How do you calculate the oxidation number of an ion?

1 Answer
anor277
Aug 19, 2016

For simple ions, i.e. Na^+, Cl^-, Fe^(2+), Fe^(3+), the oxidation number of the element is simply the charge on the ion.

Explanation:

For more complex ions, the SUM of the oxidation numbers equals the charge on the ion. The sum of the oxidation numbers also equals the charge on the molecule in a NEUTRAL molecule.

Let's consider Cl^-, ClO_2, ClO_4^-. Typically the oxidation number of oxygen in its oxides is -II, and it is here in these examples.

Given what I have said the oxidation number of Cl in chloride ion, Cl^-, is -I. The oxidation number of Cl in ClO_2 is +IV, and the oxidation number of Cl in perchlorate, ClO_4^-, is +VII.

I don't what level you are at. If you are at A level, you simply have to know what I wrote in the opening statement. If you are an undergrad you do have to know how to assign oxidation states in more complicated molecules and ions. Good luck.

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