Hydrofluoric acid
297117
224731319
2008-07-10T04:30:07Z
203.162.41.201
/* External links */
{{Chembox new
| ImageFile = Hydrogen fluoride.svg
| ImageSize = 100px
| ImageName = Hydrofluoric acid
| ImageFile1 = Hydrogen-fluoride-3D-vdW.png
| ImageSize1 = 100px
| ImageName1 = Hydrogen fluoride molecule
| OtherNames = fluoric acid; fluorhydric acid
| Section1 = {{Chembox Identifiers
| CASNo = 7664-39-3
| RTECS = MW7875000
}}
| Section2 = {{Chembox Properties
| Formula = [[Hydrogen|H]][[Flourine|F]]
| MolarMass = not applicable<br /> (see [[hydrogen fluoride]])
| Appearance = Colorless solution
| Density = 1.15 g/mL (for 48% soln.)
| Solubility = [[Miscible]].
| MeltingPt = not applicable<br /> (see [[hydrogen fluoride]])
| BoilingPt = not applicable<br /> (see [[hydrogen fluoride]])
| pKa = 3.15 (in [[water]])
}}
| Section7 = {{Chembox Hazards
| MainHazards = Very Toxic, Corrosive.
| NFPA-H = 4
| NFPA-R = 1
| FlashPt = nonflammable
| RPhrases = {{R26/27/28}}, {{R35}}
| SPhrases = {{S1/2}}, {{S7/9}}, {{S26}}, {{S36/37}}, {{S45}}
}}
| Section8 = {{Chembox Related
| OtherAnions = [[Hydrochloric acid]]<br />[[Hydrobromic acid]]<br />[[Hydroiodic acid]]
| OtherCpds = [[Hydrogen fluoride]]<br /> [[fluorosilicic acid]]
}}
}}
'''Hydrofluoric acid''' is a [[solution]] of [[hydrogen fluoride]] in [[water]]. Together with hydrogen fluoride, hydrofluoric acid is a valued source of fluorine, being the precursor to numerous pharmaceuticals, diverse polymers (e.g. [[Polytetrafluoroethylene|Teflon]]), and most other synthetic materials that contain fluorine. Hydrofluoric acid is best known to the public for its ability to dissolve [[glass]] by reacting with SiO<sub>2</sub>, the major component of most glasses. This dissolution process can be described as follows:
:[[silicon dioxide|SiO<sub>2(s)</sub>]] + 4HF<sub>(aq)</sub> → [[silicon tetrafluoride|SiF<sub>4</sub><sub>(g)</sub>]] + 2[[water|H<sub>2</sub>O<sub>(l)</sub>]]
:SiO<sub>2(s)</sub> + 6HF<sub>(aq)</sub> → [[dihydrogen hexafluorosilicate|H<sub>2</sub>[SiF<sub>6</sub>]<sub>(aq)</sub>]] + 2H<sub>2</sub>O<sub>(l)</sub>
Because of its high reactivity toward glass, hydrofluoric acid is typically stored in [[polyethylene]] or [[polytetrafluoroethylene|Teflon]] containers. It is also unique in its ability to dissolve many [[metal]] and [[semimetal]] [[oxide]]s. It is [[corrosive]], as explained below.
==Acidity==
Hydrogen fluoride ionizes in aqueous solution in a similar fashion to other common acids:
:HF + H<sub>2</sub>O → H<sub>3</sub>O<sup>+</sup> + F<sup>−</sup>
When the concentration of HF approaches 100%, the acidity increases dramatically due to the following equilibrium:
:2HF → H<sup>+</sup> + [[hydrogen difluoride|FHF]]<sup>−</sup>
The FHF<sup>−</sup> anion is stabilized by the very strong hydrogen - fluorine [[hydrogen bond]]. Hydrofluoric acid is the only one of the hydrohalic acids that is not considered a strong acid due to its lack of ionization in aqueous solution.
