Q1.Which one of the following reactions in aqueous solution has the most positive change in entropy?
A       [Cu(H2O)6]2+ + 4NH3 → [Cu(NH3)4(H2O)2]2+ + 4H2O
B       [Cu(H2O)6]2+ + 4Cl− → [CuCl4]2− + 6H2O
C       [Cu(H2O)6]2+ + EDTA4− → [Cu(EDTA)]2− + 6H2O
D       [Cu(H2O)6]2+ + 2H2NCH2CH2NH2 → [Cu(H2NCH2CH2NH2)2(H2O)2]2+ + 4H2O
(Total 1 mark)

Q2.Which one of the following statements about the reaction below is false?
[Cu(H2O)6]2+ + EDTA4−  [Cu(EDTA)]2- + 6H2O
A       [Cu(EDTA)]2− is a more stable complex than [Cu(H2O)6]2+
B       Both [Cu(H2O)6]2+ and [Cu(EDTA)]2− are octahedral complexes.
C       There is an increase in entropy when the reaction occurs.
D       There is a redox reaction.
(Total 1 mark)

Q3.Complexes containing transition elements have a wide variety of uses including acting as dyestuffs like Prussian Blue.
Cisplatin is a platinum-based chemotherapy drug used to treat various types of cancers. It was the first member of a class of anti-cancer drugs that react with DNA in tumour cells.
Cisplatin is prepared from K2PtCl4 according to the following scheme.
All the reactions shown are reversible.

(a)     Name the type of reaction occurring in all four steps of the scheme.
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(1)
(b)     Explain why an excess of potassium iodide is used in Reaction 1.
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(2)
(c)     (i)      Write an equation for Reaction 1.
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(1)
(ii)     Calculate the percentage atom economy for the formation of K2PtI4 in Reaction 1. 
Show your working.
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(2)
(d)     In Reaction 3, silver nitrate solution is added to improve the yield of product.
(i)      Write the simplest ionic equation for the reaction of iodide ions with silver nitrate.
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(1)
(ii)     Suggest why addition of silver nitrate improves the yield of product from Reaction 3.
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(1)
(e)     Suggest two reasons, other than poor practical technique, why the overall yield of cisplatin in this synthesis may be low.
Reason 1 .......................................................................................................
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Reason 2 .......................................................................................................
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(2)
(f)     The cisplatin formed in Reaction 4 is impure. Outline how the impure solid is purified by recrystallisation.
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(3)
(g)     Platinum compounds are highly toxic.
(i)      State why cisplatin is used in cancer treatment despite its toxicity.
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(1)
(ii)     Suggest a suitable precaution that should be taken by medical staff when using cisplatin.
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(1)
(Total 15 marks)

Q4.(a)     Some metal ions are toxic to humans. A substance that can be used to treat such poisoning contains the ion EDTA4–. 
EDTA4– forms very stable complexes with metal ions. These complexes are not toxic.
(i)      Write an equation for the reaction of EDTA4– with aqueous copper(II) ions, [Cu(H2O)6]2+.
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(1)
(ii)     A solution containing EDTA4– can also be used in a titration to determine the concentration of metal ions in solution. 
A river was polluted with copper(II) ions. When a 25.0 cm3 sample of the river water was titrated with a 0.0150 mol dm–3 solution of EDTA4–, 6.45 cm3 were required for complete reaction. 
Calculate the concentration, in mol dm–3, of copper(II) ions in the river water. 
Show your working.
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(2)
(b)     The determination of the concentration of copper(II) ions in a single sample of river water gives an unreliable value for the copper(II) ion pollution in the river. 
Give one reason why this value is unreliable.
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(1)
(c)     Silver complexes can be used to identify a particular organic functional group. 
Give one example of a silver complex that can be used in this way and state the organic functional group it identifies.
Silver complex ...............................................................................................
Organic functional group ...............................................................................
(2)
(Total 6 marks)

Q5.          Transition metals form complex ions. Using actual examples of complex ions formed by transition metal ions, give the formula of
•   a linear complex ion,
•   a tetrahedral complex ion and
•   an octahedral complex ion formed by using a bidentate ligand.

