Solubility Rules

Start with rule 1 and work your way down. The first rule that applies to your compound defines your compound.

1. Inorganic acids (those not containing carbon, hydrogen, and oxygen) are soluble. Low molecular mass organic acids are soluble.
2. Salts containing the alkali metal elements (Li⁺, Na⁺, K⁺, Cs⁺, Rb⁺) are soluble . There are few exceptions to this rule. Salts containing the ammonium ion (NH₄⁺) are also soluble.
3. Salts containing nitrate ion (NO₃^–) are generally soluble.
4. Salts containing Cl ^–, Br ^–, or I ^– are generally soluble. Important exceptions to this rule are halide salts of Ag⁺, Pb²⁺, and (Hg₂)²⁺.
5. Most silver salts are insoluble. AgNO₃ and AgC₂H₃O₂ are common soluble salts of silver; virtually all others are insoluble.
6. Most sulfate salts are soluble. Important exceptions to this rule include CaSO₄, BaSO₄, PbSO₄, Ag₂SO₄ and SrSO₄ .
7. Most hydroxide salts are only slightly soluble. Hydroxide salts of the alkali metals are soluble. Hydroxide salts of the alkaline earth metals (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of transition metals and aluminum are insoluble.
8. Most sulfides of transition metals are highly insoluble, including CdS, FeS, ZnS, and Ag₂S. Arsenic, antimony, bismuth, and lead sulfides are also insoluble.
9. Carbonates are frequently insoluble. Alkaline earth metal carbonates (CaCO₃, SrCO₃, and BaCO_​3) are insoluble, as are FeCO₃ and PbCO₃.
10. Chromates are frequently insoluble.
11. Phosphates such as Ca₃(PO₄)₂ and Ag₃PO₄ are frequently insoluble.
12. Fluorides such as BaF₂, MgF₂, and PbF₂ are frequently insoluble.