Solubility Rules for Inorganic Compounds

These are the general solubility rules for inorganic compounds, primarily inorganic salts. Use the solubility rules to determine whether a compound will dissolve or precipitate in water.

Generally Soluble Inorganic Compounds

• Ammonium (NH₄⁺), potassium (K⁺), sodium (Na⁺) : All ammonium, potassium and sodium salts are soluble. Exceptions: some transition metal compounds.
• Bromides (Br^–), chlorides (Cl^–) and iodides (I^–): Most bromides are soluble. Exceptions: salts containing silver, lead, and mercury.
• Acetates (C₂H₃O₂^–): All acetates are soluble. Exception: silver acetate is only moderately soluble.
• Nitrates (NO₃^–): All nitrates are soluble.
• Sulfates (SO₄^2–): All sulfates are soluble except barium and lead. Silver, mercury(I), and calcium sulfates are slightly soluble. Hydrogen sulfates (HSO₄^–) (the bisulfates) are more soluble than the other sulfates.

Generally Insoluble Inorganic Compounds

• Carbonates (CO₃^2–), chromates (CrO₄^2–), phosphates (PO₄^3–), silicates (SiO₄^2–): All carbonates, chromates, phosphates, and silicates are insoluble. Exceptions: those of ammonium, potassium and sodium. An exception to the exceptions is MgCrO₄, which is soluble.
• Hydroxides (OH^–): All hydroxides (except ammonium, lithium, sodium, potassium, cesium, rubidium) are insoluble. Ba(OH)₂, Ca(OH)₂ and Sr(OH)₂ are slightly soluble.
• Silver (Ag⁺): All silver salts are insoluble. Exceptions: AgNO₃ and AgClO₄. AgC₂H₃O₂ and Ag₂SO₄ are moderately soluble.
• Sulfides (S₂^–): All sulfides (except sodium, potassium, ammonium, magnesium, calcium, and barium) are insoluble.
• Aluminum sulfides and chromium sulfides are hydrolyzed and precipitate as hydroxides.

Table of Ionic Compound Solubility in Water at 25°C

Remember, solubility depends on the temperature of the water. Compounds that don't dissolve around room temperature may become more soluble in warm water. When using the table, refer to the soluble compounds first. For example, sodium carbonate is soluble because all sodium compounds are soluble, even though most carbonates are insoluble.

As a final tip, remember solubility is not all-or-none. While some compounds completely dissolve in water and some are almost completely insoluble, many "insoluble" compounds are actually slightly soluble. If you get unexpected results in an experiment (or are looking for sources of error), remember a small amount of an insoluble compound may be participating in a chemical reaction.