Influence of Weak Acids on Sparingly Soluble Phosphates

From a systematic study of the solubility of the phosphates of Ba, Sr, Cr, Zn, Mn, Co, Cu, Bi, Cd, Pb, Al, and Mg, in solutions of some organic acids, the solubility can be arranged in the ordor: oxalic> tartaric> citric> formic> aectic. The P₂O₅.solubility gradually increases with the increase in the concentration of carbonic acid in the case of Mg, Ba, Sr, Mn, Co, Cu, and Bi phosphates, but it decreases in the case of Al, Cr, Cd, Pb, and Zn phosphates. In glycinc, unlike other acids, copper phosphate instead of magnesium phosphate shows the maximum solubility. Solubility behaviour of these phosphates has been explained on the basis of pH of the equilibrium mixtures, dissociation constants, and possible reactions of the acids.