Chem Explorers

Unveiling the Allure of Ferrous Oxide: from Pigments to Polishing Agents

Introduction to Ferrous Oxide

Ferrous oxide is a black crystalline compound, widely used as a pigment and a polishing agent. The chemical formula of ferrous oxide is FeO, and it is also known as iron (II) oxide.

Ferrous oxide is commonly found in rocks, soil, and the mantle, and it is formed by the oxidation of iron at low temperatures. In this article, we will delve deeper into the chemical properties and characteristics of ferrous oxide, allowing readers to gain a comprehensive understanding of this widely used compound.

Facts about Ferrous Oxide

Ferrous oxide is a non-stoichiometric compound, meaning it does not have a fixed composition and can vary in the amount of iron and oxygen present. It has a molar mass of 71.85 g/mol and does not have a fixed structure.

Instead, it has a variable structure, depending on the method of preparation and the temperature at which it was produced. Ferrous oxide is soluble in water, producing a basic solution.

One of the most significant uses of ferrous oxide is as a pigment in the production of paints, coatings, and other materials. Due to its black color and excellent light-fastness, it is used in the production of magnetic tapes, magnetic inks, and other black pigments.

Additionally, ferrous oxide is also used as a polishing agent for optical instruments as it is not only easily dispersed but also leaves a good finish.

Chemical Properties of Ferrous Oxide


The IUPAC name of ferrous oxide is Iron(II) oxide, and it is also known as iron monoxide. It is an inorganic compound and classified as a metal oxide.

Chemical Formula

The chemical formula of ferrous oxide is FeO, indicating that it is a binary compound consisting of one iron atom and one oxygen atom. The oxidation state of the iron atom in FeO is +2.

CAS Number

Ferrous oxide has a Chemical Abstracts Service (CAS) number of 1345-25-1. The CAS number is a unique identifier for a chemical compound and is used to distinguish it from other compounds with similar names.

Chemspider ID

The ChemSpider ID of ferrous oxide is 14237. ChemSpider is a free chemical structure database that provides information on millions of chemical compounds.

Chemical Classification

Ferrous oxide is an inorganic compound and classified as a metal oxide. It is also a non-stoichiometric compound due to its variable composition.


Ferrous oxide is a widely used compound due to its properties, including solubility in water, excellent light-fastness, and black color. It is used primarily as a pigment and polishing agent in various applications, including paints, coatings, magnetic tapes, and optical instruments.

Ferrous oxide has a unique chemical formula of FeO and a CAS number of 1345-25-1. As a non-stoichiometric compound, its composition varies, making it a versatile and useful chemical compound for various industries.

Understanding the chemical properties and uses of ferrous oxide is critical in its application and manufacturing.

Physical Properties of Ferrous Oxide

Ferrous oxide is a black-colored crystalline solid with a molar density of 0.07996 mol/cm^3 or 5.745 g/cm^3. It is insoluble in water, and its melting point is 1377C (1650 K) or 2511F.

The boiling point of ferrous oxide is 3414C (3687 K) or 6177F. At room temperature, ferrous oxide is a solid.

It is a non-stoichiometric compound; thus, its stoichiometry is not fixed, and its composition may vary. Ferrous oxide’s ionic bond is the result of a difference in electronegativity between iron and oxygen ions.

Ferrous oxide exists as an ionic compound, consisting of positively charged iron cations (Fe2+) and oxygen anions (O2). The iron cation has a ionic radius of 0.630 and the oxygen anion has an ionic radius of 1.40 .

The difference in ionic radii accounts for the distortion in the crystal structure of ferrous oxide, leading to its non-stoichiometric nature.

Ionic Properties of Ferrous Oxide

In ferrous oxide, the electronic configuration of the iron cation is d^6. With a +2 oxidation state, the iron atom loses two electrons from its outermost shell to form the cation.

The oxygen anion’s electronic configuration is 2s^2 2p^4; hence, it gains two electrons to complete its octet and form the anion. The distribution of electrons leads to an ionic bond in which the electrostatic attraction between the iron cation and oxygen anion forms the ferrous oxide compound.

Ferrous oxide is classified as a basic oxide due to its alkaline or basic nature. It can react with acids to form iron salts and water.

