# How do you determine the oxidation number of nitrogen in the nitrate ion?

Dec 26, 2016

You use the rules for oxidation numbers to calculate that the oxidation number of $\text{N}$ is +5.

#### Explanation:

The important rules here are:

1. The oxidation number of oxygen in a compound is usually -2, except in peroxides, where it is -1.
2. The sum of all the oxidation numbers in a polyatomic ion is equal to the charge on the ion.

The formula of nitrate ion is $\text{NO"_3^"-}$.

Rule 1 tells us that the oxidation number of $\text{O}$ is -2: $\left[\text{N" stackrelcolor(blue)("-2")("O")_3]^("-}\right)$.

The three $\text{O}$ atoms have a total oxidation number of -6.

Rule 2 tells us that the sum of all the oxidation numbers equals the charge on the ion.

Let $x$ = the oxidation number of $\text{N}$.

x +("-6") = "-1"

$x = \text{-1" - "(-6)" = "-1 + 6} = + 5$

∴ The oxidation number of $\text{N}$ is +5: [stackrelcolor(blue)("+5")("N")stackrelcolor(blue)("-2")("O")_3]^("-").