Question

Calculate the molar solubility of CaO (K_sp = 1.27x10^-36) in each of the following liquids or solutions.

a) pure water

b) 0.25 M CaCl₂

c) 0.20 M Na₂O

Answer 1

a) pure water

CaO ------------> Ca^2+ (aq) + O^2-

                              S                S

Ksp = [Ca^2+][O^2-]

1.27*10^-36   = s*s

S^2                = 1.27*10^-36

S                   = 1.126*10^-18 M >>>>answer

b) 0.25 M CaCl₂

   CaO -------------> Ca^2+ + O^2-

                                S            S

                              S+0.25     S

Ksp = [Ca^2+][O^2-]

1.27*10^-36 = (s+0.25)(s)                [ S+ 0.25 = 0.25]

0.25*s            = 1.27*10^-36

   s                 = 6.35*10^-36M >>>>answer

c) 0.20 M Na₂O

CaO -------------> Ca^2+ + O^2-

                                S            S

                                S             0.2

                                               S+0.2

Ksp   = [Ca^2+][O^2-]

1.27*10^-36   = s*(s+0.2)

0.2*s              = 1.27*10^-36

   s                   =6.35*10^-36 M >>>>answer