Knowing oxidation states

[CHEM 14B Lover]

In HW, 6L 1.9, it says the balance the reaction between potassium permanganate and iron2 chloride. How do we know the change in manganese's oxidation state (from +7 to +2)? Should we just know? +7 is deducible but not +2 (I think).

[aisteles1G]

You have to look at the charge of the atom it's paired with so KMnO4 is +7 bc k is +1 and 0 is -2*4=-8 and the overall charge of the compound is zero so Mn has to be +7 to cancel the others out to zero. I'm not sure what the +2 compound is that you're referring to bc i dont have the book with me but if it's MnO then O is -2 so Mn has to be +2 to make the overall charge 0 of the compound. Hope this helps!

[Emily Huang 1E]

You have to look at what Manganese is bonded to.KMnO4 is the compound and based on the periodic table we know the oxidation state of K is 1+ and the oxidation state of O is 2-. You can figure out an unknown oxidation number by knowing the oxidation number of the element it is bonded to