What is the oxidation state of Fe in Fe2O3? (A) Minus three, (B) minus two, (C) plus one, (D) plus two, or (E) plus three.
Oxidation states are generally used as a way to keep track of electrons in reduction–oxidation or redox reactions. In this question, we want to find the oxidation state of Fe or iron in Fe2O3, which is called iron three oxide, the compound that’s commonly found in rust. There are a couple of rules about oxidation states that we can use to help us assign oxidation states to both of the elements in this compound.
The first is that oxidation states of the atoms in a compound will always sum to the net charge of the compound. Fe2O3 is neutral, so we would expect the oxidation states of all of the atoms in this compound to sum to zero. The next thing we need to know is that the oxidation state of oxygen is usually minus two. So, the oxidation state of oxygen in iron three oxide is minus two.
And since we have three oxygens in iron three oxide, that means we have a total oxidation state of minus six so far. And since iron three oxide is neutral, we would expect the irons collectively to have an oxidation state of positive six to cancel that out. And since we have two irons in iron three oxide, that means each iron has an oxidation state of plus three. And in this question, we were tasked with finding the oxidation state of iron in iron three oxide, which we found to be plus three, which matches answer choice (E).