• Oxygen contributes total reduction of (3)(3)(−2) = −18.• Carbon contributes total oxidation of 3(+4) = +12.• Iron contributes total oxidation of 2(+3) = +6.So the oxidation state of Fe 2 (CO 3 ) 3 is (−18) + (+12) + (+6) = 0. This is just what
we would expect. Each iron atom has lost 3 electrons, each oxygen atom has
gained 2 electrons, and each carbon atom has lost 4 electrons. The losses equal
the gains; total oxidation equals total reduction.