The Ksp for $Fe(OH)_3$ = $2.5 x 10^-20$ . How would you find the Ksp equation in terms of $Fe^+3$ and $OH^-$ concentrations?

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Answer 1 · 2016-08-22T04:00:49

$K_(sp)=[Fe^(3+)][HO^-]^3$

We need (i) a chemical equation:

$Fe(OH)_3(s) rightleftharpoons Fe^(3+) + 3HO^-$

And (ii) a $K_(sp)$ expression:

$K_(sp)=[Fe^(3+)][HO^-]^3$

Given the normal conventions, i.e. if $S$ represents solubility etc., then,

$K_(sp)=[S][3S]^3$ $=$ $27S^4$ $=$ $2.5xx10^-20$ .

$S=""^4sqrt{(2.5xx10^-20)/(27)}$

Of course hydroxide ion or iron concentration may already be artificially high.

The Ksp for Fe(OH)_3Fe(OH)_3 = 2.5 x 10^-202.5 x 10^-20. How would you find the Ksp equation in terms of Fe^+3Fe^+3 and OH^-OH^- concentrations?