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

1 Answer
Dec 26, 2016

Answer:

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]^("-")#.