I apologize for my "noobie" question. I've been using Moodle for my chemistry students. We are currently going over Acids, Bases, and pH. For the pH calculations, I have no problem of converting the concentration to pH (using the log10 calculation), but I'm having difficulties reversing the calculation (using antilog, [H3O+]=10^-pH).
In many Moodle plugins, "log" is natural log. When it is:
pH = log(H3O+)/log(10)
You can check it works by doing 10^pH. Some plugins prefer something like power(10,pH). You need to see the documentation for the specific plugin.