Final Exam

December 21, 2000

6. B. Saha and D. M. Stanbury (p. 1294-1300) studied the reaction [Ru(bpy)₃]²⁺ + Cl₂[Ru(bpy)₃]³⁺ + Cl^–. Balance the reaction and estimate E^o for this reaction under standard acidic conditions. Would you expect the reaction mechanism to be inner sphere or outer sphere? Why? bpy = 2,2'-bipyridine.

Answer:

Oxidation:

[Ru(bpy)₃]²⁺[Ru(bpy)₃]³⁺ + e^–

E^o_red = 1.53 V so E^o_ox = –1.53 V (Shriver and Atkins, Appendix 2, page 706)

Reduction:

Cl₂ + 2 e^–2 Cl^–

E^o_red = 1.358 V (Shriver and Atkins, Appendix 2, page 699)

Net:

2 [Ru(bpy)₃]²⁺ + Cl₂2 [Ru(bpy)₃]³⁺ + 2 Cl^–

E^o = E^o_red + E^o_ox

E^o = 1.358 – 1.53 = –0.17 V

The reaction is probably outer sphere because the metal complex has a filled coordination sphere.