AQA Jun 2012 Paper 5 Q7

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section b do not write outside the box answer all questions in the spaces provided you may find the following electrode potential data helpful when answering this question electrode half equation cr o aq h aq e cr aq h o i o g h aq e h o i cr aq e cr aq zn aq e zn s cr aq e cr s e v a describe the colour changes that you would observe when an excess of zinc is added to an acidified solution of potassium dichromate vi in the absence of air for each colour change identify the coloured ions responsible and write an equation for each reaction that occurs with zinc in the equations you should represent the ions in their simplest form for example cr marks extra space wmp jun chem do not write outside the box b describe what you would observe when dilute aqueous sodium hydroxide is added dropwise until in excess to a dilute aqueous solution containing chromium iii ions write two equations to illustrate your observations in these equations you should give the full formula of each of the complexes for example cr h o marks extra space c when an aqueous solution containing cr h o ions is warmed in the presence of cl ions cr h o cl ions are formed and the colour of the solution changes name this type of reaction suggest in terms of electrons why the colours of the complex ions are different marks extra space question continues on the next page turn over wmp jun chem do not write outside the box d the chromium ii ion cr h o has different properties from the cr h o ion use data from the table on page to explain why in an open container cr h o aq ions change into cr h o aq ions suggest the identity of the products formed in each case when sodium carbonate solution is added to separate solutions containing cr h o aq ions and cr h o aq ions explain why the cr h o aq ions behave differently from the cr h o aq ions in your answer to this part of the question equations are not required marks extra space wmp jun chem

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