AQA AS Jun 2016 Paper 2 Q5

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12Refrigerants are substances used to cool refrigerators and freezers. Until recently, many of the compounds used as refrigerants were chlorofluorocarbons (CFCs), but these are now known to form chlorine radicals. CFCs have been phased out in many countries by international agreement. 0 5 the upper atmosphere. . 1 Write two equations to show how chlorine radicals react with ozone molecules in [2 marks] 0 5 . 2 Chloropentafluoroethane is a CFC that has been used as a refrigerant. Draw its displayed formula. [1 mark] . 3 1,1,1-trifluoroethane (CF3CH3) is one of the molecules that has been used as a refrigerant in place of CFCs. Explain why 1,1,1-trifluoroethane does not lead to the depletion of the ozone in the upper atmosphere. [1 mark] 0 5 *12* M/JUN16/7404/2<br /> 130 5 . 4 One of the steps in the synthesis of 1,1,1-trifluoroethane (CF3CH3) is the reaction of 1,1-difluoroethane (CHF2CH3) with fluorine in a free-radical substitution reaction. Write two equations to represent the propagation steps in this conversion of CHF2CH3 into CF3CH3 [2 marks] Propagation step 1 Propagation step 2 0 5 . 5 A refrigerator contains 1.41 kg of 1,1,1-trifluoroethane (CF3CH3). Calculate the number of molecules of 1,1,1-trifluoroethane in the refrigerator. Give your answer to an appropriate number of significant figures. (The Avogadro constant L = 6.022 x 1023 mol1) [2 marks] 0 5 . 6 There are growing concerns about the use of 1,1,1-trifluoroethane as a refrigerant as it is a greenhouse gas that absorbs some of Earths infrared radiation. Give one reason why bonds in molecules such as carbon dioxide and 1,1,1-trifluoroethane absorb infrared radiation. [1 mark] *13* Turn overM/JUN16/7404/2<br />

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