pH is a measure of proton activity and not concentration.
(a) Calculate the pH of water (T = 25oC) containing only 10-7 M H+, i.e. in ultrapure water.
(b) If the same water also contains 0.36 M NaCl, re-calculate the pH. Use the Debye-Huckel equation with A = 0.511 as an approximation to calculate the activity coefficient.
(c) Explain the difference in pH