The Lead and Iron Oxides

Here is a chemistry paper on the lead and iron oxides that I wrote in September of 2018. It provides definitions for the terms “compound” and “oxidation”, as well as giving physical and chemical descriptions of each of the three oxides of lead and the three oxides of iron. I hope you learn something, enjoy, and, if you have a question, ask in the forums!


Lead and Iron are two elements most ancient in their utilization by humans for a vast array of tools and products from swords to ceramics. Quite often, however, they were used in impure forms as oxides. Here a brief explanation of oxidation might prove useful: oxidation is an example of a chemical reaction, which is any interaction between atoms of one or more elements in specific ratios to form a new substance, called a compound (“Definition of Compound”, 2017, pp. 1). The constituents of the compound become chemically bonded and cannot be separated by physical means (“Definition of Compound”, 2017, pp. 1). The resulting compound may have entirely different properties from the constituents (Chemical Reactions, n.d.). One way to form such compounds is by oxidation, the process by which one element, the oxidizer, accepts electrons from another element thus becoming bonded to it (Clark, 2016). Oxidation was named after the gaseous element oxygen, because oxygen is an oxidizing element, as is it highly electronegative, eager to steal electrons. In fact, oxidation was originally understood as in terms of oxygen transfer, rather than the more accurate model of electron transfer (Clark, 2016). Lead and iron are both more electropositive than oxygen, so they will be oxidized in a reaction with oxygen. Depending upon the conditions in which this reaction takes place, it can lead to several different compounds with different properties and uses (Winn, 2004).

Beginning with iron, the first possible compound is a mineral called hematite. Hematite, or Fe2O3, is one of the most common minerals in the world, and is present, at least in small amounts, in many rocks, e.g. sandstone, that have a reddish or brownish coloration, caused by the presence of hematite, although the mineral itself can vary greatly in color, from gray to silver-gray, black to brown and reddish brown (Winn, 2004, pp. 1). In fact, hematite was used until recently to make a dye of the latter color, before cheaper alternatives were developed. It is also responsible for the coloration of Mars, the Red Planet (Winn, 2004, pp. 2). Although it is only paramagnetic under normal conditions, it becomes strongly magnetic when heated, similar to another iron oxide, magnetite. Its hardness ranges from 6-7 on the Mohs Scale, and it may contain small amounts of Titanium. As the principle ore of iron, hematite is mined for the industrial production of iron and is the source of approximately ninety percent of all iron. Fine mineral specimens can be found in several localities, including Minas Garais (Brazil), Cumberland (Cumbria, England), and Ria Marina (island of Elba, Italy). (Friedman, “The Mineral Hematite”, 2018). The chemical reaction that forms hematite looks like this:

4Fe+3O2→2Fe2O3 (Winn, 2004)

That is what happens if there is ample oxygen available, but a different result occurs if the oxygen is less plentiful: Fe3O4, or magnetite. Notice that magnetite has higher iron to oxygen ratio than its cousin, hematite. (Winn, 2004, pp. 4)As referenced before, magnetite earns its name for being a natural magnet and the only mineral with this property. In coloration it is dark gray to black with a hardness slightly greater than hematite at 5.5-6.5. It also differs from its duller cousin in luster, having a metallic luster. Like hematite, though less widely used, it is an important ore of iron. It is of scientific interest due its pronounced magnetic properties. Magnetite can be found almost anywhere around the world, but there are a few noteworthy sources, such as Binn Tal (Wallis, Switzerland), Parachinar (Pakistan), and Cerro Huanaquino (Potosi, Bolivia). (Friedman, “The Mineral Magnetite”, 2018). The chemical reaction that forms magnetite looks like this:

6Fe+4O2→2Fe3O4 (Winn, 2004)

The final oxide of iron is known wüstite. This compound was named after geologist and paleontologist Ewald Wüst (1875-1934) of the University of Kiel in Germany. Wüstite has a hardness of 5-5.5 and occurs mainly in meteorites and anthropogenic slags. (“Wüstite”, 2018). Although its chemical formula is often given as FeO, it breaks the law of definite proportions; the ratio of iron to oxygen ranges between 0.85-0.95/1. Because of this, it is known as a nonstoichiometric compound. This technically allows for an almost infinite number of iron oxides, but all the non-stoichiometric oxides of iron are categorized as wüstite. (Winn, 2004, pp. 9)

