Why is finding [H+] when given [OH-]= 3.57e-5 M wrong when I use -log[OH-]?
Well You have to note that you cannot simply "e" everything because the base of log in chemistry is base 10 while you assumed that it was all base e. Ie ln(x). in order to get x, we use e, while if we say log(x) we have to assume that it is base 10 which is the general norm