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# how to get the oxidation number of an element in a compound?

can someone please explain me his step by step in an easy way

### 1 Answer

- 8 years agoFavorite Answer
Okay, let's start with a simple one: H2O

The general rule is that O (oxygen) has an oxidation number (O.N) of -2 in a compound, meaning the H2 needs an O.N of +2 to cancel it out, because the overall charge here is 0. BUT there are TWO H's, so each one has an O.N of +1.

So, we have: H2O: (+1)2 + (-2)= 0

But what about something like, say... CoCl2+?

We know that Cl (chlorine) anions have a -1 charge, so we'll start there. If each chlorine has a -1 O.N, and there's 2 Cl's that gives them a -2 charge. BUT the O.N's of a compound MUST add up to the total charge of the compound.

As this compound has an overall charge of +1: O.N(Co) -2 = 1

.: O.N (Co) = +3

That's as simple as I can get it, hope it's helped

Source(s): Studying Chemistry at university