AQA Jan 2011 Paper 5 Q7

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do not write outside the box hydrogen peroxide is used as an oxidising agent in the preparation of transition metal complexes a consider the following reaction scheme all the complexes are in aqueous solution co h o cobalt ii complex reaction reaction co nh h o a i identify a reagent for reaction and describe the colour change that occurs marks a ii state the colour of the final solution formed in reaction mark wmp jan chem b consider the following reaction scheme all the complexes are in aqueous solution do not write outside the box cr h o chromium iii complex cro reaction h o reaction excess naoh aq b i for reaction state the colour of the initial and of the final solution and write an equation for the reaction marks b ii write a half equation for the reduction of hydrogen peroxide to hydroxide ions deduce an overall equation for reaction and state the colour of the final solution marks question continues on the next page turn over wmp jan chem do not write outside the box c the concentration of a hydrogen peroxide solution can be determined by titration with acidified potassium manganate vii solution in this reaction the hydrogen peroxide is oxidised to oxygen gas a cm sample of the hydrogen peroxide solution was added to a volumetric flask and made up to cm of aqueous solution a cm sample of this diluted solution was acidified and reacted completely with cm of mol dm potassium manganate vii solution write an equation for the reaction between acidified potassium manganate vii solution and hydrogen peroxide use this equation and the results given to calculate a value for the concentration in mol dm of the original hydrogen peroxide solution if you have been unable to write an equation for this reaction you may assume that mol of kmno react with mol of h o this is not the correct reacting ratio marks extra space end of questions wmp jan chem there are no questions printed on this page do not write on this page answer in the spaces provided wmp jan chem there are no questions printed on this page do not write on this page answer in the spaces provided copyright aqa and its licensors all rights reserved wmp jan chem

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