Final answer:
The correct Ksp value for Ca3(PO4)2 is 2.07 × 10^-33 at 25°C, which describes the solubility equilibrium between its ions in solution and the solid compound.
Step-by-step explanation:
The correct solubility product constant (Ksp) for the equilibrium of calcium phosphate, which is represented by the formula Ca3(PO4)2, is 2.07 × 10-33 at 25°C. It defines the product of the concentrations of the calcium ions [Ca2+] and phosphate ions [PO43-] in a saturated solution where these ions are in equilibrium with solid calcium phosphate, as described by the following equilibrium expression:
Ksp = [Ca2+]3[PO43-]2
In a reaction where calcium phosphate dissolves, for every unit of Ca3(PO4)2 that dissolves, it yields three Ca2+ ions and two PO43- ions, leading to the Ksp expression shown above. Given that calcium phosphate is a sparingly soluble salt, when calculating Ksp, if the initial concentration of calcium is known (for example, 0.20 M) and assuming 'x' represents a change due to dissolution, the expression simplifies assuming 'x' is much less than the initial concentration. This is due to the low solubility of calcium phosphate. If conditions in the solution change, such as the addition of CaCl2, the solubility equilibrium will shift to maintain the Ksp value, often resulting in the precipitation of calcium phosphate.