Calcium phosphate, (s)

CHEMISTRY · Multi-part · AP · Chemistry · Equilibrium · Equilibrium

Problem

Calcium phosphate,

Ca_{3}(PO_{4})_{2}

(s), is an important component of bone mineral. A beaker is filled with pure water at

25\,^{\circ}\text{C}

and excess

Ca_{3}(PO_{4})_{2}

is added; the system is allowed to reach equilibrium. (a) Write the balanced chemical equation for the dissolution of

Ca_{3}(PO_{4})_{2}

(s) in water. (b) Write the equilibrium‐constant expression for

K_{sp}

that corresponds to the equation in part (a). (c) Express the ion concentrations at equilibrium in terms of a single variable

s

, where

s

represents the molar solubility of

Ca_{3}(PO_{4})_{2}

\text{mol L}^{-1}

. Derive an algebraic equation that relates

K_{sp}

s

(do not solve yet). (d) The solubility‐product constant for

Ca_{3}(PO_{4})_{2}

25\,^{\circ}\text{C}

K_{sp}=1.0\times10^{-26}

. Solve the equation from part (c) exactly for

s

and report the molar solubility in

\text{mol L}^{-1}

. (e) Explain briefly why the molar solubility of

Ca_{3}(PO_{4})_{2}

is so much smaller than that of many common ionic compounds.