What is the molar solubility of fe (oh) 3 in pure water? (ksp for fe (oh) 3 is 4.0 x 10-38.)

a. 6.5 x 10-7 m

b. 4.5 x 10-10 m

c. 4.0 x 10-17 m

d. 2.0 x 10-10 m

e. 3.4 x 10-13 m?

A) Pure water (assume that the pH is 7.0 and remains constant).

[OH-] = 10⁻⁷

[Fe (3+) ] = 4.0x10⁻³⁸/[OH-]³ = 4.0x10⁻¹⁷ (M)

That means the solubility is 4.0x10⁻¹⁷ mol/L.

(B) A solution buffered at pH = 5.0.

[OH-] = 10⁻⁹

[Fe (3+) ] = 4.0x10⁻³⁸/[OH-]³ = 4.0x10⁻¹¹ (M)

That means the solubility is 4.0x10⁻¹¹ mol/L.

(C) A solution buffered at pH = 11.0.

[OH-] = 10⁻³

[Fe (3+) ] = 4.0x10⁻³⁸/[OH-]³ = 4.0x10⁻²⁹ (M)

That means the solubility is 4.0x10⁻²⁹ mol/L.