Define the term standard electrode potential. ........................................................................................................................................................... .........................................................................................................................................................

1. (a)(i)Define the term standard electrode potential. ........................................................................................................................................................... .........................................................................................................................................................[2]
2. (a)(ii)Three redox systems, A, B and C, are shown. The ligand 1,2-diaminoethane, H2NCH2CH2NH2, is represented by en. A [Ru(H2O)6]3+ + e¯ ⇌ [Ru(H2O)6]2+ B [Ru(NH3)6]3+ + e¯ ⇌ [Ru(NH3)6]2+ C [Ru(en)3]3+ + e¯ ⇌ [Ru(en)3]2+ Two electrochemical cells are set up to compare the standard electrode potentials, E°, of three half-cells. The diagrams show the relative potential of each electrode. [Figure showing two electrochemical cells comparing different Ru complexes] Use this information to complete the table by adding the labels A, B and C to deduce the order of E° for the three half-cells. E° redox system most negative least negative[1]
3. (a)(iii)The complex [Ru(en)3]3+ shows stereoisomerism. The ligand en is bidentate. Draw three-dimensional diagrams to show the two isomers of [Ru(en)3]3+. Represent the ligand en by using N N Name the type of stereoisomerism.[3]
4. (b)(i)An electrochemical cell consists of a Br2/Br-half-cell and a Ag+/Ag half-cell, under standard conditions. Use the Data Booklet to calculate the E°cell. Deduce the direction of electron flow in the wire through the voltmeter between these two half-cells. E°cell = ...................................................................................................................... V direction of electron flow from ............................................................. to .............................................................[1]
5. (b)(ii)Water is added to the Ag+/Ag half-cell in (b)(i). Suggest the effect of this addition on the E°cell. Place a tick (✔) in the appropriate box. less positive no change more positive Explain your answer. ........................................................................................................................................................... ...........................................................................................................................................................[2]
6. (c)(i)Silver bromide, AgBr, dissolves in an aqueous solution of S2O32- ions to form the complex ion [Ag(S2O3)2]3-. The S2O32- ions act as monodentate ligands. equilibrium 1 AgBr(s) + 2S2O32-(aq) ⇌ [Ag(S2O3)2]3-(aq) + Br-(aq) Define the term ligand.[1]
7. (c)(ii)Write an expression for the equilibrium constant, Kc, for equilibrium 1. Kc = .................................................................................................................................................[1]
8. (c)(iii)Some additional data are given about the dissolution of AgBr in S2O32-(aq). equilibrium constant solubility product, Ksp, of AgBr stability constant, Kstab, of [Ag(S2O3)2]3- numerical value 5.4 x 10-13 2.9 x 1013 Use your answer to (c)(ii) and these data to calculate Kc for equilibrium 1. Include the units for Kc. Kc = .......................................................................... units ...........................................[2]
9. (d)The numerical values for the stability constants, Kstab, of two other silver(I) complexes are given. silver(I) complex [Ag(CN)2]- [Ag(NH3)2]+ numerical value of Kstab 5.3 x 1018 1.6 x 107 An aqueous solution containing Ag+ is added to a solution containing equal concentrations of CN-(aq), NH3(aq) and S2O32-(aq). The mixture is left to reach equilibrium. Deduce the relative concentrations of [Ag(CN)2]-, [Ag(NH3)2]+ and [Ag(S2O3)2]3- present in the resulting mixture. Explain your answer. highest concentration ............................................... > ............................................... > ............................................... lowest concentration[2]

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