Despite this anomaly, most compounds do have distinct stoichiometries, like the lead oxides. first lead oxide is lead monoxide, or PbO. It forms when is heated in the presence of oxygen and can take one of two forms, litharge or massicot, differentiated by their crystal structure. Both are yellowish solids, litharge has a tetragonal crystal structure and massicot has an orthorhombic crystal structure. (“Lead”, 2018, pp. 12). They both have a hardness of 2 on the Mohs scale and have dull, greasy lusters. Litharge has a variety of uses, including in lead acid batteries, glazing pottery, pigments, lead glass, and oil refining. Litharge mines occur on every continent of the world, with an especially high concentration in European countries, such as Sweden, the United Kingdom, and Germany. (“Litharge”, 2018). Massicot mines can be found in many countries around the world, including Madagascar, Namibia, Australia, and Germany (“Massicot”, 2018).

The second lead oxide is known as minium, after the Minius river located in the Northwest of Spain. The chemical formula is Pb3O4, lead tetroxide. Another name for it is red lead, because it can be made into a beautiful read pigment that has been used in paintings since the time of the ancient Romans. Paintings made with minium are called miniatures. (“Red Lead”, n.d.). The hardness of minium is 2.5, and it has a tetragonal crystal structure just like litharge, with a similar luster. Mines are concentrated in Europe but can be found on every continent. (“Minium”, 2018).

The final oxide of lead is plattnerite, otherwise known as lead dioxide (PbO2). It was named in honor of Karl Friederich Plattner (1800-1858) who served as professor of metallurgy and assaying at the Bergakademie of Freiburg in Saxony, Germany, by Karl Wilhelm von Haidinger. It is a brown to black mineral that is commercially produced in a process involving the oxidation of the lead oxide previously discussed, minium, by chlorine (“Lead”, 2018, pp. 13). Plattnerite is used in curing polysulfide rubbers, matches and pyrotechnics, and dyes (“Lead”, 2018, pp. 13). The hardness of plattnerite is 5.5 and it has a dull, metallic luster. The plurality of plattnerite mines are in North America, and of those approximately half are in Mexico and half are in the United States, concentrated in the Western side of the country. (“Plattnerite”, 2018).

These three oxides of iron and three oxides of lead are all very useful and very different from each other. This demonstrates the power of chemical reactions, to take the same two elements in different proportions and create new substances with different properties. However, as was touched on briefly, the chemical composition of a compound is not the sole determining factor of the properties of a substance; other factors, such as crystal structure, also play very important roles, as seen in the two forms of lead monoxide, litharge and massicot (“Lead”, 2018, pp. 12). Regardless of their composition and crystal structure, human beings have used the six oxides discussed above for a long time, some for millennia (“Red Lead”, n.d.), and will probably continue utilizing these useful compounds long into the future.


References

“Chemical Reactions”. (n.d.). Retrieved September 4, 2018, from ric.edu: 

Clark, J. (2016, May 1). Definitions of Oxidation and Reduction. Retrieved September 3, 2018, from chem.lbretexts.org: 

“Definition of Compound”. (2017). Retrieved September 3, 2018, from chemicool.com: 

Friedman, H. (2018). The Mineral Hematite. Retrieved September 3, 2018, from minerals.net: 

Friedman, H. (2018). The Mineral Magnetite. Retrieved September 3, 2018, from minerals.net: 

‘Lead”. (2018). Retrieved September 3, 2018, from brittanica.com: 

“Litharge (Lead(II) Oxide), Lead Monoxide”. (2018). Retrieved September 3, 2018, from reade.com: 

“Litharge”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from mindat.org: 

“Massicot”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from mindat.org: 

“Minium”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from mindat.org: 

“Plattnerite”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from mindat.org: 

“Red Lead”. (n.d.). Retrieved September 2018, 2018, from webexibits.org:

Winn, J. S. (2004, January 6). Stoichiometry of Iron Oxides. Retrieved September 3, 2018, from dartmouth.edu: 

“Wüstite”. (2018). (Hudson Institute of Minerology) Retrieved September 3, 2018, from mindat.org: