In this lab we have a saturated solution of calcium hydroxide, to calculate the concentration of OH-, we calculate pH of the solution initially, my first question is that is that necessary? if we have Ksp, can't we just do the ksp equation to find out the concentration without calculating the pH?

Ksp=S^2 * S and then we can get S.

do we use Hcl and titration for the calculation to be experimental and not in theory?

my second question is the second part where we calculate the solubility of Calcium hydroxide in calcium chloride solution in the same way -> Titration

let's say i use 20ml of HCl 2M , i can get the moles but in the lab instruction im given these equations:

Ca(OH)2 + 2HCl ---> Ca+2 + 2OH- + H2O

Ca(OH)+ + HCl --> Ca+ +2OH- +H2O

this second reaction that also happens according to the professor is what confused me, so let's say i get moles of HCl added, how do i figure it the concentration of hydroxide and hence the solubility of Ca(OH)2.

I'd be happy for some hints, thank you