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. Compounds containing alkali metals and ammonium (NH4+) cations are soluble.
  3. Compounds containing nitrates (NO3), acetates (C2H3O2), and perchlorates (ClO4) are soluble.
  4. Compounds containing chlorides (Cl) are soluble except for AgCl, PbCl2 and Hg2Cl2. Compounds containing bromides (Br) and iodides (I) have solubility similar to chlorides.
  5. Sulfate (SO42-) containing compounds are soluble except for PbSO4 and BaSO4. CaSO4 and Ag2SO4 are slightly soluble.
  6. Hydroxides (OH) are insoluble.
  7. Carbonates (CO32-), phosphates (PO43-), and arsenates (AsO43-) are insoluble.
  8. Sulfides (S2-) are insoluble.