The pH of a solution is defined as the negative logarithm of the hydrogen ion (H+) concentration. We can use this definition to calculate the pH of a solution with a given [H3O+] concentration.
pH = -log([H3O+])
[H3O+] = 10.33 x 10^-9 M
pH = -log(10.33 x 10^-9)
pH = -log(10.33) - log(10^-9)
pH = -log(10.33) + 9
pH = 9 - log(10.33)
Approximating log(10.33) to 2 decimal places, we have:
pH = 9 - log(10.33) = 9 - 0.016 = 8.984
So the pH of the solution is approximately 8.984