Chemical property 1. Iron is an indispensable metal in the industrial sector. Iron and a small amount of carbon made of alloy - steel, magnetization is not easy to demagnetize, is an excellent hard magnetic material, but also an important industrial material, and also as the main raw material of artificial magnetic. There are many allotropes of iron. 2, iron is a more active metal, in the metal activity order table in front of hydrogen, chemical properties are more active, is a good reducing agent. Iron does not burn in air, but it burns strongly in oxygen. 3, iron is a variable valence element, 0 valence is only reductive, +6 valence is only oxidizing, +2, +3 valence both reductive and oxidizing. In the substitution reaction, there is generally a +2 valence, but a few have a +3 valence, such as iron and concentrated nitric acid reaction. At room temperature, iron is not easy to react with oxygen, sulfur, chlorine and other non-metallic elements in dry air, if there are impurities, it is easy to rust in humid air; Rust is faster in wet air in the presence of acid, base or salt solutions. At high temperatures, there is a violent reaction, such as iron burning in oxygen, Fe3O4, red hot iron and water vapor reaction also produces Fe3O4. When heated, it can be combined with halogen, sulfur, silicon, carbon, phosphorus, etc. In addition to the formation of +2 and +3 valence oxides, there is also the formation of complex oxides Fe3O4 (which is a magnetic oxide). 4, iron soluble in dilute inorganic acid, the formation of bivalent iron salt, and release hydrogen. In the case of concentrated sulfuric acid or concentrated nitric acid at room temperature, the surface of the formation of an oxide protective film, the iron "passivation", so the iron products can be loaded with cold concentrated sulfuric acid or cold concentrated nitric acid. When heated, iron can react with concentrated sulfuric acid or nitric acid to form a +3 valence iron salt, while forming SO2 or NO2.