Solubility Rules
Quick reference for predicting whether common ionic compounds are soluble in water at 25 °C.
General Solubility Rules
Most nitrates (NO₃⁻) are soluble.
No common exceptions.
Most alkali metal (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and ammonium (NH₄⁺) compounds are soluble.
No common exceptions.
Most chlorides (Cl⁻), bromides (Br⁻), and iodides (I⁻) are soluble.
AgCl, PbCl₂, Hg₂Cl₂ are insoluble.
Most sulfates (SO₄²⁻) are soluble.
BaSO₄, PbSO₄, SrSO₄ are insoluble. CaSO₄ is slightly soluble.
Most hydroxides (OH⁻) are insoluble.
NaOH, KOH, Ba(OH)₂ are soluble. Ca(OH)₂ is slightly soluble.
Most sulfides (S²⁻) are insoluble.
Na₂S, K₂S, (NH₄)₂S, BaS are soluble.
Most carbonates (CO₃²⁻) and phosphates (PO₄³⁻) are insoluble.
Alkali metal and ammonium salts are soluble.
Most chromates (CrO₄²⁻) are insoluble.
Na₂CrO₄, K₂CrO₄, (NH₄)₂CrO₄ are soluble.
Quick Reference Table
| Anion | Alkali metalsNH\u2084\u207a | Alkaline earthMg\u00b2\u207a, Ca\u00b2\u207a, Sr\u00b2\u207a, Ba\u00b2\u207a | Transition metalsFe, Cu, Zn, etc. | Pb\u00b2\u207a / Ag\u207a / Hg\u2082\u00b2\u207a |
|---|---|---|---|---|
| NO₃⁻ | S | S | S | S |
| Cl⁻ / Br⁻ / I⁻ | S | S | S | I |
| SO₄²⁻ | S | SS | S | I |
| OH⁻ | S | SS | I | I |
| S²⁻ | S | S | I | I |
| CO₃²⁻ | S | I | I | I |
| PO₄³⁻ | S | I | I | I |
| CrO₄²⁻ | S | I | I | I |
This table provides general guidelines. Individual compounds may deviate — always check specific solubility data (K\u209B\u209a values) for precise work.
Related Tools & References
Solubility rules are empirical generalizations based on observations of common ionic compounds in water at approximately 25 °C. “Soluble” generally means >0.1 M, “slightly soluble” means 0.01–0.1 M, and “insoluble” means <0.01 M. For quantitative analysis, use tabulated K\u209B\u209a (solubility product) values.