Above what Fe2+ concentration will Fe(OH)2 precipitate from a buffer solution that has a pH of 8.35 ? The 𝐾sp of Fe(OH)2 is 4.87×10−17. [Fe2+]= M

Answer 1

Ksp = [Fe2+] x [OH-]²

Since the buffer solution has an alkaline pH, we can calculate the OH- concentration like this.

pH + pOH = 14 pOH = 14 - pH = 14 - 8.35 = 5.65

pOH = - log [OH-] log[OH-] = - pOH [OH-] = 10^-pOH = 10^-5.65 = 2.24 x 10^-6 moles /L

From the first equation, [Fe2+] = Ksp / [OH-]² = 4.87 x 10^-17 / (2.24 x 10^-6)²

[Fe2+] = 9.71 x 10^-6 moles / L