The solubility of a substance in water is typically expressed in terms of its solubility product constant Ksp . The Ksp values represent the equilibrium constant for the dissolution of a sparingly soluble salt in water.For Calcium phosphate Ca3 PO4 2 , the dissolution reaction is:Ca3 PO4 2 s 3Ca aq + 2PO aq The Ksp value for Calcium phosphate at 25C is approximately 2.07 10.For Calcium carbonate CaCO3 , the dissolution reaction is:CaCO3 s Ca aq + CO aq The Ksp value for Calcium carbonate at 25C is approximately 3.3 10.To determine the solubility of each substance, we can use the Ksp values and the stoichiometry of the dissolution reactions. However, comparing the Ksp values directly can give us an idea of their relative solubilities.Since the Ksp value for Calcium phosphate 2.07 10 is much smaller than the Ksp value for Calcium carbonate 3.3 10 , we can conclude that Calcium phosphate is significantly less soluble in water than Calcium carbonate at standard temperature and pressure.