Iron can form stable ions in the +2 and +3 oxidation states.

1. (a)Explain why transition elements have variable oxidation states.[1]
2. (b)Aqueous solutions of iron(II) salts contain the complex ion [Fe(H2O)6]2+. Define complex ion.[1]
3. (c)(i)[Fe(H2O)6]2+ can be converted into [Fe(H2O)4(OH)2]. Suggest a suitable reagent for this conversion. State the type of reaction. reagent _________________________ type of reaction _________________________ [1][1]
4. (c)(ii)[Fe(H2O)4(OH)2] is a green precipitate that turns brown on standing in air. Table 2.1 shows electrode potentials for some electrode reactions. Table 2.1 electrode reaction E°/V Fe(H2O)3(OH)3 + H2O + e¯ = Fe(H2O)4(OH)2 + OH¯ -0.56 O2 + 2H2O + 4e¯ = 4OH¯ +0.40 Use the information in Table 2.1 to explain why [Fe(H2O)4(OH)2] turns brown on standing in air. Include an equation for this reaction.[3]
5. (d)The complex [Co(NH3)6]2+ reacts with hydrogen peroxide as shown. reaction 1 2[Co(NH3)6]2+ + H2O2 → 2[Co(NH3)6]3+ + 2OH- Ecell = +1.67V Calculate ∆G°, in kJ mol-1, for reaction 1. ∆G° = _________________________ kJ mol-1 [2][2]

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