Fluorine was isolated for the first time as a pure element in 1886 by H. Moissan, who carried out the electrolysis of potassium fluoride solutions in anhydrous hydrofluoric acid. It is a relatively abundant element in nature where, given its high reactivity, it is not in the free but combined state and constitutes about 0.03% by weight of the earth’s crust. It is found essentially in the following minerals: fluorite (CaF2), cryolite (Na3AlF6) and apatite.
As a free element it is a pale yellow gas with a pungent odor. Because of its high electronegativity, it reacts with almost all metals, with most inorganic and organic compounds, and forms compounds with all elements except noble gases. In particular, even at low temperatures, it reacts explosively with hydrogen used in the Fluorochemical Industry.
It reacts violently by combining with water hydrogen and developing oxygen. In the human body, fluorine is present in the hard tissues of the tooth and is particularly important in the prevention of dental caries. For this reason, some of its salts (sodium fluoride, tin fluoride) are usually added to toothpaste.
Some fluorides on the other hand can carry out dangerous toxic actions: they can inhibit the activity of numerous enzymes, block cellular respiration, exert anticoagulant effects and, if taken in fair quantities, can produce serious alterations to the bone structure.
Fluorine used in the Fluorochemical Industry generally forms ionic-type compounds with metals and covalent with non-metals, in which it has the oxidation number -1. Hydrogen fluoride HF (hydrofluoric acid if in aqueous solution), is a liquid that evaporates easily, colorless and irritating, which smokes in the air.
It is miscible with water in all proportions and forms an azeotrope with it; unlike HCl, in aqueous solution the HF behaves as a relatively weak acid, of a strength comparable to that of formic acid.
Both in the anhydrous state and in the aqueous solution the hydrogen fluoride has the characteristic property of reacting with silica and silicates, and is therefore able to attack glass, porcelain and similar materials. In the anhydrous state it does not cold attack metals, so that it can be stored in steel containers, but it easily reacts with oxides or halides thereof. It is produced from fluorite, which is purified by flotation and then treated with 98% sulfuric acid at a temperature of about 250 ° C:
AlF3 aluminum fluoride, a white solid used as an electrolyte in aluminum refining. Calcium fluoride CaF2, is the fluorite mineral, from which fluorine is derived. Potassium fluoride KHF2, white solid, soluble in water, used as an electrolyte in fluorine production.