First things first: what concentration of Ca(OH)_{2} do we need for pH of 9.2?

Since Ca(OH)

_{2} is a base, we can't use pH = -log([H

_{3}O

^{+}]), but we can use pOH = -log([OH

^{-}]), and since we know that pH + pOH = 14, we can find that for pH = 9.2 we have pOH = 4.8. Solving for hydroxide concentration, we see that [OH

^{-}] = 10

^{-4.8}, which gives us the required concentration of Ca(OH)

_{2} for pH = 9.2. Is my reasoning correct here?

We can calculate the amount of Ca(OH)

_{2} using n = m/M which yields n = 0.11 mol. Using c = n/V we can solve for V and find out the

*total* amount of water needed to have pH = 9.2. Then we simply subtract our initial volume from that number to get how much water we have to add.

Is this correct?