Hydrofluoric acid (HF, CAS 7664-39-3) is a corrosive, weak, inorganic, acidic, aqueous solution of hydrogen fluoride. HF is one of the strongest inorganic acids. It is colorless, odorless, highly corrosive, and available in a range of purity grades.

Hydrofluoric acid is used in the laboratory as an intermediate in many chemical reactions and syntheses. It serves as the fluorine source for creating many organofluorine compounds, like polytetrafluoroethylene and fluoropolymers, and for high-volume inorganic fluoride compounds such as sodium aluminum hexafluoride, cryolite, and aluminum fluoride.

Other uses for hydrofluoric acid include:

• Removing and inhibiting rust
• Extracting and refining metal, rock, brick, and oil
• Producing organofluorines (fluorocarbons and refrigerants)
• Etching glass and silicone compounds

Hydrofluoric acid can dissolve glass, so it should be stored in polyethylene containers. Because it is extremely toxic and very dangerous, users must wear personal protective equipment. Unsafe exposure can cause local and systemic injuries and can be fatal.