Ethanedioate ions, ⁻O₂CCO₂⁻, are bidentate ligands. The abbreviation ed²⁻ can be used to represent ethanedioate ions.

1. (a)Complete the following electronic structures. • the iron atom, Fe 1s²2s²2p⁶ .............................. • the iron(III) ion, Fe³⁺ 1s²2s²2p⁶ ..............................[1]
2. (b)Solutions of iron(III) salts are acidic due to the equilibrium shown. [Fe(H₂O)₆]³⁺(aq) ⇌ [Fe(H₂O)₅(OH)]²⁺(aq) + H⁺(aq) Kₐ = 8.9 × 10⁻⁴ mol dm⁻³ Calculate the pH of a 0.25 mol dm⁻³ FeCl₃ solution. pH = ..............................[2]
3. (c)(i)What is meant by the term stability constant, Kstab?[1]
4. (c)(ii)Use the data in the table to predict the formula of the complex formed in the greatest amount when • a solution containing equal concentrations of both F⁻ and SCN⁻ ions is added to Fe³⁺(aq), • a solution containing equal concentrations of both Fe³⁺ and Hg²⁺ ions is added to Cl⁻(aq).[1]
5. (d)The complex [Fe(ed)₂Cl₂]³⁻ can be formed according to the equation shown. [Fe(H₂O)₄Cl₂]⁺(aq) + 2ed²⁻(aq) ⇌ [Fe(ed)₂Cl₂]³⁻(aq) + 4H₂O(l) Write the expression for the equilibrium constant, Kstab, and state its units. Kstab = .............................. units ..............................[2]
6. (e)(i)Complete the three-dimensional diagrams to show the three stereoisomers of [Fe(ed)₂Cl₂]³⁻. You may use [symbol for ethanedioate] to represent ed²⁻.[3]
7. (e)(ii)Give the letters of two isomers of [Fe(ed)₂Cl₂]³⁻ which are geometrical isomers of each other.[1]
8. (e)(iii)Give the letters of the two isomers of [Fe(ed)₂Cl₂]³⁻ which show optical isomerism.[1]
9. (e)(iv)Give the letter of the isomer which has no dipole moment.[1]

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