Gold is an unreactive metal that can only be oxidised under specific conditions. Some relevant half-equations and their standard electrode potentials are given. | | half-equation | Eº/V | |---|-------------------------------------------------|--------| | 1 | Au³⁺(aq) + 3e⁻ ⇌ Au(s) | +1.50 | | 2 | [AuCl₄]⁻(aq) + 3e⁻ ⇌ Au(s) + 4Cl⁻(aq) | +1.00 | | 3 | NO₃⁻(aq) + 4H⁺(aq) + 3e⁻ ⇌ NO(g) + 2H₂O(l) | +0.96 |

1. (a)(i)Define the term standard electrode potential.[2]
2. (a)(ii)Draw a fully labelled diagram of the apparatus that should be used to measure the standard cell potential, E°cell, of Au³⁺(aq)/Au(s) and HNO₃(aq)/NO(g). Include all necessary chemicals.[4]
3. (a)(iii)Write an ionic equation to show the spontaneous reaction that occurs when an electric current is drawn from the cell in (a)(ii).[1]
4. (a)(iv)Calculate the E°cell of the reaction in (a)(iii). E°cell = V[1]
5. (a)(v)Gold can be oxidised by a mixture of concentrated hydrochloric acid and concentrated nitric acid, known as aqua regia. Concentrated hydrochloric acid is 12 moldm⁻³. Concentrated nitric acid is 16 moldm⁻³. Explain why aqua regia is able to dissolve gold. In your answer, state and explain what effect the use of concentrated hydrochloric acid and concentrated nitric acid have on the E values of half-equations 2 and 3.[3]
6. (b)(i)Write an equation for the reaction of AuCl₃ with H₂O₂.[1]
7. (b)(ii)Determine the rate equation of the reaction. Show your reasoning, quoting data from the table. | experiment | [AuCl₃] /mol dm⁻³ | [H₂O₂] /mol dm⁻³ | rate of production of O₂(g) /dm³ minute⁻¹ | |------------|-------------------|-------------------|---------------------------------------| | 1 | 0.05 | 0.50 | 7.66 × 10⁻² | | 2 | 0.10 | 0.50 | 1.53 × 10⁻¹ | | 3 | 0.15 | 1.00 | 4.60 × 10⁻¹ |[3]
8. (b)(iii)Use the results of experiment 2 to calculate the value of the rate constant, k, for this reaction. Include the units of k. rate constant, k = units =[2]
9. (c)(i)Name the enthalpy changes labelled ∆H₄ and ∆H₆. ∆H₄ = ∆H₆ =[2]
10. (c)(ii)Use the data in the table and data from the Data Booklet to calculate the lattice energy of AlF₃. | process | enthalpy change /kJ mol⁻¹ | |---------------------------------|---------------------------| | Al(s) → Al(g) | +326 | | Al(g) → Al³⁺(g) | +5137 | | F(g) → F⁻(g) | -328 | | Al(s) + 1.5F₂(g) → AlF₃(s) | -1504 | lattice energy of AlF₃ = kJ mol⁻¹[2]
11. (c)(iii)Scandium fluoride, ScF₃, is an ionic compound. Use data from the Data Booklet to suggest how the lattice energy of AlF₃ compares with the lattice energy of ScF₃. Explain your answer.[2]
12. (d)(i)AlF₃ is sparingly soluble in water. The concentration of its saturated solution at 298K is 6.5 × 10⁻² mol dm⁻³. Write an expression for the solubility product, Ksp, of AlF₃. Ksp =[1]
13. (d)(ii)Calculate the numerical value of Ksp for AlF₃ at 298 K. Ksp =[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.