Question

If an aqueous solution has a hydronium ion concentration ([H3O+]) of 5.10 x 10-9 mol/L, what is the hydroxide ion concentration ([OH-]) in the solution?

Answer 1

Okay, so first you should know the value of Kw, 1.0 x 10-14. It is the auto-ionization constant for water, and Kw = [OH-] x [H3O+]

To find the [OH-], you must divide Kw by the [H3O+].

1.0 x 10-14 / 5.10 x 10-9 = 1.96 x 10-6

Therefore, [OH-] = 1.96 x 10-6

Hope this helps!