Physical and chemical properties of hydrofluoric acid

Physical property
Commercial usual concentration: mass fraction of solute 40%, industrial grade; Mass score 40%, electronic grade. It is a highly harmful poison. The highest density is 1.18g/cm3.
With the increase of the mass fraction of HF solution, the corrosion rate of HF on carbon steel first increases and then decreases .
Chemical property
When the concentration is low, it is weakly acidic due to the formation of hydrogen bonds, but when it is concentrated (more than 5mol/L), self-ionization will occur, and hydrofluoric acid is a very acidic acid.
Liquid hydrogen fluoride is a very acidic acid, the acidity is similar to anhydrous sulfuric acid, but weaker than fluorosulfonic acid. Strong corrosion, serious damage to teeth and bones. Highly corrosive to silicon compounds. Store in an airtight plastic bottle.
It is obtained with HF (hydrogen fluoride) dissolved in water. It is used for engraving glass, cleaning residual sand on castings, controlling fermentation, electropolishing and cleaning corroded semiconductor wafers (mixed acid with HNO3). Because hydrogen atoms and fluorine atoms have a relatively strong ability to bond, hydrofluoric acid cannot completely ionize in water.
Hydrofluoric acid can dissolve many other acids can not dissolve glass (main component: silica), the formation of gaseous silicon tetrafluoride reaction equation is as follows:
SiO2(s)+4HF(aq)=SiF4(g)↑+2H2O(l)
The resulting SiF4 can continue to interact with excess HF to produce fluorosilicic acid:
SiF4(g)+2HF(aq)=H2[SiF6](aq), fluorosilicic acid is a strong binary acid.
For this reason, it must be stored in plastic (ideally in teflon containers), wax or lead containers. Hydrofluoric acid is not reductive. If it is to be stored for a long time, not only a sealed container is needed, but the air in the container should be drained as much as possible.