[Radu]

  Hi!
  What PH does a solution get when Ag₃PO₄ is disolved into it?\
  I mean, I have found through calculations that the constant for the following reaction
    Ag₃PO₄ + 3 H₂O    3AgOH + H₃PO₄  is roughly equal to 10⁷.  So, given the very low products of solubility of silver phosphate and silver hydroxide , I can assume that the PH is acidic, due to the disolution of phosphoric acid. Any other side reaction has a constant which is significally lower than that of the above reaction.  Where am I wrong?  The PH of such a solution is basic, in fact,  and  not acidic...
      Thanks! 

[opsomath]

You are thinking along the wrong lines a bit. The important equilibrium here is

Ag₃PO₄ -> 3Ag⁺ + PO₄^-3

in other words, the solubility equilibrium of this poorly soluble silver salt. Once in solution, the phosphate is a moderately basic ion; the pKa of HPO₄^2- is about 12.3. Phosphate will deprotonate water, increasing the OH- conc. in a normal acid-base reaction.

[orgo814]

Classifying the acidity of the cation and basicity of the oxo anion would help you out.

Ag+ is clearly a non acidic cation. Use the z^2/r formula to confirm this if you are not sure what I am talking about.

Phosphate Ion is a moderately basic oxo anion. Therefore, the resulting solution will likely be basic. Given that phosphate ion is in fact basic, the oxygens on the phosphate ion will attract the hydrogens from the water molecules creating more hydroxide ions. Simple hydrolysis.