(a) Iron can form stable ions in the +2 and +3 oxidation states. Explain why transition elements have variable oxidation states. [1] (b) Aqueous solutions of iron(II) salts contain the complex ion [Fe(H2O)6]2+. Define complex ion. [1] (c) [Fe(H2O)6]2+ can be converted into [Fe(H2O)4(OH)2]. (i) Suggest a suitable reagent for this conversion. State the type of reaction. reagent type of reaction [1] (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] (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. AG = .............................................. kJ mol⁻¹ [2]