Question

at what ph will an aqueous solution of 0.200 M ni2+ begin to precipitate as ni(oh)2 at 25 C ? the ksp of ni(oh)2 is 5.5 E-16 at 25 C

Answer 1

Ksp = 5.5 x 10^-16

Ni(OH)2 --------------------> Ni+2 + 2OH-

                                        0.200      

Ksp = [Ni+2] [OH-]^2

Ksp = (0.200) [OH-]^2

5.5 x 10^-16 = (0.200) [OH-]^2

[OH-] = 5.24 x 10^-8 M

pOH = -log [OH-]

         = -log (5.24 x 10^-8)

         = 7.28

pH + pOH = 14

pH = 6.72

pH = 6.72    Ni(OH)2 begin to precipitate