Groundwater in Pherric, New Mexico, initially contains 1.800 mg/L of iron as Fe3+. What must the pH be raised to in order to precipitate all but 0.3 mg/L of the iron? The temperature of the solution is 25 degree Celsius.

Answer 1

Fe(OH)3 ==> Fe^+3 + 3OH^-

Ksp = (Fe^+3)(OH^-)^3
Set (Fe^+3) = 0.3 mg/L converted to moles/L and solve for OH^-. Then convert OH to pOH and to pH.