Hydrofluoric acid (hydrofluoric acid, hydrofluoric acid, hydrofluoric acid) is an aqueous solution of hydrogen fluoride (HF). The industry is produced in the form of 40% (more often), as well as 50% and 72% of solutions. The name "hydrofluoric acid" is derived from fluorspar, from which hydrogen fluoride is obtained. It is colorless easy-moving liquid with a sharp odor and burning "vinegar" taste. Dissolution of hydrogen fluoride in water is accompanied by a rather significant heat release (59.1 kJ/mol). Hydrogen fluoride is characterized by the formation of a 38.6% HF and a boiling at 114 °C azeotropic mixture (according to other data, 37.5% and tbp 109 °C). Such an azeotrope mixture is obtained ultimately by distilling both concentrated and diluted acid.