Question

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

Answer 1

You use the rules for oxidation numbers to calculate that the oxidation number of `"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 `"NO"_3^"-"`.

Rule 1 tells us that the oxidation number of `"O"` is -2: `["N" stackrelcolor(blue)("-2")("O")_3]^("-")`.

The three `"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 `"N"`.

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

`x = "-1" - "(-6)" = "-1 + 6" = +5`

∴ The oxidation number of `"N"` is +5: `[stackrelcolor(blue)("+5")("N")stackrelcolor(blue)("-2")("O")_3]^("-")`.