Potassium bifluoride
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]
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| Names | |
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| IUPAC name
Potassium bifluoride | |
| Other names
Potassium hydrogen difluoride | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.029.233  |
PubChem CID |
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CompTox Dashboard (EPA) |
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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⦵298) |
-417.26 kJ·K−1*mol−1 |
| Hazards | |
EU classification (DSD) (outdated) |
Toxic (T), Corrosive (C) |
| R-phrases (outdated) | R25-34 |
| S-phrases (outdated) | S22-26, S37-45 |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 | |
Synthesis and reactions
The salt was prepared by Edmond Frémy by treating potassium carbonate or potassium hydroxide with hydrofluoric acid:
- 2 HF + KOH → KHF2 + H2O
With two equivalents of HF, KH2F3 (CAS#12178-06-2, m.p. 71.7 C) is produced:
- 2 HF + KHF2 → KH2F3
Thermal decomposition of KHF2 gives hydrogen fluoride:
- KHF2 → HF + KF
Applications
The industrial production of fluorine entails the electrolysis of molten KHF2 and KH2F3.[2] The electrolysis of KHF2 was first used by Henri Moissan in 1886.
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 (6): 1940–1949. doi:10.1021/ja01174a012.
- 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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