Ca3(PO4)2 is being dissolved in water. If only 0.46 g of Ca3(PO4)2 will dissolve in 100 mL of water at 25°C, what is the solubility product, Ksp, of this salt at this temperature?

• A. 2.0 x 10^-20
• B. 3.5 x 10^-18
• C. 5.0 x 10^-15
• D. 1.0 x 10^-25

Answer: (D)

Verified step by step guidance

1. First, write the balanced dissolution equation for calcium phosphate: Ca3(PO4)2(s) ⇌ 3Ca^2+(aq) + 2PO4^3-(aq).
2. Calculate the molar mass of Ca3(PO4)2 by adding the atomic masses of all atoms in the formula: Ca (40.08 g/mol), P (30.97 g/mol), and O (16.00 g/mol).
3. Determine the number of moles of Ca3(PO4)2 that dissolve in 100 mL of water by dividing the mass of the dissolved salt (0.46 g) by its molar mass.
4. Use the stoichiometry of the dissolution reaction to find the concentrations of Ca^2+ and PO4^3- ions in the solution. For every mole of Ca3(PO4)2 that dissolves, 3 moles of Ca^2+ and 2 moles of PO4^3- are produced.
5. Calculate the solubility product, Ksp, using the expression Ksp = [Ca^2+]^3[PO4^3-]^2, substituting the concentrations of the ions obtained from the previous step.