Solubility Rules For Ionic Compounds In Water

Solubility Rule #1

Alkali metal ion salts and ammonium (NH₄⁺) ion salts are soluble in water.

Solubility Rule #2

Nitrate (NO₃⁻) ion salts and acetate (CH₃CO₂⁻) ion salts are soluble in water.

Solubility Rule #3

Chloride, bromide, and iodide salts are soluble except those containing Ag⁺, Hg₂²⁺, or Pb²⁺.

Solubility Rule #4

Sulfate (SO₄²⁻) salts are soluble except those of Ag⁺, Hg₂²⁺, Pb²⁺, Ca²⁺, Sr²⁺, and Ba²⁺.

Solubility Rule #5

Carbonate (CO₃²⁻), hydroxide (OH⁻), phosphate (PO₄³⁻), and sulfide (S²⁻) salts are insoluble except those of alkali metals and ammonium ions.

Alkali metal ions (group 1) examples

Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ — all soluble

Common soluble anions

NO₃⁻ and CH₃CO₂⁻ (acetate)

Common insoluble anions

CO₃²⁻, PO₄³⁻, OH⁻, and S²⁻ (except with alkali metals or NH₄⁺)

Exception to halide solubility

Ag⁺, Hg₂²⁺, Pb²⁺ form insoluble halides

Exception to sulfate solubility

Ca²⁺, Sr²⁺, Ba²⁺, Ag⁺, Hg₂²⁺, Pb²⁺ form insoluble sulfates