OCR A Jun 2009 Paper 2 Q6 (with explained solutions) |

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OCR A Jun 2009 Paper 2 Q6

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6 A student carried out an investigation to compare the rates of hydrolysis of 1-iodopropane and 1-bromopropane. The student heated hot aqueous sodium hydroxide with each halogenoalkane and found that 1-iodopropane was hydrolysed faster. 12 The equation for the reaction with 1-iodopropane is shown below. CH3CH2CH2OH + I(a) (i) Outline the mechanism for this hydrolysis of 1-iodopropane. CH3CH2CH2I + OH Show curly arrows and relevant dipoles. [3] (ii) State the name of this type of mechanism.[1] (b) Explain why 1-iodopropane is hydrolysed faster than 1-bromopropane.[2] (c) Chlorofluoroalkanes, CFCs, were developed from fluoroalkanes and were used in aerosols and as refrigerants. Under the Montreal Protocol, CFCs are now largely banned because of their ozone-depleting properties. CFCs have now been replaced in many applications. Suggest two reasons why there is still concern about ozone depletion.[2]OCR 2009<br />
(d) Fluoroalkenes are used to make polymers. For example, PVF, (CH2CHF)n, is used to make non-flammable interiors of aircraft. (i) Draw two repeat units of the polymer PVF showing all bonds. 13 (ii) Draw the structure of the monomer of PVF. [1] [1] (e) Once polymers have been used, they become waste. Outline two ways that waste polymers are processed usefully, rather than just dumped in landfill sites.[2] [Total: 12]OCR 2009 Turn over<br />

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F322 Question 6 (i) (a) Mark Scheme June 2009 C2H5 (cid:71)(cid:14) C (cid:71)(cid:16) Expected Answers C2H5 OH I(cid:16) Marks OH(cid:16) CI curly arrow from the bond not from carbon atom (cid:57) curly arrow from the OH- (cid:57) correct partial charges on CI (cid:57) Additional Guidance no need to show any lone pairs on oxygen but must have a clear negative sign rather than partial negative charge IGNORE lone pairs IGNORE products of this reaction ALLOW curly arrow from a negative charge or from any part of hydroxide ion If SN1 mechanism is given then use the mark scheme below correct partial charges on CI (cid:57) CI curly arrow from the bond not from carbon atom (cid:57) curly arrow from the OH- to the correct carbocation (cid:57) C2H5 C2H5 H + C - OH (b) (ii) nucleophilic substitution (cid:57) CI bonds broken more easily (cid:57) CI bonds are weaker OR have less bond enthalpy OR CI bonds are longer (cid:57) 1 2 20 ALLOW ora e.g. CBr bonds are stronger OR broken less easily<br />
F322 Question (c) Any TWO from: Mark Scheme June 2009 Marks 12 Additional Guidance IGNORE because chlorine radicals stay in the stratosphere ALLOW other named ozone depleting substances e.g. NO and HFCs Free bonds at bond ends must be present ALLOW minor slip e.g. missing one hydrogen and left as a stick ALLOW more than two repeat units but must be a whole number of repeat units IGNORE brackets, use of numbers and n in the drawn structure ALLOW skeletal formula ALLOW CH2CHF IGNORE biodegradable used as a fuel is insufficient releases energy is insufficient ALLOW burning plastics to release energy ALLOW organic feedstock / raw materials to make organic compounds Expected Answers CFCs take many years to reach the ozone layer OR long residence time (cid:57) CFCs are still being used (cid:57) there are other ozone depleting substances (cid:57) (d) (i) (cid:57) (ii) (e) (cid:57) Any two from: separation into types and recycling OR sort plastics, melt and remould (cid:57) combustion for energy generation (cid:57) used for cracking OR feedstock for plastics or chemicals (cid:57) Total 21<br />

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