4.The sulfate ion generally forms soluble salts. Insoluble Salts 1.Sulfides are usually insoluble. Oxides are usually insoluble. Exceptions include Na 2 O, K 2 O, SrO, and BaO. 3. Hydroxides are usually insoluble.
Chromates are usually insoluble.
Phosphates and carbonates are usually insoluble. The Solubility Product Expression, K sp Silver iodide is classified as an insoluble substance. Only a small amount will dissolve in water. When silver iodide is placed in water, an equilibrium is established. The amount of substance that is added to a given volume of solvent to form a saturated solution of that substance is called the solubility of the salt.