When dissolved in water, the ferrous oxide produces a solution that has a basic pH, indicating its alkaline nature. Additionally, ferrous oxide is an ionic compound, which makes it a good electrical conductor in its molten state.

Ferrous oxide is not considered an acid-forming oxide because it cannot react with water to form an acid solution. The absence of hydrogen ions in ferrous oxide prevents it from reacting with water to form acids.

Unlike acidic oxides, which have the ability to ionize in water, ferrous oxide does not result in hydrogen ions in its aqueous solution. In conclusion, ferrous oxide is a non-stoichiometric compound with both ionic and alkaline properties.

Its black color and good light-fastness made it a favorite compound for use as a pigment in paint manufacturing. Its polishing properties also made it an essential component in the production of optical instruments.

Ferrous oxide has a unique chemical formula of FeO and is both an inorganic and non-stoichiometric compound. Understanding the physical and ionic properties of ferrous oxide is crucial in its application and in the manufacture of various materials.

Magnetic and Crystal Properties of Ferrous Oxide

Ferrous oxide exhibits paramagnetic properties due to the presence of unpaired electrons in the iron cation. Under the influence of a magnetic field, ferrous oxide experiences a magnetization, which arises from the alignment of the unpaired electrons with the field.

Ferrous oxide is characterized by a rock salt-type structure, which features a cubic lattice structure with iron atoms occupying the corners and face-centered atoms. In this structure, the iron (Fe) cations occupy the octahedral voids, which are defined as gaps between anions.

The octahedral voids enable the Fe cations to have six surrounding anion neighbors, which enhances the stability of the structure. Polarity, Conductivity, and Reactions of Ferrous Oxide

Ferrous oxide exhibits a polar covalent character, with oxygen having a higher electronegativity than iron.

The electronegativity difference between the two atoms creates a polar bond, with oxygen gaining a partial negative charge and iron having a partial positive charge. As a poor conductor of electricity, ferrous oxide does not allow the movement of charged particles through it, except in its molten state.

The absence of charged particles in its aqueous solution, makes it a poor conductor of electricity.

Ferrous oxide reacts with acids to form an iron salt and water.

The reaction of ferrous oxide with hydrochloric acid, HCl, produces iron chloride (II), FeCl2, and water (H2O). Ferrous oxide also reacts with sulfuric acid, H2SO4, producing iron sulfate (II), FeSO4, and water (H2O).

However, when nitric acid (HNO3) is used, a different reaction occurs, producing a brown oxide of nitrogen. Ferrous oxide is considered a basic metal oxide and is, therefore, unaffected by aqueous solutions of bases.

Its basic nature is apparent in the formation of an alkaline solution when dissolved in water. Ferrous oxide can undergo oxidation to form ferric oxide, commonly known as rust.

The oxidation reaction involves the gain of oxygen atoms by the iron cation, leading to the formation of Fe2O3. This reaction occurs when ferrous oxide is exposed to moisture, which initiates the reaction.

The oxidation reaction results in the formation of reddish-brown rust on the surface of the ferrous oxide, which is undesirable for most applications. Ferrous oxide undergoes disproportionation, a type of redox reaction where the same element undergoes oxidation and reduction simultaneously, in the presence of a metal.

For instance, in the reaction of ferrous oxide with aluminum in the presence of hydrochloric acid, aluminum metal displaces Fe2+(aq) ions to reduce them to elemental Fe(s), while itself oxidizing from Al(s) to AlCl3(aq). The net equation is:

3FeO(s) + 2Al(s) + 6HCl(aq) 3Fe(s) + Al2Cl6 + 3H2O(l)


Conclusion, ferrous oxide is a polar covalent compound that has limited electrical conductivity in its solid state.

When dissolved in water, ferrous oxide tends to produce a basic solution. It can react with acids to generate iron salts and water.

Moreover, it is not affected by aqueous solutions of bases. As a metal oxide, ferrous oxide can undergo both oxidation and disproportionation reactions under specific circumstances.

Understanding the polarity, conductivity, and reactions of ferrous oxide is essential in various fields and applications, including material science, chemistry, and industries that use ferrous oxide.

