Oxidation Number Assigning

Question

Determine the oxidation number of Mn in MnO-4. 

Answer 1

Hello Brenda, the charge on the permanganate ion is 1-.  If you assign 2- to oxygen times 4 atoms, you get 8-.  You then have to assign 7+ to the manganese atom to net 1- for the ion overall.

Answer 2

The correct formula would be MnO₄^-, so it has a net charge of minus 1, not -4.

We know that each O has an oxidation number of 2- (you just have to memorize that).

There are a total of 4 oxygens, so that will be a charge of -8.

In order to have an overall net charge of -1, the Mn must have an oxidation number of 7+.

Thus, 7+ for Mn and 8- for the oxygens results in -1 overall.