[foollo]

What is the reaction between Fe3+ and (PO4)3-?
Would it be precipitation or ccomplex formation?

[Alberto_Kravina]

Precipitation reaction.

[woelen]

Fe(3+) and PO4(3-) form a white precipitate. It in fact also is a complex formation, the resulting compound can best be regarded as the ferric salt of a phosphato ferrate (III) complex. The formation of this complex can be nicely demonstrated by adding dilute acidified phosphate or dilute H3PO4 to a ferric salt. The liquid becomes totally colorless, which is quite surprising for an iron (III) complex. There is yet another such colorless iron (III) complex and that is FeF6(3-).

[Borek]

Quite a lot depends on pH here.

[bryanh]

Hi, I am interested in this too, would appreciate answers to any of the following.
How does Fe2+ react with phosphate?
What about Cu and Zn ions are they similar?
What is the effect, mentioned above, of pH esp. in the range 6-8?
Does the reaction require the Fe3+ to be aqueous? Fe3+ readily preciptates to hydroxides can these hydroxides react in the same way?

[Borek]

Look for Kso tables in any decent analytical chemistry textbook or handbook. These are rather complicated equilibria involving many substances so it is hard to tell what and how will react.

Below see list of species present in the solution made of 0.1M Fe³⁺ and 0.05M PO₄^3- ((s) stands for solids, numbers to the right are concentrations or for solids - amount of solid per L of solution). These are not necesarilly all species present, only those for which program I am working on already has equilibrium constants in database.