Hazards of Ferrous Oxide

Like any other chemical compound, ferrous oxide poses potential hazards to human health and the environment. Exposure to ferrous oxide can result in inhalation hazards, particularly if inhaled in large quantities.

The following section discusses the inhalation hazards of ferrous oxide in detail.

Inhalation Hazards

Ferrous oxide dust or powder can cause nasal and throat irritation if inhaled in large amounts. The inhalation of ferrous oxide particulates can result in acute respiratory symptoms as well as long-term health problems.

Short-term health effects may include coughing, sneezing, wheezing, and breathing difficulties. In severe cases, inhalation of ferrous oxide particulates can lead to bronchitis, pneumonia, or asthma attacks.

The inhalation hazard of ferrous oxide is primarily dependent on particle size, as smaller particles are more readily respirable and can be inhaled deep into the lungs, leading to more severe health complications. Fine particles of ferrous oxide can penetrate deeper into the respiratory system, increasing the risk of pulmonary damage and other respiratory problems.

Additionally, ferrous oxide is considered a low-toxicity substance, and there are limited studies on its effects. Due to its limited toxicity, it may not have significant health effects on the respiratory system or any other organ.

However, its effects may be more pronounced in individuals with underlying respiratory problems, children, or the elderly.

Personal Protective Equipment

To minimize the inhalation hazard of ferrous oxide, workers should wear personal protective equipment when handling and working with the compound. Protective equipment such as respirators, protective gloves, safety goggles, and protective clothing should be used when handling ferrous oxide to minimize the risk of inhalation or contact with the skin or eyes.

Furthermore, proper storage and handling of ferrous oxide can minimize the risk of inhalation hazards. Airborne dust can be minimized by storing the compound in airtight containers or sealed packaging.

Ferrous oxide should be handled in an area with good ventilation to reduce airborne concentrations of the compound.

Safe Disposal

Ferrous oxide waste should be disposed of safely and according to local and federal regulations. The compound can be recycled or repurposed for other applications or covered with soil and allowed to decompose naturally in a landfill.

It should not be disposed of in regular trash or through the sewage system. In conclusion, inhalation hazards are the primary health concern associated with the use of ferrous oxide.

While the compound is considered non-toxic, it can cause respiratory and other long-term health problems through inhalation of fine particles. Individuals exposed to ferrous oxide, especially those with respiratory problems, should seek medical attention if they experience any related symptoms.

Additionally, proper personal protective equipment and handling procedures should be followed to minimize exposure and the risk of health complications. Safe disposal of ferrous oxide waste is also crucial in minimizing the potential hazards associated with this compound.

In conclusion, ferrous oxide is a versatile compound with various properties and applications. It is used as a black pigment and a polishing agent in various industries, including paints, coatings, and optical instruments.

Understanding the chemical, physical, and ionic properties of ferrous oxide is essential for its safe and effective use. However, it is important to be aware of the potential inhalation hazards associated with the compound, which can cause nasal and throat irritation.

Proper protective measures should be taken when handling ferrous oxide to minimize these risks. Overall, by being knowledgeable and cautious, we can leverage the benefits of ferrous oxide while ensuring our safety and well-being.


1) Is ferrous oxide harmful? Ferrous oxide is considered to have limited toxicity, but inhalation of large amounts of the compound can cause nasal and throat irritation.

2) What are the main uses of ferrous oxide? Ferrous oxide is primarily used as a pigment in paints, coatings, and magnetic inks.

It is also employed as a polishing agent for optical instruments. 3) What are the hazards of inhaling ferrous oxide?

Inhalation of ferrous oxide particles can cause respiratory symptoms such as coughing, sneezing, wheezing, and breathing difficulties. It may also lead to more severe respiratory problems, especially in individuals with pre-existing conditions.

4) How can I protect myself from the inhalation hazards of ferrous oxide? Wearing personal protective equipment such as respirators, gloves, goggles, and clothing can minimize the risk of inhalation.

It is also important to handle ferrous oxide in a well-ventilated area. 5) How should ferrous oxide waste be disposed of?

Ferrous oxide waste should be disposed of according to local regulations. It can be recycled, repurposed, or disposed of in a landfill while being covered with soil.

It should not be thrown in regular trash or flushed down the drain.

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