Iron(II) oxide

Iron(II) oxide, also called ferrous oxide, is a chemical compound with the formula FeO. It is found in nature as a mineral called wüstite. This compound is one of several types of iron oxides and looks like a black powder. People often mistake it for rust, but rust is a different substance called hydrated iron(III) oxide.

Iron(II) oxide can also refer to a group of similar compounds that do not have exactly the same ratio of iron to oxygen. These compounds usually have a bit less iron than the simple FeO formula, with amounts ranging from Fe_0.84O to Fe_0.95O. This compound is important in many industrial processes and is used to make different products.

Occurrence

Iron(II) oxide is found in about 9% of Earth's mantle. In this layer, it might help conduct electricity, which could explain some changes in Earth's spinning.

Structure

Iron(II) oxide has a special cubic shape, similar to rock salt. In this shape, iron atoms are surrounded by oxygen atoms, and oxygen atoms are surrounded by iron atoms. Sometimes, a few iron atoms change their form, making the structure slightly different.

When melted, iron atoms are mostly surrounded by four or five oxygen atoms. At very cold temperatures, below 200 K, the structure changes slightly.

Preparation

Iron(II) oxide, or FeO, can be made by heating iron(II) oxalate. This creates FeO, carbon dioxide, and carbon monoxide. This must be done in a special environment without air to prevent a different form of iron oxide from forming.

Another way to make FeO is by heating a mix of iron and oxygen at high temperature and pressure. This method helps make the exact amount needed. The same idea can be used to make other oxides, like manganous oxide and stannous oxide.

Uses

Iron(II) oxide is used as a pigment. It is approved by the FDA for use in cosmetics and in some tattoo inks. It can also help remove phosphates from home aquariums.

Reactions

Iron(II) oxide, or FeO, is not very stable when it is below a temperature of 575 °C. At this lower temperature, it tends to break down into iron metal and another compound called Fe₃O₄. This can be shown by the equation:

4 FeO → Fe + Fe₃O₄