Solubility Rules for Ionic Compounds
Ever wondered why some substances dissolve in water while others don't? These solubility rules will help you predict what happens when ionic compounds enter water (at 25°C and 1 atm pressure).
Soluble compounds include those containing Group IA ions (like Na⁺, K⁺) and ammonium (NH₄⁺) - these will always dissolve in water. Also reliably soluble are compounds with nitrate (NO₃⁻), acetate (C₂H₃O₂⁻), chlorate (ClO₃⁻), perchlorate (ClO₄⁻), and bicarbonate (HCO₃⁻) ions.
Most compounds with halide ions (Cl⁻, Br⁻, I⁻) dissolve readily, except when paired with silver (Ag⁺), lead (Pb²⁺), mercury(I) (Hg₂²⁺), or copper(I) (Cu⁺). Similarly, sulfate (SO₄²⁻) compounds are typically soluble except when combined with calcium, strontium, barium, silver, mercury(I) or lead ions.
Chemistry Tip: When two solutions are mixed and you need to predict if a precipitate forms, check if any potential compound would be insoluble according to these rules. If yes, that's your precipitate!
Insoluble compounds generally include metal hydroxides and sulfides, except those with Group IA metals, ammonium, or barium. Compounds containing carbonate (CO₃²⁻), phosphate (PO₄³⁻), sulfite (SO₃²⁻), oxide (O²⁻), chromate (CrO₄²⁻), and oxalate (C₂O₄²⁻) ions are typically insoluble as well, with Group IA and ammonium compounds as the main exceptions.