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Iron(III) sulfate

physical science Maturity 11-13 Next article →

Iron(III) sulfate is a family of inorganic chemical compounds. It is also known as ferric sulfate in British English. The chemical formula for these compounds is Fe2(SO4)3(H2O)n. This formula shows that the substance can exist in many different forms. These forms are called hydrates because they contain water.

Iron(III) sulfate is important in many industrial processes. It helps make things like steel and aluminum. It is also used in the textile industry to dye fabric.

In the dyeing industry, iron(III) sulfate acts as a mordant. A mordant is a substance that helps colors stick to cloth. It is also used as a coagulant for industrial wastes. A coagulant helps particles clump together so they can be removed from water. This makes it a useful tool for cleaning up waste.

Because it is so versatile, it is produced on a very large scale.

Making these solutions is a specific chemical process. Manufacturers usually start with iron wastes. They create the solution by treating sulfuric acid with a hot solution of ferrous sulfate. To complete the reaction, they must add an oxidizing agent. An oxidizing agent is a substance that causes a chemical change in another material.

Common oxidizing agents used in this process include chlorine, nitric acid, or hydrogen peroxide. This process transforms the iron into the iron(III) state.

Scientists study the structure of these compounds using X-ray crystallography. This method allows them to see the well-defined crystalline forms of the different hydrates. When the substance is in a liquid solution, it is more complex. Scientists often assume the presence of aquo-hydroxo complexes. These include specific structures like [Fe(H2O)6]3+ and [Fe(H2O)5(OH)]2+.

Coquimbite crystal structure
Coquimbite crystal structure

These complexes involve iron ions interacting with water and hydroxide.

At a microscopic level, these ions have a very interesting electronic setup. Every ferric ion has five unpaired electrons. This specific arrangement is called a high-spin d5 electronic configuration. Because of these electrons, the ions are paramagnetic. This means they are attracted to magnetic fields. They are also considered weak chromophores, which relates to how they interact with light.

Nature produces iron sulfates, but they are usually rare minerals. Most of these minerals are not considered commercially important. One rare mineral is called mikasaite. Mikasaite is an anhydrous form, meaning it does not contain water. It is a mixed iron-aluminum sulfate with the formula (Fe3+, Al3+)2(SO4)3.

Interestingly, this mineral is connected to coal fires.

Most natural iron sulfates are hydrates rather than anhydrous minerals. Coquimbite is a nonahydrate and is likely the most common one found. There is also a rare nonahydrate called paracoquimbite. Other rare examples include kornelite, which is a heptahydrate, and quenstedtite, a decahydrate.

Coquimbite crystal structure
Coquimbite crystal structure

Some minerals, like andradite garnet, are found in Italy. These natural hydrates are often unstable. They typically form through the weathering of primary minerals like pyrite or marcasite. This weathering happens through aerobic oxidation, where the minerals react with oxygen.

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File:Coquimbite crystal structure.png
Coquimbite crystal structure.png
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