HF

Hydrofluoric acid is an aqueous solution of hydrogen fluoride gas. It is colorless transparent to light yellow smoke liquid. A pungent odor. Relative density 1.15 ~ 1.18. The boiling point is 112.2 degrees centigrade (38.2% by weight). Usual concentration: about 47%. Weak acid. In aqueous solution of hydrogen fluoride, the mass fraction of solute is up to 35.35%. Colorless solution; toxic. The maximum density is 1.14g/cm3, and the boiling point is 393.15K (120 DEG C). Smoke. It has weak acidity, but its ionization degree is larger than that of dilute one, but it is different from that of general weak electrolyte. Strong corrosion, serious damage to the teeth and bones. Highly corrosive to compounds of silicon. Should be kept in airtight plastic bottles. HF is soluble in water. Used to engrave glass, clean sand on casting, control fermentation, electro polishing and cleaning, corrosion of semiconductor wafers (mixed acid with HNO3). Because of the relatively strong combining ability between hydrogen atoms and fluorine atoms, hydrofluoric acid can not be completely dissociated in water.
Hydrofluoric acid can dissolve many other acid insoluble glass (silica), the reaction equation is as follows:
SiO2 (s) + 6, HF (AQ) + H2SiF6 (AQ) + 2, H2O (L)
Because of this, it must be stored in a plastic container (theoretically, in a container made of polytetrafluoroethylene). Hydrofluoric acid or a reducing agent, if stored for a long time, not only need a sealed container, and containers should be as much as possible exhaust the air.