7 Formation of coloured ions

 

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Oxford Textbook Pages : 364 - 366

CGP Revision Guide Pages : 114 - 115

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Show Specification Ref : 3.2.5.4

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Question 1 / 5

AQA Jan 2011 Paper 5 Q7 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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Question 2 / 5

AQA Jun 2011 Paper 5 Q7 section b answer all questions in the spaces provided do not write outside the box this question is about copper chemistry a aqueous copper ii ions cu h o aq are blue a i with reference to electrons explain why aqueous copper ii ions are blue marks extra space a ii by reference to aqueous copper ii ions state the meaning of each of the three terms in the equation e hv marks extra space wmp jun chem do not write outside the box a iii write an equation for the reaction in aqueous solution between cu h o and an excess of chloride ions state the shape of the complex produced and explain why the shape differs from that of the cu h o ion marks extra space b draw the structure of the ethanedioate ion c o explain how this ion is able to act as a ligand marks question continues on the next page turn over wmp jun chem do not write outside the box c when a dilute aqueous solution containing ethanedioate ions is added to a solution containing aqueous copper ii ions a substitution reaction occurs in this reaction four water molecules are replaced and a new complex is formed c i write an ionic equation for the reaction give the co ordination number of the complex formed and name its shape marks c ii in the complex formed the two water molecules are opposite each other draw a diagram to show how the ethanedioate ions are bonded to a copper ion and give a value for one of the o cu o bond angles you are not required to show the water molecules marks wmp jun chem
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Question 3 / 5

AQA Jun 2012 Paper 5 Q7 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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Question 4 / 5

AQA Jun 2013 Paper 5 Q6 do not write outside the box this diagram represents the energy change that occurs when a d electron in a transition metal ion is excited by visible light e excited state ground state a give the equation that relates the energy change e to the planck constant h and the frequency of the visible light v use this equation and the information in the diagram to calculate a value for the frequency of the visible light and state the units the planck constant h j s equation calculation marks b explain why this electron transition causes a solution containing the transition metal ion to be coloured marks wmp jun chem do not write outside the box c the energy change shown in the diagram represents the energy of red light and leads to a solution that appears blue blue light has a higher frequency than red light suggest whether the energy change e will be bigger smaller or the same for a transition metal ion that forms a red solution explain your answer energy change explanation marks d state three different features of transition metal complexes that cause a change in the value of e the energy change between the ground state and the excited state of the d electrons feature feature feature marks turn over for the next question turn over wmp jun chem
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AQA Jun 2014 Paper 5 Q7 section b answer all questions in the spaces provided do not write outside the box the characteristic properties of transition metals include coloured ions complex formation and catalytic activity a consider the chromium complexes p and q cr h o aq red violet cr h o cl aq green explain with reference to oxidation states and electron configurations why the chromium ions in complexes p and q contain the same number of d electrons you should not consider the electrons donated by the ligands explain in terms of electrons why the complexes are different colours you are not required to explain why the observed colours are red violet and green marks wmp jun chem do not write outside the box b write an equation to show how the co nh aq ion reacts with diaminoethane explain the thermodynamic reasons why this reaction occurs marks question continues on the next page turn over wmp jun chem do not write outside the box c the toxic complex cisplatin is an effective anti cancer drug because it reacts with the dna in cancer cells preventing cell division c i draw the displayed structure of cisplatin on your structure show the value of one of the bond angles at platinum state the charge if any on the complex marks c ii when cisplatin is ingested an initial reaction involves one of the chloride ligands being replaced by water write an equation for this reaction mark c iii suggest how the risk associated with the use of this drug can be minimised mark wmp jun chem do not write outside the box d explain with the aid of equations how and why vanadium v oxide is used in the contact process marks turn over for the next question turn over wmp jun chem
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