What are the pH and the pOH of a saturated solution of Fe(OH) 3 ? The K sp of Fe(OH) 3 is 2.8 × 10 −39 . For a salt that has the general formula MX, an ICE chart shows that the K sp is equal to x 2 , ...What are the pH and the pOH of a saturated solution of Fe(OH) 3 ? The K sp of Fe(OH) 3 is 2.8 × 10 −39 . For a salt that has the general formula MX, an ICE chart shows that the K sp is equal to x 2 , where x is the concentration of the cation. Referring to Exercise 15, what is the appropriate formula for the K sp of a salt that has a general formula of M 2 X 3 if the concentration of the cation is defined as 2x, rather than x?