(a) Use appropriate data from Appendix 11 to determine the ratio of the overall stability constants of the complexes [Fe(phen)₃]²⁺ and [Fe(phen)₃]³⁺ at 298 K.

(b) Use the data in Fig. 8.2 to construct a Frost–Ebsworth diagram for manganese in aqueous solution at pH 14. Use your diagram to comment on the stability of [MnO₄]³⁻ under these conditions.

Figure 8.2

Data from Appendix 11

The concentration of each aqueous solution is 1 mol dm⁻³ and the pressure of a gaseous component is 1 bar (10⁵ Pa). (Changing the standard pressure to 1 atm (101 300 Pa) makes no difference to the values of E^o at this level of accuracy.) Each half-cell listed contains the specified solution species at a concentration of 1 mol dm⁻³; where the half-cell contains [OH]⁻, the value of E^o refers to [OH⁻] = 1 mol dm⁻³, hence the notation E^o_{[OH⁻] = 1}

Acidic solution (pH 0) [MnO4] Alkaline solution (pH 14) [MnO] +0.90 +0.56 [HMnO4]- +1.69 [MnO4] +1.51 +2.10 +0.59 +0.27 MnO L +0.95 [MnO4] +0,60 +0.93 Mn+ +1.23 +1.54 MnO Mn+ +0.15 -1.19 -0.04 MnO3 Mn -0.23 Mn(OH) -1.56 Mn