Chemistry Major Dire Need Help. Question about Quantative ysis Lab?

The Ksp refers to the concentration of the ions in a saturated solution, so for calcium hydroxide, Ksp = [Ca2+][OH-]^2 = 6.5e-6. You know the Ca2+ concentrationfrom the hardnes of the CaCO3, convert it to molarity of Ca2+, then solve for the [OH-], and convert it to pH.