This should mean you want your base to have a pH of 13.5. I don\'t know what material you are starting with but lets say its a base then you know: pOH = 14-pH = 0.5 Thus, pOH = -log[OH-] [OH-] = 10^-0.5 And you know concentration is expressed in mol/L so you can easily calculate volume consequently. Please don\'t forget to rate, good luck studying! Solution This should mean you want your base to have a pH of 13.5. I don\'t know what material you are starting with but lets say its a base then you know: pOH = 14-pH = 0.5 Thus, pOH = -log[OH-] [OH-] = 10^-0.5 And you know concentration is expressed in mol/L so you can easily calculate volume consequently. Please don\'t forget to rate, good luck studying!.