Hydrofluoric acid is a solution of hydrogen fluoride in water. Together with hydrogen fluoride, hydrofluoric acid is a valued source of fluorine, being the precursor to numerous pharmaceuticals, diverse polymers (e.g. Teflon), and most other synthetic materials that contain fluorine. Hydrofluoric acid is best known to the public for its ability to dissolve glass by reacting with SiO2, the major component of most glasses. This dissolution process can be described as follows:
Because of its high reactivity toward glass, hydrofluoric acid is typically stored in polyethylene or Teflon containers. It is also unique in its ability to dissolve many metal and semimetal oxides. Because of its low tendency to dissociate into H+ and F- ions in water, it is properly considered a weak acid, but it is nonetheless extremely corrosive, as explained below.