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Most of the iron in the crust is combined with various other elements to form many iron minerals. An important class is the iron oxide minerals such as hematite (Fe 2 O 3), magnetite (Fe 3 O 4), and siderite (FeCO 3), which are the major ores of iron. Many igneous rocks also contain the sulfide minerals pyrrhotite and pentlandite.
Iron(II) complexes are less stable than iron(III) complexes but the preference for O-donor ligands is less marked, so that for example [Fe(NH 3) 6] 2+ is known while [Fe(NH 3) 6] 3+ is not. They have a tendency to be oxidized to iron(III) but this can be moderated by low pH and the specific ligands used. [17]
For many substances, the formation reaction may be considered as the sum of a number of simpler reactions, either real or fictitious. The enthalpy of reaction can then be analyzed by applying Hess' law, which states that the sum of the enthalpy changes for a number of individual reaction steps equals the enthalpy change of the overall reaction.
When metallic iron (oxidation state 0) is placed in a solution of hydrochloric acid, iron(II) chloride is formed, with release of hydrogen gas, by the reaction Fe 0 + 2 H + → Fe 2+ + H 2. Iron(II) is oxidized by hydrogen peroxide to iron(III), forming a hydroxyl radical and a hydroxide ion in the process. This is the Fenton reaction.
Water-reactive substances [1] are those that spontaneously undergo a chemical reaction with water, often noted as generating flammable gas. [2] Some are highly reducing in nature. [ 3 ] Notable examples include alkali metals , lithium through caesium , and alkaline earth metals , magnesium through barium .
[10] In terms of its being an oxidant, iron(III) chloride oxidizes iron powder to form iron(II) chloride via a comproportionation reaction: [10] 2 FeCl 3 + Fe → 3 FeCl 2. A traditional synthesis of anhydrous ferrous chloride is the reduction of FeCl 3 with chlorobenzene: [25] 2 FeCl 3 + C 6 H 5 Cl → 2 FeCl 2 + C 6 H 4 Cl 2 + HCl
Structure of [Co 2 (OH 2) 10] 4+ color code: red = O, white = H, blue = Co. In the binuclear ion [Co 2 (OH 2) 10] 4+ each bridging water molecule donates one pair of electrons to one cobalt ion and another pair to the other cobalt ion. The Co-O (bridging) bond lengths are 213 picometers, and the Co-O (terminal) bond lengths are 10 pm shorter. [10]
Note that the rusting of iron is a reaction between iron and oxygen [95] that is dissolved in water, not between iron and water. Water can be oxidized to emit oxygen gas, but very few oxidants react with water even if their reduction potential is greater than the potential of O 2 /H 2 O. Almost all such reactions require a catalyst. [96]