hydrogen fluoride (HF)

Hydrogen fluoride (HF) is a colorless liquid, fuming in air; a covalent hydride, preparing by distilling fluorite with concentrated sulfuric acid. Its physical properties showing typical anomalies due to hydrogen bonding. Hydrogen fluoride is a very strong acid, and an ionizing solvent for many inorganic and organic compounds; it is used to make fluorine and its compounds, especially Freon and fluorocarbons. Melting point -83°C, boiling point 20°C.

Hydrofluoric acid, a solution of hydrogen fluoride in water, is (anomalously) a weak acid, but causes very severe burns and is toxic. It dissolves silica to give fluorosilicic acid (H2SiF6), and so is used to etch glass.