AQA Jun 2012 Paper 2 Q6 (with explained solutions) |

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AQA Jun 2012 Paper 2 Q6

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do not write outside the box chloromethanes such as dichloromethane and trichloromethane are produced in industry as they have many uses trichloromethane has been used in the manufacture of the refrigerant chlorodifluoromethane a chlorine can react with dichloromethane ch cl to form trichloromethane chcl a i write an equation for each of the following steps in the mechanism for this reaction initiation step first propagation step second propagation step marks a ii give one essential condition for this reaction and name the type of mechanism essential condition type of mechanism marks question continues on the next page turn over wmp jun chem do not write outside the box b an organic product x with mr is obtained when chlorine reacts with trichloromethane b i write an equation for the overall reaction of chlorine with trichloromethane to form x by the same mechanism as that outlined in part a i mark b ii the following infrared spectrum was obtained for a sample of x produced in this reaction transmittance wavenumber cm use this infrared spectrum to explain why it is possible to deduce that this sample of x contains no trichloromethane you may find it helpful to refer to table on the data sheet marks extra space wmp jun chem do not write outside the box c explain with the aid of equations and the intermediates that form in the ozone layer why the european union has banned the use of chlorodifluoromethane chclf as a refrigerant marks extra space d the compound tetrafluoropropene is the refrigerant used in all new car air conditioners d i draw the displayed formula for tetrafluoropropene d ii give one reason why tetrafluoropropene is a more environmentally acceptable refrigerant than chlorodifluoromethane mark mark turn over wmp jun chem

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mark scheme general certificate of education a level chemistry unit chemistry in action june mark comments penalise absence of dot once only penalise or charges every time accept dot anywhere on chcl radical but if the structure is drawn out the dot must be on the carbon atom penalise this error once only penalise once only for a line and two dots to show a bond penalise once only for double headed curly arrows mark independently allow x as alternative to ccl only if x is clearly identified as ccl question a i marking guidance initiation m cl cl m first propagation cl ch cl chcl hcl m second propagation cl chcl chcl cl a ii m condition ultra violet uv sun light or high temperature or oc t oc m type of mechanism free radical substitution mechanism b i chcl cl ccl hcl mark scheme general certificate of education a level chemistry unit chemistry in action june b ii m trichloromethane chcl has a c h bond or x ccl it has no c h bond m the infrared spectrum shows absorption peak for c h in range to cm is missing m must refer to presence or absence of the c h bond in a compound m answer must refer to imply the spectrum allow the words dip or spike or low transmittance as alternatives for absorption ignore references to other absorptions c mark scheme general certificate of education a level chemistry unit chemistry in action june penalise m if cl is formed from cl as the only reaction or an additional reaction do not penalise an incorrect equation using chclf if correct reference is made to cl formation or c cl carbon chlorine bond breakage m and m either order penalise absence of dot once only accept dot anywhere on clo radical award m for the general idea behind the eu justification for banning the use of cfcs as refrigerants penalise m if overall ozone decomposition equation is incorrect ignore greenhouse effect global warming etc or cl chlorine free radical forms or correct equation chclf cl chf m a statement about bond breakage formation of cl c cl carbon chlorine bond breakage occurs m cl o clo o m clo o cl o m chclf chlorine containing compounds cfcs damage react with decrease the ozone layer or this overall decomposition occurs o o or without an ozone layer or with a decreased ozone layer uv radiation is not being filtered prevented from passing through the atmosphere or there is a concern about an increase in skin cancer etc or cl catalyses the decomposition of ozone a single cl causes chain reaction decomposition of many ozone molecules ozone layer mark scheme general certificate of education a level chemistry unit chemistry in action june all bonds must be drawn out ignore chlorine molecules tetrafluoropropene it does not contain chlorine atoms c cl bonds or it does not produce cl does not produce chlorine free radical s or chlorodifluoromethane does contain chlorine does produce cl does produce chlorine free radical s or c f is too strong and does not break create radicals or c f is stronger than c cl d i d ii

Question 1 2 3 4 5 6 7 8 9

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