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Iron (II) Hydroxide: A Chemical Compound Causing Green Rust

Errah is a bookwormy and logophilic writer and science & technology teacher. He often writes about scientific ideas, theories, and research.

Chemical structure depiction of iron (II) hydroxide

Chemical structure depiction of iron (II) hydroxide


Rust is formed when iron combines with oxygen in the presence of moisture. It is usually linked with corrosion of iron-based objects such as roofs, nails, and automobiles. It has a wide range of colors, including yellow, brown, orange, and red.

Did you know that there is a type of rust that is green in color? It is caused by iron (II) hydroxide ( with some traces of oxygen). What is iron (II) hydroxide? Continue reading to learn more about it.

What Is Iron (II) Hydroxide?

Iron (II) hydroxide, also called ferrous hydroxide, is an inorganic chemical compound made up of an atom of iron in its second oxidation state (the two valence electrons of iron are linked to other ions, atoms, or molecules), and two hydroxide anions. Its chemical formula is written as Fe(OH)2. Pure iron (II) hydroxide usually exists as a white gel, powder, or trigonal crystal. When it comes into contact with oxygen in the air, it turns into a green material which is called green rust.

Iron (II) hydroxide is formed when hydroxide ions in the air interact with iron or steel surfaces. However, due to the rarity of hydroxide ions in the air, ferrous hydroxide is also uncommon in iron-based items manufactured by humans. In spite of that, it is abundant in wet environments with a lot of iron ore-bearing rocks, where water, iron, and oxygen in the air interact spontaneously over time. It can also be found in the form of varieties of minerals such as amakinite.

Iron (II) hydroxide can be synthesized in the laboratory in a variety of methods, including by reacting iron salts, such as ferrous chloride (FeCl2), with substances that contain hydroxide ions, such as lye (sodium hydroxide, NaOH). It can also be produced as a by-product of other chemical reactions. Later, we'll go through a list of reactants and reagents that can be used to make Fe(OH)2 synthetically, as well as their chemical equations.

Iron (II) hydroxide precipitates in the stream.

Iron (II) hydroxide precipitates in the stream.

Other Properties of Iron (II) Hydroxide and Potential Hazards

Iron (II) hydroxide has a density of 3.4 g/cm3 and a molecular mass of 89.86 g/mol. It has an angular or V-shaped molecular structure. It does not solute in water and many other solvents. It does not combust in the fire. When heated to 150 degrees Celsius, it breaks down into two components: iron oxide (Fe₂O₃; either II or III) and hydrogen. However, it will be a long time before its components split off. Sometimes, it can take up to two hours.

This weak base does not pose a significant threat. When a large amount of pure ferrous hydroxide comes into contact with the skin, it causes slight discomfort and, if eaten, minor stomach issues. As a matter of fact, it is used as a pigment in tattoos and as an oral medication in varying degrees of concentration.

The iron (II) hydroxide in a layered structure.

The iron (II) hydroxide in a layered structure.

Producing Synthetic Iron (II) Hydroxide

In the laboratory, you can synthetically produce iron (II) hydroxide by reacting the following reactants and reagents:

1. The reaction of iron (II) sulfate and potassium hydroxide can produce iron (II) hydroxide and potassium sulfate.

  • FeSO4 + 2 KOH → Fe (OH)2 + K2SO4
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2. The reactions of iron chloride and potassium hydroxide can produce iron (II) hydroxide and potassium chloride.

  • FeCl2 + 2 KOH → Fe (OH)2 + 2 KCl

3. You can produce iron (II) hydroxide by reacting iron, water, and oxygen.

  • 2 Fe + 2 Н2О + O2 → Fe (OH)2

4. The reaction of Iron (II) sulfate and sodium hydroxide produces iron (II) hydroxide and sodium sulfate.

  • FeSO4 + 2 NaOH →Fe (OH)2 + Na2SO4

Reaction of Iron (II) Sulfate With Sodium Hydroxide to Generate Iron (II) Hydroxide


Iron (II) hydroxide has the potential to improve the quality of water and reduce water pollution. According to research, ferrous hydroxide can remove harmful and toxic selenite and selenate ions from polluted bodies of water. When Fe(OH)2 reacts with these selenium ions, it degrades into non-dangerous elemental selenium and other harmless minerals and substances.

Other than tattoos, ferrous hydroxide is also used as pigmentation in paints, glass and cosmetic products. It can also be used in the medical field. Iron (II) hydroxide polymatose, an oral medication form of ferrous hydroxide, can be used to treat anemia and other conditions caused by the iron shortage. Moreover, iron (II) hydroxide can be used as a fertilizer in agriculture and can help plants with iron deficits. It is also used in nickel-iron batteries, wetlands decontamination, and unclogging drain and pipes.

Sources and Further Reading

  • Ferrous Hydroxide | Prezi
    This Prezi page has a slide deck with a lot of information about Fe(OH)2 that you may use in a slideshow presentation.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Errah Caunca

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