AQA Jun 2010 Paper 5 Q7

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do not write outside the box the electrons transferred in redox reactions can be used by electrochemical cells to provide energy some electrode half equations and their standard electrode potentials are shown in the table below half equation cr o aq h aq e cr aq h o l fe aq e fe aq h aq e h g fe aq e fe s li aq e li s e v a describe a standard hydrogen electrode marks wmp jun chem do not write outside the box b a conventional representation of a lithium cell is given below this cell has an e m f of v li s li aq li aq mno s limno s pt s write a half equation for the reaction that occurs at the positive electrode of this cell calculate the standard electrode potential of this positive electrode marks c suggest what reactions occur if any when hydrogen gas is bubbled into a solution containing a mixture of iron ii and iron iii ions explain your answer marks question continues on the next page turn over wmp jun chem do not write outside the box d a solution of iron ii sulfate was prepared by dissolving g of feso h o mr in water and making up to cm of solution the solution was left to stand exposed to air and some of the iron ii ions became oxidised to iron iii ions a cm sample of the partially oxidised solution required cm of mol dm potassium dichromate vi solution for complete reaction in the presence of an excess of dilute sulfuric acid calculate the percentage of iron ii ions that had been oxidised by the air marks extra space copyright aqa and its licensors all rights reserved end of questions wmp jun chem

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