AQA Jun 2014 Paper 5 Q7 (with explained solutions) |

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AQA Jun 2014 Paper 5 Q7

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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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question a i a ii h oh h o e h h e o e h o oh o h e h o hydrogen electrode produces electrons oxygen electrode accepts electrons mark scheme a level chemistry chem june marking guidance mark comments any order ignore reference to salt bridge do not allow at negative positive electrode must identify hydrogen and oxygen allow electrons flow to the oxygen electrode do not accept oxygen supplied as the only statement allow less energy wasted more efficient do not allow reference to safety of b hydrogen the fuel reactants supplied continuously fed in c in the fuel cell a greater proportion of the energy available from the hydrogen oxygen reaction is converted into useful energy d hydrogen is flammable h corrosive oh corrosive hydrogen explosive mark scheme a level chemistry chem june marking guidance mark comments in each of p and q the oxidation state of cr is both contain cr in each of p and q the electron configuration is the same d d ligands are different different energies of d electrons different split of d electron energy levels different energy gap of d electrons different d orbital energy different wavelengths frequencies energies of light colours of light are absorbed by the d electrons different wavelengths frequencies energies of light colours of light are transmitted reflected if oxidation states are different lose m and m do not allow just same number of electrons reference to emission and or uv light but not to visible loses m and m of question a mark scheme a level chemistry chem june co nh nh ch ch nh co nh ch ch nh nh particles form particles increase in number of particles disorder entropy increases s positive h is approx zero no net change in bond enthalpies g is negative g allow nh c h nh and ch nh ch nh allow partial substitution do not allow en or other formulae for m but can score m allow molecules entities ions moles instead of particles do not allow atoms can score m if numbers match candidates incorrect equation provided number of particles increases cannot score m if number of particles stated or in equation is the same or decreases allow same number and type of bonds broken and formed mark m and m independently of b c i bond angle o charge of zero c ii nh ptcl h o nh ptcl h o cl mark scheme a level chemistry chem june correct displayed structure must show all three n h bonds on each n ignore arrows and lone pairs attempt to show shape ignore charges on atoms in structure for m allow to degrees allow this angle for any complex with ligands eg if nh or cl used instead of nh award this mark if no charge shown on structure but if charges shown on ligands in m must state that overall charge allow m only if cisplatin is correct or if trans form or if nh not displayed or if nh used instead of nh if formula of cisplatin is incorrect mark consequentially provided h o replaces cl and charge on complex increases by one c iii use in small amounts short bursts target the application monitor the patients allow give patient time between doses of o v o vo v o so v o so v o so vo so v o acts as a catalyst lowers the activation energy speeds up the overall reaction between so and oxygen o v o d mark scheme a level chemistry chem june allow multiples of

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Topics to revise

AQA > Inorganic chemistry > Transition metals >

7 Formation of coloured ions

AQA > Organic Chemistry > Optical isomerism >

1 Optical isomerism

AQA > Organic Chemistry > Alkanes AS >

3 Combustion

AQA > Physical chemistry > Energetics and kinetics AS >

5 Kinetics

AQA > Inorganic chemistry > Transition metals >

6 Shape of complex ions

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