In what way and in what form does iron react with water?

In what way and in what form does iron react with water?

Iron does not clearly alter in pure water or in dry air, but when both water and oxygen are present (moist air), iron corrodes. Its silvery colour changes to a reddish-brown, because hydrated oxides are formed. Dissolved electrolytes accelerate the reaction mechanism, which is as follows:

4 Fe + 3 O₂ + 6 H₂O -> 4 Fe³⁺ + 12 OH^- -> 4 Fe(OH)₃ or 4 FeO(OH) + 4 H₂O

Usually the oxide layer does not protect iron from further corrosion, but is removed so more metal oxides can be formed. Electrolytes are mostly iron (II) sulphate, which forms during corrosion by atmospheric SO₂. In sea regions atmospheric salt particles may play an important role in this process.
Iron (II) hydroxide often precipitates in natural waters.

Solubility of iron and iron compounds

Elementary iron dissolves in water under normal conditions. Many iron compounds share this characteristic. Naturally occurring iron oxide, iron hydroxide, iron carbide and iron penta carbonyl are water insoluble. The water solubility of some iron compounds increases at lower pH values.
Other iron compounds may be more water soluble than the examples mentioned above. Iron carbonate has a water solubility of 60 mg/L, iron sulphide of 6 mg/L, and iron vitriol even of 295 g/L. Many iron chelation complexes are water soluble.
Usually there is a difference between water soluble Fe²⁺ compounds and generally water insoluble Fe³⁺ compounds. The latter are only water soluble in strongly acidic solutions, but water solubility increases when these are reduced to Fe²⁺ under certain conditions.