Spinach contains a lot of iron but is not a good source of dietary iron because nearly all the iron is tied up in the oxalate complex [Fe(C2O4)3]3-.
(b) Under the acidic conditions in the stomach, the Fe3+ concentration should be greater because of the reaction
[Fe(C2O4)3]3-(aq) + 6 H3O+(aq) ⇌ Fe3+(aq) + 3 H2C2O4(aq) + 6 H2O(l)
Show, however, that this reaction is nonspontaneous under standard-state conditions. (For H2C2O4, Ka1 = 5.9 × 10-2 and Ka2 = 6.4 × 10-5.)