![]() However, other compounds like oxide Fe 2O 3 (hematite) and iron(III) oxide-hydroxide FeO(OH) are extremely insoluble, at least at neutral pH, due to their polymeric structure. Some iron(III) salts, like the chloride FeCl 3, sulfate Fe 2(SO 4) 3, and nitrate Fe(NO 3) 3 are soluble in water. Iron(III) combines with the phosphates to form insoluble iron(III) phosphate, thus reducing the bioavailability of phosphorus - another essential element that may also be a limiting nutrient. The insolubility of iron(III) compounds can be exploited to remedy eutrophication (excessive growth of algae) in lakes contaminated by excess soluble phosphates from farm runoff. The formation of insoluble iron(III) compounds is also responsible for the low levels of iron in seawater, which is often the limiting factor for the growth of the microscopic plants ( phytoplankton) that are the basis of the marine food web. (The other plants instead encourage the growth around their roots of certain bacteria that reduce iron(III) to the more soluble iron(II).) Bacteria and grasses can thrive in such environments by secreting compounds called siderophores that form soluble complexes with iron(III), that can be reabsorbed into the cell. However, iron tends to form highly insoluble iron(III) oxides/hydroxides in aerobic ( oxygenated) environment, especially in calcareous soils. Other organisms must obtain their iron from the environment. Animals and humans can obtain the necessary iron from foods that contain it in assimilable form, such as meat. Insufficient iron in the human diet causes anemia. Nearly all living organisms, from bacteria to humans, store iron as microscopic crystals (3 to 8 nm in diameter) of iron(III) oxide hydroxide, inside a shell of the protein ferritin, from which it can be recovered as needed. Examples include oxyhemoglobin, ferredoxin, and the cytochromes. Many proteins in living beings contain bound iron(III) ions those are an important subclass of the metalloproteins. Iron(III) is usually the most stable form in air, as illustrated by the pervasiveness of rust, an insoluble iron(III)-containing material.Īlmost all known forms of life, particularly complex life, require iron. Iron is almost always encountered in the oxidation states 0 (as in the metal), +2, or +3. Iron(III) metal centres also occur in coordination complexes, such as in the anion ferrioxalate, 3−, where three bidentate oxalate ions surrounding the metal centre or, in organometallic compounds, such as the ferrocenium cation +, where two cyclopentadienyl anions are bound to the Fe III centre. The word ferric is derived from the Latin word ferrum, meaning "iron". The adjective ferrous is used instead for iron(II) salts, containing the cation Fe 2+. The adjective ferric or the prefix ferri- is often used to specify such compounds, as in ferric chloride for iron(III) chloride ( FeCl 3). In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe 3+. In chemistry, iron(III) refers to the element iron in its +3 oxidation state. ![]() The element iron in its +3 oxidation state Ferric oxide, commonly, though not precisely, called rust.
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