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

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Answer 1 · 2016-08-22T04:00:49

$K_{s p} = [F e^{3 +}] {[H O^{-}]}^{3}$ $K_(sp)=[Fe^(3+)][HO^-]^3$

We need (i) a chemical equation:

$F e {(O H)}_{3} (s) ⇌ F e^{3 +} + 3 H O^{-}$ $Fe(OH)_3(s) rightleftharpoons Fe^(3+) + 3HO^-$

And (ii) a $K_{s p}$ $K_(sp)$ expression:

$K_{s p} = [F e^{3 +}] {[H O^{-}]}^{3}$ $K_(sp)=[Fe^(3+)][HO^-]^3$

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

$K_{s p} = [S] {[3 S]}^{3}$ $K_(sp)=[S][3S]^3$ $=$ $=$ $27 S^{4}$ $27S^4$ $=$ $=$ $2.5 \times 10^{- 20}$ $2.5xx10^-20$ .

$S =^{4} \sqrt{\frac{2.5 \times 10^{- 20}}{27}}$ $S=""^4sqrt{(2.5xx10^-20)/(27)}$

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

The Ksp for Fe(OH)_3Fe(OH)3Fe(OH)_3 = 2.5 x 10^-202.5x10−202.5 x 10^-20. How would you find the Ksp equation in terms of Fe^+3Fe+3Fe^+3 and OH^-OH−OH^- concentrations?