Potassium bifluoride
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| Names | |
|---|---|
| IUPAC name
Potassium bifluoride | |
| Other names
Potassium hydrogen difluoride | |
| Identifiers | |
7789-29-9  | |
| 3D model (Jmol) | Interactive image |
| ChemSpider | 35308426 |
| ECHA InfoCard | 100.029.233 |
| PubChem | 11829350 |
| RTECS number | TS6650000 |
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| |
| Properties | |
| HF2K | |
| 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/100mL (10 °C) 39.2 g/100 mL (20 °C) 114.0 g/100 mL (80 °C) | |
| Solubility | soluble in ethanol |
| Structure | |
| monoclinic | |
| Thermochemistry | |
| Std molar entropy (S |
45.56 J/(mol K) [1] |
| Std enthalpy of formation (ΔfH |
-417.26 kJ·K−1*mol−1 |
| Hazards | |
| EU classification (DSD) |
Toxic (T), Corrosive (C) |
| R-phrases | R25-34 |
| S-phrases | S22-26, S37-45 |
| 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 | |
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.[2]
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,[3] and a bond energy greater than 155 kJ mol−1.[4]
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
The electrolysis of KHF2 was used by Henri Moissan to isolate the element fluorine in 1886.
A related material containing two equivalents of HF is also known, KH2F3 (CAS#12178-06-2, m.p. 71.7 C). The industrial production of fluorine entails the electrolysis of molten KH2F3.[2]
See also
References
- ↑ 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.
- 1 2 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.