What must be the pH of a solution that is 0.067 M Fe3+ to just cause Fe(OH)3(s) to precipitate?
Fe(OH)3 ==> Fe^+3 + 3OH^-
Ksp = (Fe^+3)(OH^-)^3
Substitute 0.067 M for (Fe^+3) and solve for (OH^-). Then convert OH^- to pOH and subtract from 14 to obtain pH.