2 CFCs and the ozone layer

 

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Oxford Textbook Pages : 235 - 237

CGP Revision Guide Pages : 106 - 107

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Show Specification Ref : 4.2.2e

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Question 1 / 5

AQA Jan 2011 Paper 2 Q1 section a answer all questions in the spaces provided do not write outside the box oxygen and ozone o both occur as gases in the upper atmosphere chlorine atoms catalyse the decomposition of ozone and contribute to the formation of a hole in the ozone layer these chlorine atoms are formed from chlorofluorocarbons cfcs such as cf cl a i give the iupac name of cf cl mark a ii complete the following equation that shows the formation of a chlorine atom from a molecule of cf cl cl cl cid mark a iii state what the cid represents in cl cid mark b write two equations that show how chlorine atoms catalyse the decomposition of ozone into oxygen equation equation marks wmp jan chem do not write outside the box c an equilibrium is established between oxygen and ozone molecules as shown below o g o g h kj mol c i state le chatelier s principle mark extra space c ii use le chatelier s principle to explain how an increase in temperature causes an increase in the equilibrium yield of ozone marks extra space d chemists supported the legislation to ban the use of cfcs modern refrigerators use pentane rather than cfcs as refrigerants with reference to its formula state why pentane is a more environmentally acceptable refrigerant mark extra space turn over wmp jan chem
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Question 2 / 5

AQA Jun 2011 Paper 2 Q7 do not write outside the box a halogens are used to make halogenated organic compounds the refrigerant used in air conditioners is a mixture of fluorinated alkanes these compounds are made by fluorination reactions the mechanism for the reaction of fluorine with an alkane or with a fluoroalkane is a free radical substitution similar to the reaction of chlorine with methane a i write the overall equation for the reaction of fluorine with methane to form trifluoromethane chf mark a ii write equations for the following steps in the mechanism for the reaction of fluorine with trifluoromethane chf to form tetrafluoromethane cf initiation step first propagation step second propagation step a termination step leading to the formation of hexafluoroethane marks wmp jun chem do not write outside the box b chlorofluorocarbons cfcs were used as refrigerants in the upper atmosphere ultra violet radiation breaks bonds in the cfcs to produce a reactive intermediate that catalyses the decomposition of ozone b i an example of a cfc is trichloro difluoroethane draw the displayed formula of this cfc mark b ii identify a bond in a cfc that is broken by ultra violet radiation to produce a reactive intermediate give the name of this reactive intermediate that catalyses the decomposition of ozone write an overall equation for this decomposition of ozone bond broken name of the reactive intermediate overall equation marks turn over for the next question turn over wmp jun chem
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Question 3 / 5

AQA Jun 2012 Paper 2 Q6 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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Question 4 / 5

AQA Jun 2015 Paper 2 Q5 do not write outside the box a there are many uses of halogenated organic compounds despite environmental concerns bromotrifluoromethane is used in fire extinguishers in aircraft bromotrifluoromethane is formed when trifluoromethane reacts with bromine chf br cbrf hbr the reaction is a free radical substitution reaction similar to the reaction of methane with chlorine a i write an equation for each of the following steps in the mechanism for the reaction of chf with br initiation step marks first propagation step second propagation step a termination step a ii state one condition necessary for the initiation of this reaction mark wmp jun chem do not write outside the box b bromine containing and chlorine containing organic compounds may have a role in the decomposition of ozone in the upper atmosphere b i draw an appropriate displayed formula in the space provided to complete the following equation to show how cbrf may produce bromine atoms in the upper atmosphere mark cbrf br b ii in the upper atmosphere it is more likely for cbrf to produce bromine atoms than it is for cclf to produce chlorine atoms suggest one reason for this mark question continues on the next page turn over wmp jun chem do not write outside the box b iii bromine atoms have a similar role to chlorine atoms in the decomposition of ozone the overall equation for the decomposition of ozone is o o write two equations to show how bromine atoms br act as a catalyst in the decomposition of ozone explain how these two decomposition equations show that bromine atoms behave as a catalyst marks equation equation explanation wmp jun chem
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Question 5 / 5

AQA Jun 2016 Paper 2 Q3 do not write outside the box a haloalkanes are used as refrigerants solvents and anaesthetics trichloromethane chcl is a haloalkane that can be formed by heating a mixture of chloromethane ch cl and chlorine a i write an overall equation for the formation of trichloromethane by the reaction of chloromethane with chlorine mark a ii name the mechanism for this formation of trichloromethane mark a iii dichloromethane ch cl is an intermediate in this formation of trichloromethane write an equation for each of the following steps in the mechanism for the reaction of dichloromethane with chlorine marks initiation step first propagation step second propagation step a termination step leading to the formation of a compound with formula c h cl wmp jun chem do not write outside the box b chlorotrifluoromethane cclf is used as a refrigerant but is being phased out due to concerns about ozone depletion in the upper atmosphere in the upper atmosphere cclf decomposes in the presence of uv light forming a reactive intermediate that catalyses the decomposition of ozone b i write an equation to show how cclf decomposes to form the reactive intermediate mark b ii write two equations to show how this reactive intermediate is involved in catalysing the decomposition of ozone marks turn over for the next question turn over wmp jun chem
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