part1
Co(OH)2(s) ---------------> Ca^2+ (aq) + 2OH^- (aq)
                                         Â
x                Â
2x
Ksp   = [Co^2+][OH^-]^2
2.8*10^-16Â Â = x*(2x)^2
2.8*10^-16Â Â = 4x^3
x^3Â Â Â Â Â Â Â Â Â Â Â Â Â Â
= 7*10^-17
x  = 4.12*10^-6
solubility of Co(OH)2 in water = 4.12*10^-6M
part-b
Co(OH)2(s) ---------------> Ca^2+ (aq) + 2OH^- (aq)
                                         Â
x                Â
2x
Ksp   = [Co^2+][OH^-]^2
2.8*10^-16Â Â = x*(2x)^2
2.8*10^-16Â Â = 4x^3
x^3Â Â Â Â Â Â Â Â Â Â Â Â Â Â
= 7*10^-17
x  = 4.12*10^-6
[OH^-]Â Â = 2x = 2*4.12*10^-6
                      Â
= 8.24*10^-6M
POHÂ Â = -log[OH^-]
          Â
= -log8.24*10^-6
            Â
=5.084
PHÂ Â = 14-POH
         =
14-5.084
         =
8.916>>>>answer