Potassium bifluoride

Potassium bifluoride is the inorganic compound with the formula K[HF2]. This colourless salt consists of the potassium cation (K+) and the bifluoride anion ([HF2]−). The salt is used as an etchant for glass. Sodium bifluoride is related and is also of commercial use as an etchant as well as in cleaning products.[3]

Potassium bifluoride
Names
IUPAC name
Potassium bifluoride
Other names
Potassium hydrogen difluoride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.233
EC Number
  • 232-156-2
RTECS number
  • TS6650000
UNII
UN number 1811
  • InChI=1S/F2H.K/c1-3-2;/q-1;+1 ☒N
    Key: FLCWRBFUWAZYGV-UHFFFAOYSA-N ☒N
  • [H-](F)F.[K+]
Properties
K[HF2]
Molar mass 78.103 g/mol
Appearance colourless solid
Odor slightly acidic
Density 2.37 g/cm3
Melting point 238.7 °C (461.7 °F; 511.8 K)
Boiling point decomposes
  • 24.5 g/(100 mL) (0 °C)
  • 30.1 g/(100 mL) (10 °C)
  • 39.2 g/(100 mL) (20 °C)
  • 114.0 g/(100 mL) (80 °C)
Solubility soluble in ethanol
Structure
monoclinic
Thermochemistry
45.56 J/(mol·K) [1]
-417.26 kJ/(mol·K)
Hazards
GHS labelling:[2]
GHS05: CorrosiveGHS06: Toxic
Danger
H301, H310, H314
P260, P262, P264, P270, P280, P301+P310, P301+P330+P331, P302+P350, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P322, P330, P361, P363, P405, P501
Flash point non flammable
Related compounds
Other anions
 Potassium fluoride
Other cations
 Sodium bifluoride, ammonium bifluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis and reactions

The salt was prepared by Edmond Frémy by treating potassium carbonate or potassium hydroxide with hydrofluoric acid:

2 HF + KOH → K[HF2] + H2O

With one more equivalent of HF, K[H2F3] (CAS#12178-06-2, m.p. 71.7 C) is produced:

HF + K[HF2] → K[H2F3]

Thermal decomposition of K[HF2] gives hydrogen fluoride:

K[HF2] → HF + KF

Applications

The industrial production of fluorine entails the electrolysis of molten K[HF2] and K[H2F3].[3] The electrolysis of K[HF2] was first used by Henri Moissan in 1886.

See also

References
  1. Westrum, Edgar F. Jr.; Pitzer, Kenneth S. (June 1949). "Thermodynamics of the System KHF2-KF-HF, Including Heat Capacities and Entropies of KHF2, and KF. The Nature of the Hydrogen Bond in KHF2". J. Am. Chem. Soc. 71 (6): 1940–1949. doi:10.1021/ja01174a012.
  2. "Potassium bifluoride". pubchem.ncbi.nlm.nih.gov. Retrieved 27 December 2021.
  3. Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307.
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