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.