Question

What are the oxidation numbers of Fe, N and O in the compound Fe(NO3)3?

Answer 1

Oxidation number is the charge left on the central atom, when all the bonding electrons are removed with the charge devolving to the most electronegative atom.

Explanation:

Clearly the oxidation number of the iron centre is `III+`, as 3 nitrate ions are bound to this centre:

`Fe(NO_3)_3rarrFe^(3+) + 3NO_3^-`;

Now to determine the oxidation state of nitrogen, we know that `3xxON_(O)+ON_N = -1`. Why? Because the sum of the oxidation numbers must equal the charge on the ion. `ON_(O)` is normally `-II`, and it is here, so `3xx(-2)+ON_N = -1`. Oxidation number of nitrogen is `V+`.

I would have got the same result had I used the definition of oxidation state, i.e. `NO_3^(-) rarr N^(5+) + 3xxO^(2-)`.

What are the oxidation states of the metal in `FeCl_4^-`, `MnO_4^-`, and `Cr_2O_7^(2-)`?