Solubility Rules for Ionic Compounds

Vocabulary flashcards covering the definitions, solubility rules, and exceptions for ionic compounds.

Soluble ionic compounds

Ionic compounds that ionize to a large extent (saturate at high concentrations) and appear to dissolve to the naked eye when a small spatula full is placed in water.

Insoluble ionic compounds

Ionic compounds that ionize very little (saturate at low concentrations) and do not appear to dissolve to the naked eye; however, a small amount still ionizes and conducts a current.

Nitrate ($NO_3^{1-}$) and acetate ($C_2H_3O_2^{1-}$) salts

Salts that are soluble in water according to solubility rules.

Alkali metal and ammonium ($NH_4^+$) salts

Salts formed with alkali metal ions ($Li^{1+}$, $Na^+$, $K^+$, $Cs^{1+}$, $Rb^{1+}$) or the ammonium ion ($NH_4^+$), all of which are soluble in water.

Halide ($F^{1-}$, $Cl^-$, $Br^-$, $I^{1-}$) salts

Salts that are mostly soluble, with notable insoluble exceptions including silver ($Ag^{1+}$), mercury(I) ($Hg_2^{2+}$), and lead(II) ($Pb^{2+}$) compounds.

Sulfate ($SO_4^{2-}$) salts

Salts that are soluble in water, except for barium ($Ba^{2+}$), lead(II) ($Pb^{2+}$), and calcium ($Ca^{2+}$) sulfates.

Hydroxide ($OH^-$) salts

Salts that are insoluble, with the exception of $Ca(OH)_2$; other alkaline earth metal hydroxides are considered insoluble but ionize to a greater extent than most insoluble salts.

Rule 6 insoluble salts

Salts containing sulfide ($S^{2-}$), carbonate ($CO_3^{2-}$), phosphate ($PO_4^{3-}$), chromate ($CrO_4^{2-}$), or dichromate ($Cr_2O_7^{2-}$), which are insoluble in water.

Solubility rule precedence

The governing guideline that dictates solubility when rules conflict: the rule nearer to the top takes precedence.