Iodine is found naturally in compounds in many different oxidation states.

1. (a)(i)Identify the role of H2O2(aq) in its reaction with I- ions in acidic conditions. Write an ionic equation for the reaction.[2]
2. (a)(ii)15.0 cm³ of C6H12 is shaken with 20.0cm³ of an aqueous solution containing I₂ until no further change is seen. It is found that 0.390 g of I₂ is extracted into the C6H12. The partition coefficient of I₂ between C6H12 and water, Kpc, is 93.8. Calculate the mass of I2 that remains in the aqueous layer. Show your working.[2]
3. (a)(iii)Suggest how the value of Kpc of I2 between hexan-2-one, CH3(CH2)3COCH3, and water compares to the value given in (a)(ii). Explain your answer.[2]
4. (b)(i)Define enthalpy change of solution.[1]
5. (b)(ii)Use the data in Table 1.1 to calculate the enthalpy change of solution of potassium iodide, KI. Table 1.1 process enthalpy change, ∆H/kJmol⁻¹ K⁺(g) + I⁻(g) → KI(s) −629 K⁺(g) → K⁺(aq) −322 I⁻(g) → I⁻(aq) −293[1]
6. (b)(iii)Suggest the trend in the magnitude of the lattice energies of the Group 1 iodides, LiI, NaI, KI. Explain your answer.[2]
7. (c)(i)A 25.0 cm³ portion of a Cu²⁺(aq) solution reacts with an excess of I⁻(aq). The end-point of the titration occurs when 22.30 cm³ of 0.150 moldm⁻³ S2O3²⁻(aq) is added. Calculate the concentration of Cu²⁺(aq) in the original solution.[2]
8. (c)(ii)Identify a suitable indicator for the titration.[1]
9. (c)(iii)Copper(I) and copper(II) both contain electrons in all five 3d orbitals. Sketch the shape of a 3dxy orbital on the axes provided. [Figure with Z, y, X axes][1]
10. (d)The reaction of I⁻ ions with persulfate ions, S₂O₈²⁻, can be catalysed by Fe³⁺ ions. 2I⁻ + S2O8²⁻ → I₂ + 2SO4²⁻ Write equations to show how Fe³⁺ catalyses this reaction.[2]
11. (e)An orange precipitate of HgI2 forms when Hg²⁺ ions are added to KI(aq). The solubility of HgI2 at 25 °C is 1.00 × 10⁻⁷gdm⁻³. Calculate the solubility product, Ksp, of HgI2. Include units in your answer. [Mr: HgI2, 454.4][3]

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