The hydroxide ion concentration in a saturated solution of iron(III) hydroxide, Fe(OH)3, is 2.2 10-10 M. Calculate the value for the equilibrium constant.

Question

The hydroxide ion concentration in a saturated solution of iron(III) hydroxide, Fe(OH)3, is 2.2  10-10 M. Calculate the value for the equilibrium constant.

jfraser · Answer

the dissocation equation will be$$Fe(OH){_3}(s) \rightarrow Fe^{+3}(aq) + 3OH^{-1}(aq)$$ so the equilibrium expression will be $$K_{SP} = [Fe^{+3}][OH^{-1}]^3$$ the hydroxide concentration will be 3x larger than the iron concentration. Find the iron concentration from that, plug in the values, and solve.