OCR A Jan 2011 Paper 5 Q2

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Iron and platinum are transition elements. They both form ions that combine with ligands to form complex ions. Some of these complexes are important in biological systems. (a) Complete the electron structures of: an atom of Fe: 1s22s22p6an ion of Fe2+: 1s22s22p6[2] (b) State one property of Fe2+, other than the ability to form complex ions, which is typical of an ion of a transition element.[1] (c) Aqueous iron(II) sulfate takes part in redox reactions. Using oxidation numbers, show that both reduction and oxidation have taken place in the redox reaction of aqueous iron(II) sulfate shown below. 6FeSO4 + 7H2SO4 + Na2Cr2O7 3Fe2(SO4)3 + Cr2(SO4)3 + Na2SO4 + 7H2O[2]OCR 2011<br />
 (d) Hexaaquairon(II) ions, [Fe(H2O)6]2+, take part in a ligand substitution reaction with ammonia. [Fe(H2O)6]2+(aq) + 6NH3(aq) [Fe(NH3)6]2+(aq) + 6H2O(l) Write an expression for the stability constant, Kstab, for this equilibrium. (e) Haemoglobin is a complex of iron(II). (i) Explain how ligand substitutions allow haemoglobin to transport oxygen in the blood. [2][2] (ii) In the presence of carbon monoxide, less oxygen is transported in the blood. In terms of stability constants, suggest why.[2]OCR 2011 Turn over<br />
 (f) Platin, Pt(NH3)2Cl2, is a complex of platinum(II) that has two stereoisomers. One of these stereoisomers is used in medicine. (i) Platin is a neutral complex. Explain why platin is neutral.[1] (ii) Draw diagrams of the two stereoisomers of platin and describe its bonding.[3] (iii) Describe the action of platin in the treatment of cancer patients.[1]OCR 2011<br />
 (g) The use of platin in medicine can cause unpleasant side effects for patients. In the search for alternatives, chemists often start with the current drug and modify its properties by chemically changing some of the groups. A recent discovery is a drug called carboplatin. The structure of carboplatin is similar to platin except that a single 1,1-cyclobutanedicarboxylate ion replaces the two chloride ligands in the structure of platin. Draw the structures of,the 1,1-cyclobutanedicarboxylate ion carboplatin. 1,1-cyclobutanedicarboxylate ionOCR 2011 carboplatin [2] [Total: 18] Turn over<br />

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