Question

What is `Fe_3O_4`, and how do we represent its formation from iron, and water?

Answer 1

This is a mixed valence oxide of `FeO` and `Fe_2O_3`........

Explanation:

In the original redox reaction, elemental iron is OXIDIZED to `FeO + Fe_2O_3`, i.e. `FeO*Fe_2O_3-=Fe_3O_4`.

And so we write 2 separate oxidation rxns....

`Fe +H_2O rarr FeO+2e^(-) +2H^+`, and....

`2Fe +3H_2O rarr Fe_2O_3+6H^(+) + 6e^(-)`

We adds these together and get.....

`3Fe +4H_2O rarr underbrace(Fe_2O_3+FeO)_(Fe_3O_4) +8H^(+) + 8e^(-)` `(i)`

And for every oxidation, electron loss, there is a corresponding reduction, electron gain, and the most likely oxidant is dioxygen gas.....

`1/2O_2 + 2H^+ + 2e^(-)rarrH_2O` `(ii)`

And so we take `4xx(ii)+(i)` to eliminate the electrons from our final redox equation.......

`3Fe +2O_2 + cancel(4H_2O +8H^(+) + 8e^(-)) rarr underbrace(Fe_2O_3+FeO)_(Fe_3O_4) +cancel(8H^(+) + 8e^(-)+4H_2O)`

To give finally.......

`3Fe +2O_2 rarr underbrace(Fe_2O_3+FeO)_(Fe_3O_4)`

`Fe_3O_4` is a mixed valence iron oxide.....`Fe_2O_3*FeO`