Final answer:
In an aqueous solution of Ca₃(PO₄)₂, the species present in decreasing order of concentration are Ca²⁺, PO₄³⁻, OH⁻, and H⁺. Calcium ions have the highest concentration due to the 3:2 ratio from the dissolution of calcium phosphate, followed by phosphate ions, hydroxide, and hydronium ions.
Step-by-step explanation:
To identify all chemical species present in an aqueous solution of Ca₃(PO₄)₂ and list these species in decreasing order of their concentrations, we consider the dissolution of calcium phosphate. When Ca₃(PO₄)₂ dissolves in water, it dissociates into its ions following the reaction:
Ca₃(PO₄)₂ (s) ⇒ 3Ca²⁺ (aq) + 2PO₄³⁻ (aq)
Since Ca₃(PO₄)₂ is a sparingly soluble salt, the concentration of calcium ions (Ca²⁺) will be three times the concentration of the dissolved calcium phosphate, and the concentration of phosphate ions (PO₄³⁻) will be two times this value. Moreover, because PO₄³⁻ is a weak base, it can react with water to form OH⁻ and HPO₄²⁻ in very small amounts, so H⁺ and OH⁻ ions will also be present in even lower concentrations. Hence, the species are present in the following order of decreasing concentrations: