I really need to know because my grade in science kind of sucks and my teacher definitley never went over this.
pH = -log(molar concentration of H)
So first you need to calculate the concentration of H. There should be tables or a list of solubility constants that tell you this. As for solubility constants it means the concentration of one molecule times the concentration of the other molecule equals the constant. So if you know the concentration of one you can figure out the concentration of the other.
Or if you already know the concentrations of H and OH then its a lot easier. -log (concentration of H) and -log(concentration of OH). H3O is H bonded to H20, and all H's are actually bonded to H2O, so it's really the same thing as concentration of H.
well OH ions form alkali solutions therefore it would be above ph 8 depending on the concentrations, and H3O would be below ph 6 depending on the concentrations as well. hope this helps :)