- #1

Revengeance

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## Homework Statement

If 0.025 g of Fe(OH)3 is added to 3.84 L of water, what mass will dissolve? Ksp is 2.8E-39.

## Homework Equations

Ksp = [x][x]

n= m/M

## The Attempt at a Solution

I believe in this question that the starting mass is deemed irrelevant (although now i am starting to believe that is required to do something)

So, Fe(OH)3 = Fe + 3OH, this means that our Ksp equation will be

(x)(3x)^3 = 2.8E-39

So we can simplify to 27x^4 = 2.8E-39, solve for x to get the concentration, which will yield 1.009E-10 mol/L.Now multiply by volume:

1.009E-10 mol/L * 3.84 L = 3.875E-10 mol * 106.8670 g/mol = 4.14E-8 grams. This is what i am getting and this incorrect. Can someone explain why, and also can someone explain if we have to use the starting mass somehow.