# 5.7: Predicting Solubility Trends

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