Chromium (Cr) is a metal whose atomic number is 24 and located in group 6 in the periodic table. Its name is derived from the Greek word chroma which means color in English owing to the colored chromium containing compounds.
Abundance of Chromium in Nature: In the Earth’s crust, chromium is the 21st most abundant element. Its recorded average concentration is 100 ppm in the Earth's crust. Chromium compounds are abundant in the surrounding environment due to the erosion of chromium-containing rocks during volcanic eruptions. Chromium is also fined in (FeCr2O4) ore as chromite.
Properties and Uses of Chrome: Chrome is a brittle and hard metal possessing a lustrous appearance, a steely-grey color and a high melting point. Therefore, chrome is used in electroplating and polishing to increase resistance to tarnishing. Similar to aluminum, chrome has been also used in stainless steel industries due to its robustness. However, chromium possesses more and different oxidation states than aluminum. Chromium most abundant oxidation states are 2+, 3+ and 6+.
Chromium Salts: Although chromium III compounds are not toxic, chromium VI compounds reported high toxicity. In addition, chromium III is the most stable oxidation state. They are also characterized by possessing specific colors upon reacting with some chemicals.
Preparation of Chromium Salts: Chromium (III) salts can be obtained directly through reacting the elemental chromium with concentrated acids such as hydrochloric acid or sulfuric acid to produce chromium chloride or chromium sulfate, respectively. It can be also prepared through carbothermic chlorination of chromium oxide as shown below.
2 Cr + 6 HCl → 2 CrCl3 + 3H2
2 Cr + 3 H2SO4 → Cr2(SO4)3 + 3 H2
Cr2O3 + 3 C + 3Cl2 → 2 CrCl3 + 3 CO
In addition, it can be also produced by reducing chromium VI using cytochrome c7.
Properties and Uses of Chromium Chloride:
- Chromium chloride is a violet crystalline salt in its anhydrous form, while its color changes into dark green when it is hydrated.
- Chromium chloride is a reducing agent so it is used in organic synthesis procedures involving reduction of alkyl halides.
- Chromium chloride containing dyes have been widely used in wool staining.
- Chromium chloride has been used as a Lewis acid and catalyst in many organic reactions such as Diels Alder.
- Some studies claim that chromium (III) salts are essential in humans for insulin, sugar and lipid metabolism when used in trace amounts.
Chromium containing compounds are used in various medications such as medications for treatment of prediabetes, diabetes, as well as medications for improving athletic performance, and preventing age-related mental decline.