AQA Jun 2012 Paper 5 Q5

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do not write outside the box the table shows some electrode half equations and the associated standard electrode potentials equation number electrode half equation cd oh s e cd s oh aq zn aq e zn s nio oh s h o i e ni oh s oh aq mno s h o l e mno oh s oh aq o g h aq e h o i e v a in terms of electrons state the meaning of the term oxidising agent mark b deduce the identity of the weakest oxidising agent in the table explain how e values can be used to make this deduction weakest oxidising agent explanation marks c the diagram shows a non rechargeable cell that can be used to power electronic devices the relevant half equations for this cell are equations and in the table above cover carbon rod mno paste porous separator zinc zncl paste wmp jun chem do not write outside the box c i calculate the e m f of this cell mark c ii write an equation for the overall reaction that occurs when the cell discharges mark c iii deduce one essential property of the non reactive porous separator labelled in the diagram mark c iv suggest the function of the carbon rod in the cell mark c v the zinc electrode acts as a container for the cell and is protected from external damage suggest why a cell often leaks after being used for a long time mark question continues on the next page turn over wmp jun chem do not write outside the box d a rechargeable nickel cadmium cell is an alternative to the cell shown in part c the relevant half equations for this cell are equations and in the table on page d i deduce the oxidation state of the nickel in this cell after recharging is complete write an equation for the overall reaction that occurs when the cell is recharged oxidation state equation marks d ii state one environmental advantage of this rechargeable cell compared with the non rechargeable cell described in part c mark e an ethanol oxygen fuel cell may be an alternative to a hydrogen oxygen fuel cell when the cell operates all of the carbon atoms in the ethanol molecules are converted into carbon dioxide e i deduce the equation for the overall reaction that occurs in the ethanol oxygen fuel cell mark e ii deduce a half equation for the reaction at the ethanol electrode in this half equation ethanol reacts with water to form carbon dioxide and hydrogen ions mark e iii the e m f of an ethanol oxygen fuel cell is v use data from the table on page to calculate a value for the electrode potential of the ethanol electrode mark wmp jun chem e iv suggest why ethanol can be considered to be a carbon neutral fuel do not write outside the box marks turn over for the next question turn over wmp jun chem

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