Hydrogen fluoride

From Wikipedia, the free encyclopedia

Hydrogen fluoride

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)	miscible
Melting point	-84 °C (190 K, -118 ºF)
Boiling point	19.54 °C (293 K, 67.2 ºF)
NFPA 704	0 4 0
Disclaimer and references

Hydrogen fluoride is a 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. Aqueous solutions of HF, called hydrofluoric acid, are mildly acidic but strongly corrosive. HF is widely used in the petrochemical industry. It is an important component of many superacids.

1 Structure of HF
2 Uses
3 Health effects
4 References
5 External links

[edit] Structure of HF

HF forms orthorhombic crystals, consisting of zig-zag chains of HF molecules. The HF molecules, with a short H-F bond of 0.95 Å, are linked to neighboring molecules by intermolecular H--F distances of 1.55 Å.^[1]

The structure of chains of HF in crystalline hydrogen fluoride.

Liquid HF also consists of chains of HF molecules, but the chains are shorter, consisting on average of only five or six molecules.^[2] The higher boiling point of HF relative to analogous species, such as HCl, is attributed to hydrogen bonding between HF molecules, as indicated by the existence of chains even in the liquid state. HF has dipole moments.

[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^{[citation needed]} due to HF's corrosiveness and toxicity. Hydrogen fluoride is typically marketed in three common forms: anhydrous HF, aqueous 70% HF, aqueous 49% HF. HF is manufactured 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 symptoms 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 fluoride 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

^ Johnson, M. W.; Sándor, E.; Arzi, E. "The Crystal Structure of Deuterium Fluoride" Acta Crystallographica 1975, B31, pages 1998-2003. DOI: 10.1107/S0567740875006711].
^ Sylvia E. McLain, S. E.; Benmore, C. J.; Siewenie, J. E.; Urquidi, J.; Turner, J. F. C. "On the Structure of Liquid Hydrogen Fluoride" Angewandte Chemie, International Edition, 2004, volume 43, pages 1952-55. DOI: 10.1002/anie.200353289