 mark<br />
Acceptable Answers Reject Mark (Chloromethyl)benzene/chloromethylbenzene/ chlorophenylmethane/ benzyl chloride OR dichloromethane (1) ALLOW phenylchloromethane Aluminium chloride (1) ACCEPT formulae eg C7H7Cl, C6H5CH2Cl, CH2Cl2, AlCl3 ACCEPT other halogen carriers eg FeCl3/iron(III) chloride/ZnCl2 ACCEPT bromine in place of chlorine for either/both marks Correct formula and wrong name or correct name and wrong formula or any other wrong additional information loses mark CH2Cl Question Number 12(d)<br />

Question 12 13 14 15

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