2- - What is the [H3O+] in a solution with [OH-] = 1 x 10-12 M?

The answer is 0.01 M

Explanation:

The problem is solved by applying the expression for ionic product of water as follows:

Kw = [H₃O⁺] [OH⁻]

Where Kw is the ionic product of water and it is 1.10⁻¹⁴ M at⁴ 25ºC. As [OH⁻] = 1.10⁻¹² M, [H₃O⁺] will be:

[H₃O⁺] = Kw / [OH⁻] = 1.10⁻¹⁴M/1.10⁻¹²M = 0.01 M