Potassium hydrogen difluoride
3D model (Jmol)
|Molar mass||78.103 g/mol|
|Melting point||238.7 °C (461.7 °F; 511.8 K)|
|24.5 g/100 mL (0 °C)
30.1 g/100mL (10 °C)
39.2 g/100 mL (20 °C)
114.0 g/100 mL (80 °C)
|Solubility||soluble in ethanol|
|45.56 J/(mol K) |
Std enthalpy of
EU classification (DSD)
|Toxic (T), Corrosive (C)|
|Flash point||non flammable|
|Sodium bifluoride, ammonium bifluoride|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Potassium bifluoride is the inorganic compound with the formula KHF2. This colourless salt consists of the potassium cation and the bifluoride (HF2−) anion. The salt is used in etchant for glass. Sodium bifluoride is related and is also of commercial use as an etchant as well as in cleaning products.
Nature of the chemical bond in the bifluoride anion
Potassium bifluoride, as its name indicates, contains a bifluoride, or hydrogen(difluoride) anion: HF2−. This centrosymmetric triatomic anion features the strongest known hydrogen bond, with a F−H length of 114 pm, and a bond energy greater than 155 kJ mol−1.
Synthesis and reactions
The salt was prepared by Edmond Frémy who decomposed it to generate, for the first time, hydrogen fluoride. Potassium bifluoride is prepared by treating potassium carbonate or potassium hydroxide with hydrofluoric acid:
- 2 HF + KOH → KHF2 + H2O
- 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: 1940-1949. doi:10.1021/ja01174a012.
- 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
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
- Emsley, J. (1980) Very strong hydrogen bonds, Chemical Society Reviews, 9, 91-124.