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
CAS Number	7789-29-9 Y
3D model (JSmol)	Interactive image
ChemSpider	35308426 Y
ECHA InfoCard	100.029.233
EC Number	232-156-2
PubChem CID	11829350
RTECS number	TS6650000
UNII	880X05W53M Y
UN number	1811
CompTox Dashboard (EPA)	DTXSID10894159
InChI InChI=1S/F2H.K/c1-3-2;/q-1;+1 N Key: FLCWRBFUWAZYGV-UHFFFAOYSA-N N
SMILES [H-](F)F.[K+]
Properties
Chemical formula	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
Solubility in water	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
Crystal structure	monoclinic
Thermochemistry
Std molar entropy (S⦵298)	45.56 J/(mol·K) [1]
Std enthalpy of formation (ΔfH⦵298)	-417.26 kJ/(mol·K)
Hazards
GHS labelling:[2]
Pictograms
Signal word	Danger
Hazard statements	H301, H310, H314
Precautionary statements	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). N verify (what is YN ?) 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 RN 12178-06-2, m.p. 71.7 °C^[4]) 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

• Ammonium bifluoride
• Bifluoride anion

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. ISBN 3527306730.
4. Ažman, A.; Ocvirk, A.; Hadži, D.; Giguère, Paul A.; Schneider, Michel (1967-06-15). "Infrared spectra of KH₂F₃ and the structure of the H₂F₃⁻ ion". Canadian Journal of Chemistry. 45 (12). Canadian Science Publishing: 1347–1350. doi:10.1139/v67-222. ISSN 0008-4042.