Question

What is the oxidation number of nitrogen in the nitrate ion NO31−?

+6

+5

+3

+2

Answer 1

In No3-1 the oxidation number of oxygen is -5 so oxidation number of N would be +5

Answer 2

Oxidation state on
`\text{N}` as in the nitrate ion
`{\text{NO}_3}^(-)`: +5.

Step-by-step 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
  `\text{O}_2`: 0.
• Oxidation state of O in
  `\text{H}_2\text{O}_2` 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
`3 * (-2) = -6`.

The oxidation state of the N atom needs to be found. Charge on the nitrate ion is -1. Thus

`\begin{array}{ccc}\text{oxidation state on all atoms in the ion}&= &\text{charge of the ion}\\(\text{oxidation state on N}) + 3 * (-2) &=& -1\end{array}`

`(\text{oxidation state on N}) = -1 - 3*(-2) = -1 - (-6) = -1 + 6 = +5`.

Therefore, the oxidation state of the nitrogen N atom in the nitrate ion
`{\text{NO}_3}^(-)` is +5.