General Solubility Rules for Ionic Compounds

• Remember these are only general rules. Exceptions do exist. (Hg₂²⁺ exceptions are not shown here because we don’t use mercury any more in our general chemistry labs.)
• You need to memorize these rules and know how to apply them.
• First of all, “soluble” means the compound will dissolve in water. “Insoluble” means it will not dissolve in water.

Always soluble:

Salts containing cations Na⁺, K⁺, NH₄⁺ and other Group IA cations.

Salts containing anions NO₃^-, CH₃CO₂^- or C₂H₃O₂^-, ClO₄^-, ClO₃^-.

Mostly soluble, with exceptions:

Salts containing halides (Cl^-, Br^-, I^-) are soluble, except for Ag⁺, Pb²⁺ salts.

Salts containing sulfates (SO₄^2-) are soluble, except for Sr²⁺, Ba²⁺, Pb²⁺ salts.

Mostly insoluble, with exceptions:

Salts containing hydroxides (OH^-) are insoluble, except Li⁺, Na⁺, K⁺, Ca²⁺, Sr²⁺, Ba²⁺ salts.

Assume to be insoluble:

All other salts may be assumed to be insoluble. This would be your best guess; however, remember there are exceptions. If experimental evidence is contrary to this rule, or if you were told otherwise, do not be surprised. You will not be held responsible for exceptions.

Note: All ionic compounds are solids to begin with. Molecular compounds, however, may be solids, liquids or gases.

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How to use the Solubility Table:

The table shown above helps you determine whether a particular compound is soluble in water (whether it will dissolve in water). You might wonder why that is something you might want to know. This is particularly important when you are dealing with precipitation reactions. If one or both of the products is/are insoluble in water, the reaction will go. If neither product is insoluble, then the reaction will not go.

For example, in the reaction where NaCl is added to AgNO₃, the products expected would be NaNO₃ and AgCl. Just because you can write a balanced equation for this does not mean the reaction will go. You need to look at the solubility of each product.

According to the solubility rules, all salts containing NO₃^- are soluble, so NaNO₃ must be soluble. The rules tell us that salts containing Cl^- are soluble except Ag⁺, Pb²⁺ salts. This means AgCl is insoluble. Our conclusion is the reaction will go, since one of the products is insoluble. AgCl is what we call a precipitate (ppt for short).

The reaction between NaCl and KNO₃, however will not go because both products (NaNO₃ and KCl) are soluble. There would be no precipitates and nothing will happen.

There is a short tutorial and drill on practicing with these solubility rules. Click here.