Britannica Sources used in this answer

How is hydrogen fluoride different from hydrofluoric acid?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A labeled diagram of the periodic table entry for fluorine, showing its atomic number 9, symbol F, atomic weight 18.998, electron configuration, and indicating it is a halogen and a gas at room temperature. — fluorine Properties of fluorine.

The primary difference between hydrogen fluoride and hydrofluoric acid lies in their physical state and composition:

Hydrogen fluoride (HF): This is a colorless, corrosive, and fuming compound that typically exists in a gaseous state. It is produced industrially by distilling fluorspar with sulfuric acid.12
Hydrofluoric acid: This is the aqueous solution formed when hydrogen fluoride gas is dissolved in water.23

While hydrogen fluoride is the chemical compound itself, hydrofluoric acid refers specifically to its liquid solution. Industrially, hydrofluoric acid is widely utilized for cleaning metals and for etching, polishing, or frosting glass. It is important to note that hydrofluoric acid is a poisonous, weak acid that is highly reactive, particularly toward silica and silicates.23