oxidation number rules?

[joonkimdds]

I don't know if the way I find Oxidation number is right or wrong.

Here is an example.
FeSO4

The way I do this problem is first, I always count H and O first.(is that right?)
I need to memorize that O is always -2.
so -2 x 4 = -8.

and 2nd, I need to read it from right to left. Since O is all the way to the right, I did O first. Now is time to get S.
S is at 6th group so it's +6.

-8+6 = -2
so Fe is 2.

I don't know if these are the right way of getting the oxidation number.

and besides O = -2, what else should I memorize? and why can't S be -2 just like oxygen even though they are belonging to the same group?

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[Wonder1024]

Seems okay to me. The only thing I do differently is use algebra. For instance, if you want to find the oxidation number of Fe, I set it to "x". Then I follow the same procedure as you, using the subscripts and oxidation numbers I already know (i.e. O and S). Then I add everything up. Since there is no net charge on the compound FeSO4 (i.e. it's neutral, or 0), the sum of each element’s contribution is 0. So, I write

X + (-8) + (+6) = 0
X = +2

Your way is still correct, I believe. I just do it this way, in case you’re given a compound with some kind of net charge (in which case, the sum would be the overall charge, and not 0). I'm not sure, but I think the Kaplan blue book has a list of important oxidation numbers you should know.

 

[Albuterol]

O is not Always -2..it is most of the time except when in a peroxide H2O2 then it is -1.

Memorize H is always +1 and work your way from there.
Group IA and IIA metals form +1 and +2 respectively

S cannot always be -2 because it can expand its octet since it is a 3 period element.
SO2- S +4
H2S- S -2

 

[Andre3k]

SO4 as a group will always be -2 (at least from my experience). So Fe is +2 .

 

[wbloo]

I know that all the halogens have a -1 charge and that oxygen has a -2 charge, and H is +1.

Also, Group IA is +1 and Group 2A is +2

Transition metals have muiltiple oxidation states - so if you need to find one, figure out all the other oxidation states in the molecule and have it equal to zero to solve, unless the molecule has a negative or positive charge, then adjust accordingly..

 

[Albuterol]

http://www.seas.upenn.edu/~chem101/oxidationstates.html

 

[jjw822]

S is at 6th group so it's +6.

is this right???

i thought we we were suppose to look at SO4 which is -2...

i dont get that... 6th group = +6//

 

[Albuterol]

+6 so S is the maximum oxidation number it can attain
-2 is the minimum oxidation number it can attain

SO2--
x + 2(-2) = -2
x= +2