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5.7: Predicting Solubility Trends

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    79775

    • The solubility of many simple ionic compounds can be predicted by applying the set of rules shown below.

    1. Salts of the alkali metal ions and the ammonium ion, Li+, Na+, K+, and NH4+ are almost always soluble.
    2. Virtually all metal nitrates and metal acetates are soluble.
    3. Metal halides are generally soluble, except for salts of Ag+, Pb2+, Cu+ and Hg+.
    4. Metal sulfates are generally soluble, except for salts of Ba2+, Pb2+ and Ca2+.
    5. With exception of the alkali metal ions and ammonium (Rule 1), the following salts are generally insoluble: metal carbonates (CO32-), metal phosphates (PO43-) and metal chromates (CrO42-).
    6. Metal hydroxides and metal sulfides are generally insoluble, except for those covered by Rule 1 and Ca2+, Sr2+ and Ba2+.

    Applying these rules to the reaction between lead nitrate and potassium iodide, the reactants are both soluble (Rule 1 and Rule 2). In the products, potassium nitrate will be soluble (Rule 2) and lead iodide will be insoluble, based on Rule 3.

    Exercise \(\PageIndex{1}\)

    Mixing each of the following salt solutions results in the formation of a precipate. In each case, identify the insoluble salt.

    1. NaCl + Pb(NO3)2
    2. Fe(C2H3O2)3 + KOH
    3. Ca(NO3)2 + K2SO4
    4. Li2S + CuSO4
    5. Co(C2H3O2)2 + LiOH

    Exercise \(\PageIndex{2}\)

    For each of the ionic compounds given below, determine whether or not the compound will be soluble in water, according to the trends given above.

    1. AgNO3              ☐ soluble                       ☐ insoluble
    2. MgCl2               ☐ soluble                       ☐ insoluble
    3. Na2SO4             ☐ soluble                       ☐ insoluble
    4. AgCl                 ☐ soluble                       ☐ insoluble
    5. Ba(NO3)2           ☐ soluble                       ☐ insoluble
    6. PbI2                  ☐ soluble                       ☐ insoluble
    7. Mg(NO3)2           ☐ soluble                      ☐ insoluble
    8. BaSO4                ☐ soluble                       ☐ insoluble
    9. FeCl3                  ☐ soluble                       ☐ insoluble
    10. Pb(CH3COO)2      ☐ soluble                       ☐ insoluble

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