pH = 3.89

Question

calculate concentration of hydronium ion and hydroxide ion in solution.

Answer 1

pH = -log(H3O^+); solve for H3O^+.
Then (H3O^+)(OH^-) = Kw = 1E-14. You know Kw and H3O^+, solve for OH^-

Answer 2

Calculate the PH of 0.025moldm3 trioxonitrate(v) solution.