Question 3.EP.2: Which of the following compounds would you predict are solub...
Which of the following compounds would you predict are soluble in water at room temperature? (a) KClO_{3}, (b) CaCO_{3}, (c) BaSO_{4}, (d) KMnO_{4}
Strategy
Solubility guidelines for common ions are given in Table 3.1. So we will identify the ions in each compound and consult the table as needed to determine the solubilities.
| Solubility guidelines for ionic compounds in water at room temperature | |||||
| Usually Soluble | Exceptions | ||||
| Group 1 cations (Li^{+},Na^{+},K^{+},Rb^{+},Cs^{+}), ammonium (NH_{4}^{+}) |
No common exceptions | ||||
| Nitrates (NO_{3}^{-}), nitrites (NO_{2}^{-}) | Moderately soluble: AgNO_{2} | ||||
| Chlorides, bromides, iodides (Cl^{-},Br^{-},I^{-}) |
AgCl,Hg_{2}Cl_{2},PbCl_{2},AgBr,Hg_{2}Br_{2}, PbBr_{2}, AgI, Hg_{2}I_{2}, and \ PbI_{2} |
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| Fluorides (F^{-}) | Insoluble: MgF_{2}, CaF_{2}, SrF_{2}, BaF_{2}, PbF_{2} | ||||
| Sulfates (SO_{4}^{ \ 2-}) | Insoluble: BaSO_{4}, PbSO_{4}, HgSO_{4} Moderately soluble: CaSO_{4}, SrSO_{4},Ag_{2}SO_{4} |
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| Chlorates (ClO_{3}^{-}), perchlorates (ClO_{4}^{-}) | No common exceptions | ||||
| Acetates (CH_{3}COO^{-}) | Moderately soluble: AgCH_{3}COO | ||||
| Usually Insoluble | Exceptions | ||||
| Phosphates (PO_{4}^{ \ 3-}) | Soluble: (NH_{4})_{3}PO_{4}, Na_{3}PO_{4}, K_{3}PO_{4} | ||||
| Carbonates (CO_{3}^{ \ 2-}) | Soluble: (NH_{4})_{2}CO_{3}, Na_{2}CO_{3}, K_{2}CO_{3} | ||||
| Hydroxides (OH^{-}) | Soluble: LiOH, NaOH, KOH,Ba(OH)_{2} Moderately soluble: Ca(OH)_{2}, Sr(OH)_{2} |
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| Sulfides (S^{2-}) | Soluble: (NH_{4})_{2}S, Na_{2}S, K_{2}S,MgS,CaS | ||||
(a) KClO_{3} is potassium chlorate. From the solubility guidelines in Table 3.1, we see that compounds containing K^{+} and ClO_{3}^{-} tend to be soluble and that no common exceptions are mentioned. So we predict that KClO_{3} should be soluble.
(b) CaCO_{3} is calcium carbonate. Again consulting the table, we see that carbonates are generally insoluble and that Ca^{2+} is not listed among the exceptions. Thus CaCO_{3} should be insoluble.
(c) BaSO_{4} is barium sulfate. Although most sulfates are soluble, BaSO_{4} is listed in the table as an exception to that rule. Therefore we expect BaSO_{4} to be insoluble.
(d) KMnO_{4} is potassium permanganate. Although the permanganate ion (MnO_{4}^{-}) is not listed in Table 3.1, the table does tell us that all compounds of K^{+} are soluble. So we would predict that KMnO_{4} should be soluble.
Discussion
Here we simply consulted the table to check the solubility of each compound. Chemists generally gain familiarity with many of these solubility rules and learn to recognize soluble and insoluble salts without consulting such a table. You should check with your instructor to see whether you are expected to memorize any of these rules.