Final answer:
At a pH of 13, the most abundant ionic species of phosphoric acid in solution is the PO4^3- ion, as the basic conditions favor complete deprotonation of the acid.
Step-by-step explanation:
The ionic species of phosphoric acid (H3PO4) that is most abundant in solution at a pH of 13 is the PO43- ion (phosphate ion). Phosphoric acid is a triprotic acid with three dissociable protons, each with its own dissociation constant (pKa). As the solution pH increases far beyond the third pKa value of 12.38, the majority of the phosphoric acid will lose all three protons to form PO43-. At pH 13, the solution is basic and the presence of OH- ions (from the water dissociation equilibrium) will shift the equilibrium of the phosphoric acid to favor the formation of the most deprotonated form, PO43-. This is reinforced by the fact that the second dissociation constant of the dihydrogen phosphate ion (H2PO4-) is much smaller compared to the hydroxyl ion concentration at pH 13, which implies that further deprotonation to HPO42- and eventually to PO43- is favored.
In a solution with a pH of 13, the most abundant ionic species of phosphoric acid (H₃PO₄) is the phosphate ion (PO₄³⁻) with a formula weight of 94 g/mol. This is because at a high pH, the concentration of hydroxide ions (OH⁻) is high, which will deprotonate each hydrogen ion from phosphoric acid until the third proton is removed, resulting in the formation of the PO₄³⁻ ion.