Question 4.5: Predicting Reaction Products Using the solubility rules in T...
Predicting Reaction Products
Using the solubility rules in Table 4.1, predict what will happen when the following pairs of solutions are mixed.
a. KN O_{3}(aq) and BaCl_{2}(aq)
b. Na_{2}SO_{4} (aq) and Pb(NO_{3})_{2}(aq)
c. KOH(aq) and Fe(NO_{3})_{3}(aq)
Table 4.1
Simple Rules for Solubility of Salts in Water
1. Most nitrate (N O_{3}^{-} ) salts are soluble.
2. Most salts of Na^{+} , K^{+} , and NH_{4}^{+} are soluble.
3. Most chloride salts are soluble. Notable exceptions are AgCl, PbCl _{2} , and Hg_{2}Cl_{2}.
4. Most sulfate salts are soluble. Notable exceptions are Ba SO_{4} , PbSO_{4} , and CaSO_{4}.
5. Most hydroxide salts are only slightly soluble. The important soluble hydroxides are NaOH, KOH, and Ca(OH) _{2} (marginally soluble).
6. Most sulfide ( S^{2-} ), carbonate ( CO_{3}^{2-} ), and phosphate ( PO_{4}^{3-} ) salts are only slightly soluble.
a. KN O_{3} (aq) stands for an aqueous solution obtained by dissolving solid KN O_{3} in water to form a solution containing the hydrated ions K^{+}(aq) and N O_{3} ^{-}(aq). Likewise, BaCl _{2} (aq) is a solution formed by dissolving solid BaCl _{2} in water to produce Ba^{2+}(aq) and Cl ^{-}(aq). When these two solutions are mixed, the resulting solution contains the ions K^{+}, N O_{3} ^{-}, Ba^{2+}, and Cl ^{-}. All will be hydrated, but (aq) is omitted for simplicity. To look for possible solid products, combine the cation from one reactant with the anion from the other:
Note from Table 4.1 that the rules predict that both KCl and Ba (NO_{3})_{2} are soluble in water. Thus no precipitate will form when KNO_{3} (aq) and BaCl _{2} (aq) are mixed. All the ions will remain dissolved in the solution. No reaction occurs.
b. Using the same procedures as in part a, we find that the ions present in the combined solution before any reaction occurs are Na^{+} , SO_{4} ^{2-}, Pb^{2+}, and N O_{3} ^{-}. The possible salts that could form precipitates are
The compound NaN O_{3} is soluble, but Pb SO_{4} is insoluble (see Rule 4 in Table 4.1). When these solutions are mixed, Pb SO_{4} will precipitate from the solution. The balanced equation is
Na_{2} SO_{4} (aq) + Pb(N O_{3})_{2} (aq) → Pb SO_{4}(s) + 2 Na_{2} N O_{3}(aq)c. The combined solution (before any reaction occurs) contains the ions K^{+} , OH^{-} , Fe^{3+}, and N O_{3} ^{-}. The salts that might precipitate are KN O_{3} and Fe(OH) _{3} . The solubility rules in Table 4.1 indicate that both K^{+} and N O_{3} ^{-} salts are soluble. However, Fe(OH) _{3} is only slightly soluble (Rule 5) and hence will precipitate. The balanced equation is
3KOH(aq) + Fe(N O_{3})_{3} (aq) → Fe(OH)_{3} (s) + 3 KN O_{3} (aq)