Solubility Rules

The following are some solubility rules for most common ionic solids. If two rules appear to contradict each other, apply the earlier rule.

1. Salts containing Group I elements (Li+, Na+, K+, Cs+, Rb+) and the ammonium ion (NH4+) are also soluble. 
2. Salts containing nitrate ion (NO3–) are soluble.
3. Salts containing Cl –, Br –, or I – are soluble except halide salts of Ag+, Pb2+, and (Hg2)2+  implying, AgCl, PbBr2, and Hg2Cl2 are insoluble.
4. Most silver salts are insoluble except AgNO3 and Ag(C2H3O2) which are soluble.
5. Most sulfate salts are soluble except CaSO4, BaSO4, PbSO4, Ag2SO4 and SrSO4 .
6. Most hydroxide salts are insoluble. Hydroxides of Group I elements are soluble. Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide of transition metals and Al3+ are insoluble; implying, Fe(OH)3, Al(OH)3, Co(OH)2 are not soluble.
7. Most sulfides of transition metals are highly insoluble, including CdS, FeS, ZnS, and Ag2S. Arsenic, antimony, bismuth, and lead sulfides are insoluble.
8. Carbonates are insoluble. except Na, K, and Ammonium Carbonates which are soluble. Group II carbonates (CaCO3, SrCO3, and BaCO3) are insoluble, as are FeCO3 and PbCO3.
9. Chromates are insoluble. Examples include PbCrO4 and BaCrO4.
10. Phosphates such as Ca3(PO4)2 and Ag3PO4 are insoluble.
11. Fluorides such as BaF2, MgF2, and PbF2 are insoluble.