this is what i have done and it has always worked. there are rare instances when, for example, H is not +1, but it will be pretty obvious, because it'll be paired up with something you know is always positive. i doubt they'll try to throw you for a loop on the mcat like that though. just have an idea of the anions/cations that are (almost) always the same (e.g. H1+, Na1+, Cl1-, Br1-) etc... and you should be able to figure it out from there. then look at the subscript. If it's Cl2, you know the charge is -2 and that the oxidation number of the other element is +2 if it's a single element, +1 if it's 2 together.Originally posted by AlternateSome1
Hmm...don't feel bad, its not that easy. Basically you start with what you know, and work from there. Generally you will know that one compound ALWAYS takes a certain oxidation state...such as Cl -. Then you figure out what possible numbers could fit for the other oxidation state so that they total 0 (or the oxidation state superscript given!). So...AgCl. Maybe you have no idea what silver's oxidation states are, so you start with knowing Cl is -1. Then you determine that you have no overall charge. Therefore, Ag must be +1. I hope this helps at all.