Solubility Rules for Inorganic Compounds

General Solubility of Inorganic Salts and Compounds

In chemistry, the solubility rules are used to determine whether a compound will dissolve in water or form a precipitate.
In chemistry, the solubility rules are used to determine whether a compound will dissolve in water or form a precipitate. Cristian Baitg / Getty Images

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 (SO42–): 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 (CO32–), chromates (CrO42–), phosphates (PO43–), silicates (SiO42–): 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 warn 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.

Soluble CompoundsExceptions (are insoluble)
Alkali metal compounds (Li+, Na+, K+, Rb+, Cs+) 
ammonium ion compounds (NH4+ 
Nitrates (NO3-), bicarbonates (HCO3-), chlorates (ClO3-) 
Halides (Cl-, Br-, I-)Halides of Ag+, Hg22+, Pb2+
Sulfates (SO42-)Sulfates of Ag+, Ca2+, Sr2+, Ba2+, Hg22+, Pb2+
Insoluble CompoundsExceptions (are soluble)
Carbonates (CO32-), phosphates (PO42-), chromates (CrO42-), sulfides (S2-)Alkali metal compounds and those containing the ammonium ion
Hydroxides (OH-)Alkali metal compounds and those containing Ba2+

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.