When Can Precipitates Form?
Ksp and Ion Product

Fe(OH)3 <--> Fe3+ + 3 OH-
Ksp = [Fe3+][OH-]3 = 1.6 x 10-39
I.P. = (CFe3+)(COH-)3
If I.P. >= Ksp, then the precipitate can form.

Example Problems
  1. The concentration of iron(III) is 1.00x10-5 and the hydroxide concentration is 2.00x10-3. Will a precipitate of iron(III) hydroxide form?

  2. The concentration of iron(III) is 0.0100 M. At what pH will iron(III) hydroxide form?