You place 1.234 g of solid Ca(OH)2 in 1.00 L of pure water at 25°C and it partially dissolves. The pH of the solution is 12.40. Estimate the Ksp for Ca(OH)2.

Answer 1

Ca(OH)2 ==> Ca^2+ + 2OH^-
pH = 12.40
pOH = 14-12.40
pOH = -log(OH^-)
Ksp = (Ca^2+)(OH^-)^2.
You know (OH^-) from above, (Ca^2+) will be 1/2 of that, substitute into the Ksp expression and solve for Ksp.