Oxidation state on [tex]\text{N}[/tex] as in the nitrate ion [tex]{\text{NO}_3}^{-}[/tex]: +5.
Explanation
The sum of oxidation states on all atoms in an ion should be the same as the charge of the ion.
The oxidation state of nitrogen N tends to vary. However, the oxidation state of oxygen O is -2 in most cases, with the following exceptions:
- Oxidation state of O in [tex]\text{O}_2[/tex]: 0.
- Oxidation state of O in [tex]\text{H}_2\text{O}_2[/tex] and other peroxides: -1.
- The oxidation state of O will be positive when it is bonded to fluorine F.
To find the oxidation state on N, consider the atoms in a nitrate ion:
- There are three O atoms in each nitrate ion, as seen in the subscript "3".
- There's only one N atom in each nitrate ion.
The oxidation state of each O atom is expected to be -2. There are three O atoms in each nitrate ion. The oxidation state of the three atoms will add up to [tex]3 \times (-2) = -6[/tex].
The oxidation state of the N atom needs to be found. Charge on the nitrate ion is -1. Thus
[tex]\begin{array}{ccc}\text{oxidation state on all atoms in the ion}&= &\text{charge of the ion}\\(\text{oxidation state on N}) + 3 \times (-2) &=& -1\end{array}[/tex]
[tex](\text{oxidation state on N}) = -1 - 3\times(-2) = -1 - (-6) = -1 + 6 = +5[/tex].
Therefore, the oxidation state of the nitrogen N atom in the nitrate ion [tex]{\text{NO}_3}^{-}[/tex] is +5.
