Hard Water often contains calcium chloride. The calcium ion in solution can be detected using a solution of sodium phosphate. When a solution of calcium chloride is mixed with a solution of sodium phosphate, a precipitate forms.

Question

a. What is the chemical name for the precipitate that forms when solutions of calcium chloride and sodium phosphate are mixed?
b. Write a net ionic equation representing the reaction that occurs when solutions of calcium chloride and sodium phosphate are mixed.
c. List all spectator ions that are present when solutions of calcium chloride and sodium phosphate are mixed.

Answer 1

a. calcium phosphate
b. molecular equation:
3CaCl2 + 2Na3PO4 ==> Ca3(PO4)2 + 6NaCl
total ionic equation (with phases) aq for aqueous, s for solid:
3Ca^2(aq) + 6Cl^-(aq) + 6Na^+(aq) + 2[PO4]^3-(aq) ==> Ca3(PO4)2(s) + 6Na^+(aq) + 6Cl^-(aq)
net ionic equation:
3Ca^2(aq) + 2[PO4]^3-(aq) ==> Ca3(PO4)2(s)
c. The spectator ions are those ions in the TOTAL ionic equation above (which the problem didn't ask for) that are NOT in the net ionic equation. Those are the Na^+ and Cl^-