About 13% of the acid in a 0.10M solution of a weak acid dissociates to form ions.

What is the H3O+ concentration?
What is the OH- concentration?
What is the pH of the solution?

1 answer

If the acid is 0.1M and it dissociates 0.13 fraction then 0.1 x 0.13 = 0.013 = (H3O^+)
pH = -log(H3O^+)
pH + pOH = pKw = 14. You have pH and pKw, solve for pOH.