Here’s a mini-tutorial of calculating oxidation numbers.
I’m assuming if you are here, you would at least be able to calculate the oxidation state of copper in CuSO4.
If you were not sure, SO4 have a charge of 2-, so in order to have a neutral compound, Cu have to have a charge of 2+.
In other words, we know that the compound CuSO4 is neutral as written ( charge = 0 ), we know that the SO4 is 2-, but we are not sure about Cu. Therefore we can write:
X + (-2) = 0
X = 0 – (-2)
X = 2
Now calculating the oxidation state of a coordination complex is the same idea. Let’s do it by example.
[Cu(H2O)6]SO4
We know:
H2O have a charge of 0.
There are 6 H2Os.
SO4 have a charge of -2.
We do not know Cu. We write X.
The whole compound is neutral.
We can write:
X + 6(0) + (-2) = 0
X + (-2) = 0
X = -2
So we know that we are working with Copper (II).
Lets try another one.
[CoBr2Cl2]2-
We know:
Total charge is -2
There are 2 Br’s
Each Br has a charge of -1.
There are 2 Cl’s
Each Cl has a charge of -1.
Co we don’t know. Let it be X.
We then can write:
X + 2(-1) + 2(-1) = -2
X -4 = -2
X = 2
So we know that we are using Cobalt (II).