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

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Answer 1 · 2016-12-26T21:45:54

You use the rules for oxidation numbers to calculate that the oxidation number of $N$ $"N"$ is +5.

The important rules here are:

The oxidation number of oxygen in a compound is usually -2, except in peroxides, where it is -1.
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 ${NO}_{3}^{-}$ $"NO"_3^"-"$ .

Rule 1 tells us that the oxidation number of $O$ $"O"$ is -2: ${[N {-2 O}_{3}]}_{3}^{-}$ $["N" stackrelcolor(blue)("-2")("O")_3]^("-")$ .

The three $O$ $"O"$ 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 $x$ $x$ = the oxidation number of $N$ $"N"$ .

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

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

∴ The oxidation number of $N$ $"N"$ is +5: ${[+5 N {-2 O}_{3}]}_{3}^{-}$ $[stackrelcolor(blue)("+5")("N")stackrelcolor(blue)("-2")("O")_3]^("-")$ .