1)
Both the hexa–aqua ions of iron(II) and iron(III) readily
complex with EDTA
-
[Fe(H2O)6]2+(aq)
+ EDTA4–(aq) ===>
[Fe(EDTA)]2–(aq) +
6H2O(l)
                        Â
Kstab =
{[Fe(EDTA)3]2–(aq)}
/
{[Fe(H2O)6]2+(aq)}
[EDTA4–(aq)]
                       Â
Kstab = 2.0 x 1013 mol–1
dm3and lg(Kstab) =
14.3
-
[Fe(H2O)6]3+(aq)
+ EDTA4–(aq) ===>
[Fe(EDTA)]–(aq) +
6H2O(l)
                      Â
Kstab =
{[Fe(EDTA)3]–(aq)}
/
{[Fe(H2O)6]3+(aq)}
[EDTA4–(aq)]
                      Â
Kstab = 1.3 x 1025 mol–1
dm3and lg(Kstab) =
25.1
Note that the more highly charged
Fe3+(aq) ion complexes more
strongly than the Fe2+(aq)
ion.
2) iron 3 will interfere
