Hydrogen fluoride
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| Hydrogen fluoride | |
|---|---|
| Image:Hydrogen-fluoride-3D-vdW.png | |
| Other names | Hydrogen fluoride Fluoric acid Hydrofluoride Hydrofluoric acid Fluorine monohydride |
| Molecular formula | HF |
| Molecular Mass | 20.01 g/mol |
| Physical State | Liquid |
| CAS number | 7664-39-3 |
| Density | 0.922 kg m-3. |
| Solubility (water) | 100% by weight |
| Melting point | -84 °C (190 K, -118 ºF) |
| Boiling point | 19.54 °C (293 K, 67.2 ºF) |
| NFPA 704 | |
| Disclaimer and references | |
Hydrogen fluoride is the chemical compound with the formula HF. It is the only fluoride of hydrogen. HF boils just below room temperature whereas the other hydrogen halides condense at much lower temperatures. While this difference is commonly attributed to the strong hydrogen bonding between HF molecules, the huge discrepancy between HF and HCl, HBr, and HI is due to how the solid packs itself together[citation needed]. Hydrogen and fluoride ions are roughly the same size, and so they can pack together in a lattice form where maximum bonding can occur. This packing allows for intense interactions and thus a much higher melting point than HCl or HI. However, in HCl and HI, the halogens are so big that the close packing in the solid state can not occur, and thus different factors come into play. Namely, HI has many more electrons that can be polarized at any given moment, which allows for much better charge interactions. Therefore HF is an anomaly based solely on size and the ability to pack quite nicely in its solid form. The claim of hydrogen bonding, is valid, but not complete. Aqueous solutions of HF are mildly acidic.
Contents |
[edit] Solid state structure
[edit] Uses
HF is used for fluorinating polymers giving fluorocarbons, petroleum refining, glassmaking, aluminium manufacturing, titanium pickling, quartz purification, and metal finishing. It is also used to synthesize UF6, which is key to separating uranium isotopes.
Hydrogen fluoride can be found in consumer products for removing rust, cleaning brass, and glass etching, although use in consumer products is discouraged due to the HF's corrosiveness and toxicity. Hydrogen fluoride is typically marketed in three common forms: anhydrous HF, aqueous 70% HF, aqueous 49% HF. The manufacture of HF is accomplished by the reaction of calcium fluoride (fluorspar) and sulfuric acid:
- CaF2 + H2SO4 → CaSO4 + 2 HF
[edit] Health effects
Hydrogen fluoride is toxic and can be fatal if even small amounts are ingested or absorbed through the skin. HF burns require immediate treatment beginning with washing with water but specialized care is indicated. HF acid burns are not similar to those produced by hydrogen chloride (HCl), or other common acids. Onset time of symptoms of HF burns are proportional to concentration. Above 50% instantaneous effects are apparent. Between 20% and 50% clinical symptons may not appear for one to eight hours. Concentrations below 20% may not result in symptoms for 24 hours.
Entry routes include inhalation, ingestion, skin and eyes. Aside from burns to the eyes, skin, lungs, or digestive tract, the lowering of serum calcium (hypocalcemia) is one of the most serious consequences of HF exposure. As the free fluorine ion penetrates the skin it binds serum calcium forming covalent, nearly insoluble calcium fluoride (CaF2). This has effects on nerve conduction and can lead to extreme throbbing pain, metabolic changes, and even death.
[edit] References
- ATSDR. "ATSDR - MMG: Hydrogen Fluoride". Retrieved May 14, 2006
- Barbalace, Kenneth. "Chemical Database - Hydrogen Fluoride. EnvironmentalChemistry.com". 1995 - 2006. Retrieved May 14, 2006
- Honeywell, Industrial Fluorines G525-521, "Recommended Medical Treatment for Hydrofluoric Acid Exposure", "HF Medical Book"
- Cotton, F. A. and Wilkinson, G., "Advanced Inorganic Chemistry", John Wiley and Sons: New York, 1988.
