Hydrofluoric acid is a
solution of
hydrogen fluoride (HF) in
water. It is a precursor to almost all fluorine compounds, including pharmaceuticals such as
fluoxetine (
Prozac), diverse materials such as
PTFE (Teflon), and elemental
fluorine itself. It is a colourless solution that is highly corrosive, capable of dissolving many materials, especially
oxides. Its ability to dissolve glass has been known since the 17th century, even before
Carl Wilhelm Scheele prepared it in large quantities in 1771. Because of its high reactivity toward glass and moderate reactivity toward many metals, hydrofluoric acid is usually stored in
plastic containers (although
PTFE is slightly permeable to it).