Solubility Rules for Ionic Compounds

1. Salts containing Group I elements are soluble (Li⁺, Na⁺, K⁺, Cs⁺, Rb⁺). Exceptions to this rule are rare. Salts containing the ammonium ion (NH₄⁺) are also soluble. 
2. Salts containing nitrate ion (NO₃^-) are generally soluble. 
3. Salts containing Cl ^-, Br ^-, I ^- are generally soluble. Important exceptions to this rule are halide salts of Ag⁺, Pb²⁺, and (Hg₂)²⁺. Thus, AgCl, PbBr₂, and Hg₂Cl₂ are all insoluble. 
4. Most silver salts are insoluble. AgNO₃ and Ag(C₂H₃O₂) are common soluble salts of silver; virtually anything else is insoluble. 
5. Most sulfate salts are soluble. Important exceptions to this rule include BaSO₄, PbSO₄, Ag₂SO₄ and SrSO₄ . 
6. Most hydroxide salts are only slightly soluble. Hydroxide salts of Group I elements are soluble. Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of transition metals and Al³⁺are insoluble. Thus, Fe(OH)₃, Al(OH)₃, Co(OH)₂ are not soluble. 
7. Most sulfides of transition metals are highly insoluble. Thus, CdS, FeS, ZnS, Ag₂S are all insoluble. Arsenic, antimony, bismuth, and lead sulfides are also insoluble. 
8. Carbonates are frequently insoluble. Group II carbonates (Ca, Sr, and Ba) are insoluble. Some other insoluble carbonates include FeCO₃ and PbCO₃. 
9. Chromates are frequently insoluble. Examples: PbCrO₄, BaCrO₄ 
10. Phosphates are frequently insoluble. Examples: Ca₃(PO₄)₂, Ag₃PO₄ 
11. Fluorides are frequently insoluble. Examples: BaF₂, MgF₂ PbF₂.