Fe3

Fe3 commonly denotes iron in the +3 oxidation state, written as Fe3+ in chemical notation. In aqueous solution, iron(III) typically forms the hexaaquairon(III) complex [Fe(H2O)6]3+, a relatively strong Lewis acid that readily hydrolyzes as pH increases to form hydroxo complexes and, ultimately, ferric hydroxide Fe(OH)3. This hydrolysis often leads to colloidal or particulate matter that can give solutions a brown coloration and cause turbidity.

Fe3+ is abundant in minerals such as hematite (Fe2O3) and goethite (FeOOH). It forms a range of complexes with ligands including fluoride, oxalate, and EDTA. The Fe3+/Fe2+ redox couple has a standard potential of about +0.77 V (in acidic solution), allowing ferric iron to be reduced to ferrous iron under appropriate conditions. In biology, ferric centers coordinate iron in proteins involved in electron transfer and catalysis, as well as in oxygen transport and storage in some systems.

Applications and implications include water treatment and environmental engineering, where ferric salts such as ferric chloride (FeCl3) and ferric sulfate are used as coagulants to remove suspended solids and color. In chemistry and catalysis, Fe3+ acts as a Lewis acid and participates in oxidation-reduction cycles with Fe2+. The ferric state also participates in reactions such as the Fenton process when cycling with hydrogen peroxide, generating reactive species.

Because of its tendency to form insoluble hydroxides, ferric iron is typically introduced to systems as salts rather than as a bare Fe3+ ion. In summary, Fe3 denotes iron in the +3 oxidation state, with ferric compounds playing key roles across geology, chemistry, environmental science, and biology.