Hydrogen fluoride (HF) is a colourless, pungent liquid or gas that is highly soluble in organic solvents and in water, in which it forms hydrofluoric acid. Calcium fluoride (CaF2) is a colourless solid that is relatively insoluble in water and dilute acids and bases. Sodium fluoride (NaF) is a colourless to white solid that is moderately soluble in water. Sulfur hexafluoride (SF6) is a colourless, odourless, inert gas that is slightly soluble in water and readily soluble in ethanol and bases.
The most common procedure used to quantify free fluoride anion is the fluoride ion-selective electrode. Microdiffusion techniques are considered to be the most accurate methods of sample preparation (i.e., liberation of free ionic fluoride from organic and inorganic complexes)."
"Hydrogen fluoride is an important industrial compound that is used mainly in the production of synthetic cryolite (Na3AlF6), aluminium fluoride (AlF3), motor gasoline alkylates and chlorofluorocarbons, with an annual world consumption in excess of 1 million tonnes. It is also used in etching semiconductor devices, cleaning and etching glass, cleaning brick and aluminium and tanning leather, as well as in commercial rust removers. Calcium fluoride is used as a flux in steel, glass and enamel production, as the raw material for the production of hydrofluoric acid and anhydrous hydrogen fluoride, and as an electrolyte in aluminium production. Sodium fluoride is used in the controlled fluoridation of drinking-water, as a preservative in glues, in glass and enamel production, as a flux in steel and aluminium production, as an insecticide and as a wood preservative. Sulfur hexafluoride is used extensively in various electronic components and in the production of magnesium and aluminium. Fluorosilicic acid (H2SiF6) and sodium hexafluorosilicate (Na2SiF6) are used for the fluoridation of drinking-water supplies.