(Total 4 marks)
Q6.          (a)     The ion  can act as a bidentate ligand.
(i)      Explain the meaning of the term bidentate ligand.
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(ii)     Sketch the structure of the octahedral complex ion formed by Fe3+ ions which contains  as the only ligand. Include the overall charge on the complex ion.

 

 
(5)
(b)     Explain the meaning of the term chelate effect.
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(2)
(c)     The chloride ion can act as a monodentate ligand.
(i)      Deduce the formula of the linear complex formed when an excess of concentrated hydrochloric acid is added to silver chloride.
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(ii)     Explain why metal(II) ions do not usually form octahedral complexes when chloride ions are the only ligands.
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(2)

 

M1.C
[1]

M2.D
[1]

M3.(a)     (ligand) substitution
Allow ‘ligand exchange’.
1

(b)     To displace the equilibrium to the right
To ensure reaction goes to completion.
1

To improve the yield
Allow ‘to replace all chlorines’.
1

(c)     (i)      K2PtCl4  +  4Kl  →  K2Ptl4  +  4KCl
Allow correct ionic equations PtCl42−  +  4l−  →  Ptl42−  +  4Cl−
Allow multiples and fractions.
1

(ii)     = (780.9) ×100 / (415.3  +  664)
Working must be clearly shown.
Allow one mark for correct relationship even if Mr values are incorrect eg using values from ionic equation.
1

= 72.4
Allow 72%
1

(d)     (i)      Ag+  +  I−  →  AgI
Ignore state symbols even if incorrect.
This equation only.
1

(ii)     Stops the reverse reaction / equilibrium displaced to the right
1

(e)     Number of steps in the process
Allow ‘equilibrium may lie on the reactant side’ / side reactions / isomer formation.
1

Losses at each stage of the synthesis
Equilibrium losses or practical losses or yield not 100% for each step.
1

(f)     Minimum amount of hot solvent
Accept ‘small’ for minimum.
Accept water.
1

Cool / crystallise
1

Filter
1

(g)    (i)      Small amounts are more likely to kill cancer cells rather than the patient
1

(ii)     Wear gloves / wash hands after use
Ignore masks.
Apply the list principle if more than one answer.
1
[15]

M4.(a)     (i)      EDTA4−  +  [Cu(H2O)6]2+  →  [Cu(EDTA)]2−  +  6H2O
1

(ii)     (Mol EDTA = (6.45/1000) ×0.015 = )9.68 ×10−5 mol Cu(II)
1

Conc. Cu(II) = ((9.68 ×10−5) / 0.025 =) 0.00387 mol dm−3
Correct answer without working gains M2 only.
1

(b)     Samples may not be consistent throughout the river
OR
Concentration may vary over time
Ignore comments on technique.
1

(c)     [Ag(NH3)2]+
Accept name eg diamminesilver(I) ion.
1

aldehyde
Allow CHO.
1
[6]

M5.          Linear complex             e.g.        [Ag(NH3)2]+ (1)
          Tetrahedral complex     e.g.        [CoCl4]2– (1)
          Octahedral complex     e.g.        [Fe(H2NCH2CH2NH2)3]3+
Species (1)
Charge (1)
[4]

 

M6.          (a)     (i)      Two (1) lone pair donor / electron pair donor (1) atoms
Allow:– forms two co-ordinate bonds (1)
NOT atom with two lone pairs

(ii)     

Correct ligand structure (1) 
penalise any error
Six correct O–Fe bonds (1)
Correct charge (1)
N.B. Penalise the second mark if arrow from Fe shown
N.B. Ignore charges on atoms
5

(b)     (Substitution of a monodentate ligand by a) bi or multidentate
ligand (1) giving a more stable complex (1) or with an increase
in entropy / disorder or forming a ring / cage complex / structure
(crab like)
2

(c)     (i)      [AgCl2]– or AgCl2– (1)

(ii)     Chloride or Cl– big or large or repel (1)
NOT Cl2 or Cl+ or Cl
Allow ‘chlorine ion’
2

(d)     (i)      (Both) ions are negative or ions repel or High Ea (1)

[14]