J.R. S. answered 05/01/20
Ph.D. University Professor with 10+ years Tutoring Experience
Ca(OH)2(s) <===> Ca2+(aq) + 2OH-(aq)
Ksp = [Ca2+][OH-]2
Since there is a common ion present (Ca2+) provided by the added CaCl2, we know the [Ca2+] = 0.2 M
The molar solubility is given as 0.0026 M and since you get 2 OH- from each Ca(OH)2, the molar solubility of OH- will be 2 x 0.0026 M = 0.0052 M
Plugging these values into the Ksp expression, we obtain...
Ksp = [0.200][0.0052]2
Ksp = 5.4x10-6 (2 sig. figs. based on the value of 0.0026 M)