Solubility Rules

General Solubility Guidelines

1. Compounds of Group 1 elements (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and Fr⁺) or ammonium (NH₄⁺) are soluble.
2. Nitrates (NO₃^–), chlorates (ClO₃^–), perchlorates (ClO₄^–), and acetates (C₂H₃O₂^–) are soluble.
3. Chlorides (Cl^–), bromides (Br^–), and iodides (I^–) are soluble except for those of Ag⁺, Pb²⁺, and Hg₂²⁺.
4. With the exception of rule 1, most carbonates (CO₃^2–), chromates (CrO₄^2–), phosphates (PO₄^3–), and sulfites (SO₃^2–) are insoluble.
5. With the exception of rule 1 and the barium ion (Ba²⁺), hydroxides (OH^–) and sulfides (S^2–) are insoluble*.
6. With the exception of rule 2, silver (Ag⁺), mercury (Hg₂²⁺), and lead (Pb²⁺) salts are insoluble.
7. With the exceptions of compounds of calcium (Ca²⁺), strontium (Sr²⁺), barium (Ba²⁺), and the ions listed in rule 6, all sulfates are soluble.

*Calcium chromate and calcium and strontium hydroxide are classified as slightly soluble, or even soluble in some textbooks.

**Magnesium sulfide decomposes in water.

***Most of the oxides of Groups 1 and 2 react with water to form hydroxides.