AQA Jun 2016 Paper 5 Q5 (with explained solutions) |

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AQA Jun 2016 Paper 5 Q5

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do not write outside the box a representation of a hydrogen oxygen fuel cell that operates in alkaline conditions is pt h h o o oh pt a i write a half equation for the reaction that occurs at each electrode use the half equations to deduce an overall equation for the cell marks half equation at positive electrode half equation at negative electrode overall equation a ii state and explain the effect if any of increasing the pressure of oxygen on the e m f of this cell marks effect on e m f explanation b complete the diagram to show how the e m f of a hydrogen oxygen fuel cell changes with time mark e m f time wmp jun chem do not write outside the box c i suggest the effect if any on the e m f of this cell if the surface area of each platinum electrode is increased mark c ii state the main environmental advantage of using a hydrogen oxygen fuel cell to power a car mark d suggest why the use of a hydrogen oxygen fuel cell might not be carbon neutral mark turn over for the next question turn over wmp jun chem

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mark scheme a level chemistry chem june comments allow multiples ignore state symbols if equations both correct but at the wrong electrodes allow mark mark independently must be this way round if decrease no change then ce if blank then mark on allow o h o e oh will move to the right oxygen half equation moves to the rhs e o oh half cell moves to the right must start at y axis time min unchanged ci of marking guidance mark m positive electrode o h o e oh m negative electrode h oh h o e h o h o aii increase emf h o h o will move to the right or overall equation moves to the right b e m f v question ai mark scheme a level chemistry chem june not fuel cell does not give out pollutants unless pollutant stated allow co is released to produce the hydrogen water is the only product fuel cell does not give out pollutants such as nox or co or so or c or co or cxhy or unburnt hydrocarbons co is released because fossil fuels are burned to produce electricity to generate hydrogen or co is released when methane reacts with steam to produce hydrogen of cii d mark scheme a level chemistry chem june marking guidance mark comments h h products h reactants or kj mol s s products s reactants jk mol causes an increase in order a decrease in disorder penalise incorrect units ignore missing units allow kj k mol units must be given and must match value allow products more ordered products less disordered if answer to b is ve allow products are less ordered causes an increase in disorder causes a decrease in order of question a b c

Question 1 2 3 4 5 6 7 8 9

Topics to revise

AQA > Organic Chemistry > Alkanes AS >

3 Combustion

AQA > Physical chemistry > Energetics and kinetics AS >

5 Kinetics

AQA > Physical chemistry > Thermodynamics >

5 Gibb’s Free Energy

AQA > Physical chemistry > Equilibrium AS >

1 Dynamic equilibrium and factors affecting equilibrium

AQA > Physical chemistry > Atomic structure AS >

4 Electronic arrangement

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