158 CHAPTER 4: Some Types of Chemical Reactions
EXAMPLE 4-12 Solubility Guidelines and Precipitation Reactions
Will a precipitate form when aqueous solutions of Ca(NO 3 ) 2 and NaCl are mixed in reason-
able concentrations? Write balanced formula unit, total ionic, and net ionic equations for any
reaction.Plan
We recognize that both Ca(NO 3 ) 2 (solubility guideline 3) and NaCl (solubility guidelines 2
and 4) are soluble compounds. We use the solubility guidelines to determine whether any of
the possible products are insoluble.Solution
At the instant of mixing, the resulting solution contains four ions:Ca^2 (aq), NO 3 (aq), Na(aq), Cl(aq)New combinations of ions couldbe CaCl 2 and NaNO 3. But solubility guideline 4 tells us that
CaCl 2 is a soluble compound, and solubility guidelines 2 and 3 tell us that NaNO 3 is a soluble
compound. Therefore no precipitate forms in this solution.You should now work Exercise 84.EXAMPLE 4-13 Solubility Guidelines and Precipitation Reactions
Will a precipitate form when aqueous solutions of CaCl 2 and K 3 PO 4 are mixed in reasonable
concentrations? Write balanced formula unit, total ionic, and net ionic equations for any reac-
tion.Plan
We recognize that both CaCl 2 (solubility guideline 4) and K 3 PO 4 (solubility guideline 2) are
soluble compounds. We use the solubility guidelines to determine whether any of the possible
products are insoluble.Solution
At the instant of mixing, the resulting solution contains four ions:Ca^2 (aq), Cl(aq), K(aq), PO 43 (aq)New combinations of ions couldbe KCl and Ca 3 (PO 4 ) 2. Solubility guidelines 2 and 4 tell us
that KCl is a soluble compound; solubility guideline 7 tells us that Ca 3 (PO 4 ) 2 is an insoluble
compound, so a precipitate of Ca 3 (PO 4 ) 2 forms in this solution.The equations for the formation of calcium phosphate follow.3CaCl 2 (aq)2K 3 PO 4 (aq)88nCa 3 (PO 4 ) 2 (s)6KCl(aq)
3[Ca^2 (aq)2Cl(aq)]2[3K(aq)PO 43 (aq)]88n
Ca 3 (PO 4 ) 2 (s)6[K(aq)Cl(aq)]
3Ca^2 (aq)2PO 43 (aq)88nCa 3 (PO 4 ) 2 (s)You should now work Exercise 90.