OCR A Specimen Paper 3 Q3

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3 This question looks at properties of iron compounds and iron ions in different oxidation states. (a) Fe2+ and Fe3+ are the most common ions of iron. Write the electron configuration, in terms of sub-shells, for the Fe2+ ion. (i)(ii) How many orbitals contain an unpaired electron in an ion of Fe2+?(b) [Fe(H2O)6]3+ ions take part in ligand substitution reactions. An excess of aqueous potassium cyanide, KCN(aq), is added to an aqueous solution containing [Fe(H2O)6]3+ ions. A ligand substitution reaction takes place forming a complex ion that has a molar mass of 211.8 g mol1. Write an equation for this ligand substitution reaction. Specimen [Fe(H2O)5OH]2+(aq) + H+(aq)(c) The complex ion, [Fe(H2O)6]3+, behaves as a weak BrnstedLowry acid in aqueous solution. The equation below represents the dissociation of aqueous [Fe(H2O)6]3+ ions, together with the Ka value. [2] [Fe(H2O)6]3+(aq) (i) Write the expression for the acid dissociation constant, Ka, for [Fe(H2O)6]3+. Ka = 6.00103 mol dm3 (ii) Calculate the pH of a 0.100 mol dm3 solution of [Fe(H2O)6]3+ to two decimal places. [1] [1] [1] pH =[2]OCR 2014 H432/03<br /> (d) Fe2O3 can be oxidised by ClO ions under alkaline conditions in a redox reaction. Unbalanced half-equations for this reaction are shown below. Balance the half-equations and construct an overall equation for the reaction.ClO +H2O +eCl +OHFe2O3 +OHFeO4 2 +H2O +e overall equation:[3] SpecimenOCR 2014 H432/03 Turn over<br />

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