Question

(b) Oxalate (C2042) binds strongly to many transition metals, including iron, in lower oxidation states but not at all to their anionic oxoanions (e.g. [FeO4]2). The Frost diagram for Fe is given below (note that the numbers in parentheses corresponds to the vE values for the different species). The overall equilibrium (stability) constant for formation of [Fe(C204)j* is ß3 = 10193. 6 FeOj (5.89) 4 2 Fe (0) Fe (-0.11) Fe (-0.88) 2 6 Oxidation number Use the information above to calculate E([Fe(C2O4)s]*/ Fe) Will [FeO4]2 be a stronger oxidising agent if oxalic acid is added to the solution? Explain your answer [Hint: use the value of E([FeO.]P/ [Fe(C20.)3]^)] (i) (ii vE/V

Answer 1

1. Using the equation n. F. E = R. T. lnK , where K is formation constant or stability constant. We get E = RT ln K /nF

E = 8.314 * 298 ln(10^19.3) / 3*96500

= 0.38 V

This is the required E.

2. From the graph the E value of (FeO₄)^2- = 6V.

E of ((FeO₄)^2- /(Fe(C2O4)3)^3- = 6 - 0.38 = 5.62 V. Adding oxalic acid to the solution decrease the E value. As a result of which it's reducing power decreases and oxidising power increases.