## Chemistry: The Molecular Science (5th Edition)

Acid and base used to form this ion, respectively, : $H_3PO_4$ and $Mg(OH)_2$, Complete ionic equation: $2H_3PO_4(aq) + 3Mg(OH)_2(s) -- \gt Mg_3(PO_4)_2 + 6H_2O(l)$ Net ionic equation: $2H_3PO_4(aq) + 3Mg(OH)_2(s) -- \gt Mg_3(PO_4)_2 + 6H_2O(l)$
1. Identify the ions of the salt: $(Mg_3(PO_4)_2)$: $Mg^{2+}$ and $P{O_4}^{3-}$: To the cation, add hydroxide ions: $Mg(OH)_2$; this is the base. To the anion, add hydrogen ions: $H_3PO_4$; this is the acid. 2. Now, write the balanced overall equation between them, which is: $Acid + Base -- \gt Salt + Water$ We already have the salt, so: $H_3PO_4(aq) + Mg(OH)_2(s) -- \gt Mg_3PO_4(s) + H_2O(l)$ ** According to table 3.1, magnesium hydroxide and magnesium phosphate are not soluble in water. Balance the equation: $2H_3PO_4(aq) + 3Mg(OH)_2(s) -- \gt Mg_3PO_4(s) + 6H_2O(l)$ 3. Write the complete ionic equation. - For the completely dissociated/ionized compounds, separate them by their ions: $2H_3PO_4(aq) + 3Mg(OH)_2(s) -- \gt Mg_3PO_4(s) + 6H_2O(l)$ * Phosporic acid is weak, so it is not completely dissociated in water. 4. Remove the repeated ions: $2H_3PO_4(aq) + 3Mg(OH)_2(s) -- \gt Mg_3PO_4(s) + 6H_2O(l)$ This is the net ionic equation.