Determine the hydronium ion concentration in a solution that is 0.00018 M Ca(OH)2. Answer in units of M

1 answer

Ca(OH)2 ==> Ca^2+ + 2OH^-
If it is 0.00018M in Ca(OH)2 it must be 2*0.00018 M in OH.
Then (H3O^+)(OH^-) = Kw = 1E-14. Knowing Kw and OH^- you can calculate H3O^+