What is the pH of a 2.4 x 10-5 M HNO3?

Answer 1

HNO3 is a strong acid that is completely dissociated in dilute solution. Therefore [H+] is the same as [HNO3], and pH is -log[H+]; therefore

pH = -log(2.4*10^-5) = 4.62

Answer 2

HNO3 is indeed a strong solution. Usually, the [H3O+] is just equal to the concentration of HNO3 which in this case is 2.4 x 10-5 M. But in this case, the solution is relatively dilute. I think we used the method of successive approximation for getting the pH. But then again, maybe I'm just causing you trouble. =)