Illustrated Glossary of Organic Chemistry

Hydrofluoric acid: An aqueous solution of hydrogen fluoride (HF). Unlike hydrochloric acid, hydrobromic acid, and hydroiodic acid, hydrofluoric acid contains little H3O+ F-, because HF (pKa 3.2) is a weaker acid than H3O+ (pKa -1.78). Hydrofluoric acid is notorious for its ability to dissolve glass. This not because hydrofluoric acid is a strong acid, but instead because the Si-F covalent bond is among the strongest of all covalent bonds known.

Hydrofluoric acid dissolves glass, so it must be
stored a container made of plastic (such as Teflon).
Glass that has been etched by hydrofluoric acid.