==Production==
{{main|hydrogen fluoride}}
Industrially, hydrofluoric acid is produced by treatment of the mineral [[fluorite]] (CaF<sub>2</sub>) with concentrated [[sulfuric acid]]. When combined at 250 °C, these two substances react to produce hydrogen fluoride according to the following [[chemical equation]]:
:CaF<sub>2</sub> + H<sub>2</sub>SO<sub>4</sub> → 2HF + [[Calcium sulfate|CaSO<sub>4</sub>]]
==Uses==
Because of its ability to dissolve metal oxides, hydrofluoric acid is used in the purification of both [[aluminium]] and [[uranium]]. It is also used to etch [[glass]], to remove surface oxides from [[silicon]] in the [[semiconductor]] industry, as a catalyst for the alkylation of [[isobutane]] and [[butene]] (olefinic C4) in [[oil refineries]], and to remove oxide impurities from [[stainless steel]] in a process called ''pickling''. Dilute hydrofluoric acid is sold as a household rust stain remover. Recently it has even been used in [[car wash]]es in "wheel cleaner" compounds.<ref>{{cite journal | last = Strachan | first = John | title = A deadly rinse: The dangers of hydrofluoric acid | journal = Professional Carwashing & Detailing | date= January, 1999 | url = http://www.carwash.com/article.asp?IndexID=4230101 | accessdate = 2006-08-30 }}</ref> Due to its ability to dissolve silicate compounds, hydrofluoric acid is often used to dissolve rock samples (usually powdered) prior to analysis.
Hydrofluoric acid is also used in the synthesis of many [[fluorine]]-containing organic compounds, including [[Polytetrafluoroethylene|Teflon]], [[fluoropolymer]]s, [[perfluorocarbon]]s, and [[refrigeration|refrigerants]] such as [[freon]]. Additionally, hydrofluoric acid is commonly used in [[refinery]] [[alkylation]] processes to produce a high-octane gasoline blending component called [[alkylate]] from [[FCCU]] C3 and C4 [[olefins]] and [[isobutane]].
Diluted hydrofluoric acid (1 to 3 %wt.) is used in the [[petroleum industry]] in a mixture with other acids (HCl or organic acids) in order to stimulate the production of water, oil and gas wells.
==Affinity for magnesium and calcium==
Hydrofluoric acid attacks many metal oxides, forming the corresponding fluoro derivatives. In the body, hydrofluoric acid reacts with the ubiquitous biologically important [[ion]]s [[calcium|Ca<sup>2+</sup>]] and [[magnesium|Mg<sup>2+</sup>]]. In some cases, exposures can lead to [[hypocalcemia]]. Thus, hydrofluoric acid exposure is often treated with [[calcium gluconate]], a source of Ca<sup>2+</sup> that sequesters the fluoride ions.
==Safety==
[[Image:Skull and crossbones.svg|left|80px|thumb]]
[[Image:Dangclass8.png|left|80px|thumb]]
Hydrofluoric acid is [[corrosive]] and a contact [[poison]]. It should be handled with extreme care, beyond that accorded to other mineral acids, in part because of its low [[dissociation constant]], which allows HF to penetrate tissue more quickly. Symptoms of exposure to hydrofluoric acid may not be immediately evident. HF interferes with nerve function and burns may not initially be painful. Accidental exposures can go unnoticed, delaying treatment and increasing the extent and seriousness of the injury.<ref name="pmid11505130">{{cite journal |author=Yamashita M, Yamashita M, Suzuki M, Hirai H, Kajigaya H |title=Iontophoretic delivery of calcium for experimental hydrofluoric acid burns |journal=Crit. Care Med. |volume=29 |issue=8 |pages=1575–8 |year=2001 |pmid=11505130|doi=10.1097/00003246-200108000-00013}}</ref> Death can occur if as little as 2.5% of [[total body surface area]] is exposed to concentrated HF, while [[hypocalcemia]] and [[hypomagnesemia]] can occur from smaller surface area or lower concentrations.[http://www.emedicine.com/emerg/topic804.htm] Hydrogen fluoride is released upon combustion of fluorine-containing compounds such as products containing [[Viton]] and [[Polytetrafluoroethylene|Teflon]] parts. [[Hydrogen fluoride]] converts immediately to hydrofluoric acid upon contact with water.
