Question

What is the oxidation number of iron in Fe3O7 ?

Answer 1

In `Fe_3O_7` Iron has an Oxidation Number of `4 2/3`

Explanation:

Oxidation numbers are calculated through a set of rules. Oxygen is an atom that has only 3 possible Oxidation numbers:

1. If Oxygen is bonded to itself (Mainly in `O_2` ) then it has an Oxidation number of 0. This is true of any atom that bonds to itself with few exceptions.
2. If Oxygen is in the form of Peroxide `O_2^-2` then it will have an oxidation number of -1.
3. In all other cases Oxygen will have an Oxidation Number of -2.

Since your molecule has Iron bonded to Oxygen and that Oxygen is not in the form of Peroxide. It follows that each Oxygen has an Oxidation number of -2.

That gives all of the Oxygen a cumulative Oxidation Number of -14. All molecules must have a Net Oxidation Number equal to their charge (in this case 0). Meaning that the 3 Irons must add up to +14 cumulatively.

Simple division then leads you to determine that the +14 distributed across 3 Iron atoms will have an Oxidation number of `14/3` or `4 2/3`.