Which Phosphate Species Will Precipitate Out First?

Explanation:

The precipitation of a phosphate species will occur when the solubility product (Q) of the phosphate species exceeds the solubility product constant (Ksp) for the given solid. In this case, the phosphate species present in the solution are PO4^3−, HPO4^2−, and H2PO4^−. To determine which species will precipitate first, we need to compare the Q values of each species to their respective Ksp values. The phosphate species with the smallest Q/Ksp ratio will precipitate first.

The Ksp value for Ca3(PO4)2 is 2.07 × 10^-33. If we add solid Na3PO4 to the solution, it will react with Ca2+ to form Ca3(PO4)2, so the Q value for PO4^3− will increase. However, the Q values for HPO4^2− and H2PO4^− will not change significantly.

Therefore, the phosphate species that will precipitate out of solution first is A) PO4^3−.