Solubility Rules for Ionic Compounds in Water

Vocabulary flashcards covering solubility rules, exceptions, and precipitate prediction strategy for ionic compounds in water.

Soluble Compounds

Ionic compounds that dissolve in water, designated with the state symbol $(aq)$.

Insoluble Compounds

Ionic compounds that do not dissolve in water and usually form a solid precipitate, designated with the state symbol $(s)$.

Precipitate

An insoluble solid compound, written with the state symbol $(s)$, that forms in water when ionic solutions are combined.

Group 1 Ions and Ammonium Rule

All salts containing Group 1 ions (such as $Li^+$, $Na^+$, $K^+$) or ammonium ($NH_4^+$) are soluble in water (e.g., $Na_2CO_3$ and $(NH_4)_2SO_4$).

Nitrate, Acetate, and Perchlorate Rule

Salts containing nitrate ($NO_3^-$), acetate ($C_2H_3O_2^-$), and perchlorate ($ClO_4^-$) are soluble in water (e.g., $AgNO_3$ and $Ca(C_2H_3O_2)_2$).

Chloride, Bromide, and Iodide Rule

Salts containing chloride ($Cl^-$), bromide ($Br^-$), and iodide ($I^-$) are usually soluble, except when combined with $Ag^+$, $Pb^{2+}$, or $Hg_2^{2+}$ (e.g., $NaCl$ is soluble, but $AgCl$ is insoluble).

Sulfate Rule

Salts containing sulfate ($SO_4^{2-}$) are usually soluble, except when combined with $Ca^{2+}$, $Sr^{2+}$, $Ba^{2+}$, $Ag^+$, or $Pb^{2+}$ (e.g., $Na_2SO_4$ is soluble, but $BaSO_4$ is insoluble).

Carbonate and Phosphate Rule

Salts containing carbonate ($CO_3^{2-}$) and phosphate ($PO_4^{3-}$) are usually insoluble, except when combined with Group 1 metal ions or $NH_4^+$ (e.g., $CaCO_3$ is insoluble, but $Na_3PO_4$ is soluble).

Hydroxide Rule

Hydroxides ($OH^-$) are usually insoluble, except for Group 1 hydroxides and $Ca(OH)_2$, $Sr(OH)_2$, and $Ba(OH)_2$ (e.g., $Fe(OH)_3$ is insoluble, but $NaOH$ is soluble).

Sulfide Rule

Sulfides ($S^{2-}$) are usually insoluble, except when combined with Group 1 metal ions, Group 2 metal ions, or $NH_4^+$ (e.g., $CuS$ is insoluble, but $Na_2S$ is soluble).

Precipitate Prediction Strategy

A procedure to predict precipitate formation by identifying constituent ions, finding the applicable solubility rule, and checking for exceptions (e.g., mixing $Na_2SO_4(aq)$ and $BaCl_2(aq)$ yields insoluble $BaSO_4(s)$ precipitate while $NaCl$ stays dissolved).