Ammonium bifluoride

Chembox new
Name = Ammonium hydrogen fluoride
IUPACName = Ammonium hydrogen fluoride
OtherNames = Ammonium bifluoride,ammonium hydrofluoride, ammonium acid fluoride
Section1 = Chembox Identifiers
CASNo = 1341-49-7
Section2 = Chembox Properties
Formula = [NH₄] [HF₂]
MolarMass = 57.043 g/mol
Appearance = white solid
Density = 1.5 g/cm³, solid
Solubility =
MeltingPt = 125 °C (decomposes)
BoilingPt =
Section3 = Chembox Structure
Coordination = [ammonium| [NH₄] ⁺ cation: tetrahedral
[bifluoride| [HF₂] ⁻] anion: linear
CrystalStruct = Cubic, related to the CsCl structure

Ammonium hydrogen fluoride is the inorganic compound with the formula NH₄HF₂. It is produced from ammonia and hydrogen fluoride. This colourless salt is a glass-etchant and an intermediate in a once-contemplated route to hydrofluoric acid.

tructure

In solid [NH₄] [HF₂] , each cation is surrounded by four fluorine atoms in a tetrahedron, with hydrogen - fluorine hydrogen bonds present between the hydrogen atoms of the ammonium ion and the fluorine atoms. Solutions contain tetrahedral [ammonium| [NH₄] ⁺ cations and linear [bifluoride| [HF₂] ⁻] anions.

Production and applications

Ammonium bifluoride is a compoent of some etchants. It attacks silica component of glass::SiO₂ + 4 [NH₄] [HF₂] → SiF₄ + 4 [NH₄] F + 2 H₂OPotassium bifluoride is a related more commonly used etchant.

Ammonium bifluoride has been considered as an intermediate in the production of hydrofluoric acid from hexafluorosilicic acid. Thus, hexafluorosilicic acid is hydrolyzed to give ammonium fluoride, which thermally decomposes to give the bifluoride::H₂SiF₆ + 6 NH₃ + 2 H₂ → SiO₂ + 6 NH₄F:2 NH₄F → NH₃ + [NH₄] HF₂The resulting ammonium bifluoride is converted to the sodium bifluoride, which thermally decomposes to release HF.Jean Aigueperse, Paul Mollard, Didier Devilliers, Marius Chemla, Robert Faron, Renée Romano, Jean Pierre Cuer, “Fluorine Compounds, Inorganic” in Ullmann’s Encyclopedia of Industrial Chemistry 2005 Wiley-VCH, Weinheim. DOI|10.1002/14356007.a11 307]

References

# A. F. Wells, "Structural Inorganic Chemistry", 5th ed., Oxford University Press, Oxford, UK, 1984.