Rule 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.
Rule 2
Salts containing nitrate, acetate, chlorate, and perchlorate are soluble.
Rule 3
Salts containing Cl-, Br-, I- are soluble. Important exceptions to this rule are halide salts of Ag+, Pb2+, and Hg22+. Thus, AgCl, PbBr2, and Hg2Cl2 are all insoluble.
Rule 4
Most sulfate or sulfite salts are soluble. Important exceptions to this rule include PbSO4, Ag2SO4, HgSO4, Hg2SO4 and CaSO4, SrSO4, BaSO4.
Rule 5
Most hydroxide salts are insoluble. Ca(OH)2, Sr(OH)2, Ba(OH)2 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.
Rule 6
Most ionic compounds NOT listed above are insoluble . . . on the AP Test. Examples include: chromates, carbonates, sulfides, phosphates.
Strong Acids
HCl, HBr, HI, HNO3, HClO4, H2SO4 (for sulfuric acid, only the 1st H is strong)