HF [[chemical burn]]s can be treated with a water wash and 2.5% [[calcium gluconate]] gel<ref name="pmid2741315">{{cite journal |author=el Saadi MS, Hall AH, Hall PK, Riggs BS, Augenstein WL, Rumack BH |title=Hydrofluoric acid dermal exposure |journal=Vet Hum Toxicol |volume=31 |issue=3 |pages=243–7 |year=1989 |pmid=2741315 |doi=}}</ref><ref name="pmid17091088">{{cite journal |author=Roblin I, Urban M, Flicoteau D, Martin C, Pradeau D |title=Topical treatment of experimental hydrofluoric acid skin burns by 2.5% calcium gluconate |journal=J Burn Care Res |volume=27 |issue=6 |pages=889–94 |year=2006 |pmid=17091088 |doi=10.1097/01.BCR.0000245767.54278.09 |doi_brokendate=2008-06-20}}</ref><ref> {{cite web|url=http://www.research.northwestern.edu/ors/emerg/firstaid/calglugel.htm |title=Calcium Gluconate Gel as an Antidote to HF Acid Burns |accessdate=2008-01-03 |publisher=Northwestern University }}</ref> or special rinsing solutions.<ref name="pmid15461243">{{cite journal |author=Hultén P, Höjer J, Ludwigs U, Janson A |title=Hexafluorine vs. standard decontamination to reduce systemic toxicity after dermal exposure to hydrofluoric acid |journal=J. Toxicol. Clin. Toxicol. |volume=42 |issue=4 |pages=355–61 |year=2004 |pmid=15461243 |doi=}}</ref><ref> {{cite journal|title=News & Views|journal=Chemical Health and Safety |date=September-October 2005|first=|last=|coauthors=|volume= 12|issue=5|pages=35–37| doi = 10.1016/j.chs.2005.07.007 |accessdate=2008-01-03 }}</ref>
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==References==
{{Reflist}}
==External links==
* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc02/icsc0283.htm International Chemical Safety Card 0283]
* [http://www.npi.gov.au/database/substance-info/profiles/44.html National Pollutant Inventory - Fluoride and compounds fact sheet]
* [http://www.cdc.gov/niosh/npg/npgd0334.html NIOSH Pocket Guide to Chemical Hazards]
* {{PubChemLink|14917}} (HF)
* {{PubChemLink|144681}} (5HF)
* {{PubChemLink|141165}} (6HF)
* {{PubChemLink|144682}} (7HF)
* [http://www.compchemwiki.org/index.php?title=Hydrogen_fluoride Computational Chemistry Wiki]
* [http://content.nejm.org/cgi/reprint/356/6/e5.pdf Hydrofluoric Acid Burn, The New England Journal of Medicine] Acid burn case study
* MSDS [[http://msds.dupont.com/msds/pdfs/EN/PEN_09004a2f801b4efc.pdf]]
[[Category:Hydrogen compounds]]
[[Category:Fluorides]]
[[Category:Acids]]
[[Category:Nonmetal halides]]
[[ja:フッ化水素酸]]
[[cs:Kyselina fluorovodíková]]
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[[es:Ácido fluorhídrico]]
[[fr:Acide fluorhydrique]]
[[it:acido fluoridrico]]
[[he:חומצה הידרופלואורית]]
[[nl:Waterstoffluoride]]
[[nn:Flussyre]]
[[pl:Kwas fluorowodorowy]]
[[ru:Плавиковая кислота]]
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[[sl:Fluorovodikova kislina]]
[[fi:Fluorivetyhappo]]
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