Calculate [H_{3}O^{+}] and pH in saturated Ba(OH)_{2} (aq), which contains 3.9 g Ba(OH)_{2 } ^{. } 8 H_{2}O per 100 ml solution.

What I did I first find the molarity then multiplied it to two. The I calculated the H+ using the ionization constant of water. But my answer is wrong. I calculated pH from pOH and my answer is wrong too. What is wrong with my computation?

The correct answer is 4 x 10-3 M H3O+ and pH is 12.4.

Thank you.