Hexafluorosilicic acid
4435988
219871064
2008-06-17T06:37:38Z
JohnI
790954
britian => britain
{{Chembox new
| Name = Dihydrogen hexafluorosilicate
| ImageFile =
<!-- | ImageSize = 200px -->
| ImageName =
| IUPACName = Dihydrogen hexafluorosilicate
| OtherNames = Hexafluorosilicic acid<br />fluorosilicic acid<br/>fluosilicic acid
| Section1 = {{Chembox Identifiers
| CASNo = 16961-83-4
| RTECS = VV8225000
}}
| Section2 = {{Chembox Properties
| Formula = H<sub>2</sub>F<sub>6</sub>Si
| MolarMass = 144.0922 g/mol
| Appearance = colourless solution
| Density = 1.22 g/cm<sup>3</sup> 25% aqueous soln
| pKa =
}}
| Section3 = {{Chembox Structure
| MolShape = Octahedral SiF<sub>6</sub><sup>2<nowiki>−</nowiki></sup>
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://ptcl.chem.ox.ac.uk/MSDS/DI/dihydrogen_hexafluorosilicate.html External MSDS]
| MainHazards = Toxic, corrosive.
| FlashPt = Non-flammable.
| RPhrases = {{R20}}, {{R21}}, {{R22}}, {{R34}}, {{R41}}
| SPhrases = {{S26}}, {{S27}}
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Hydrofluoric acid|HF]]<br />[[Hexafluorophosphoric acid|HPF<sub>6</sub>]]<br />[[Fluoroboric acid|HBF<sub>4</sub>]]
}}
}}
'''Hexafluorosilicic acid''' is the [[chemical compound]] with the formula H<sub>2</sub>SiF<sub>6</sub>. The free acid is encountered as an equilibrium mixture with hexaflurorosilicate anion (SiF<sub>6</sub><sup>2<nowiki>−</nowiki></sup>) only in solution in solvents that are proton donors<ref>{{cite journal | doi = 10.1149/1.2083227 | author = J. P. Nicholson | title = Electrodeposition of Silicon from Nonaqueous Solvents | journal = [[J. Electrochem. Soc.]] | volume = 152 | issue = 12 | pages = C795-C802 | year = 2005}}</ref> at low pH. In aqueous solution, evaporation of H<sub>2</sub>SiF<sub>6</sub> results in loss of HF and [[Silicon tetrafluoride|SiF<sub>4</sub>]].
H<sub>2</sub>SiF<sub>6</sub> is a by-product from the reaction of [[fluoroapatite]] with [[sulfuric acid]], which produces [[HF]], which in turn reacts with silicate minerals:
:SiO<sub>2</sub> + 6 HF → H<sub>2</sub>SiF<sub>6</sub> + 2 H<sub>2</sub>O
Aqueous solutions of H<sub>2</sub>SiF<sub>6</sub> contain the hexafluorosilicate anion, SiF<sub>6</sub><sup>2<nowiki>−</nowiki></sup>. In this octahedral anion, the Si-F bond distances are 1.71 [[Å]].<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref>
==Uses==
H<sub>2</sub>SiF<sub>6</sub> is commonly used for [[water fluoridation]] in several countries including the United States, Great Britain, and Ireland.<!-- is this peculiar to the United States? If not, needs to be generalized--><!-- I did not locate a comprehensive list -->
H<sub>2</sub>SiF<sub>6</sub> is a [[reagent]] in [[organic synthesis]] for cleaving Si-O bonds of silyl ethers. It is more reactive for this purpose than [[HF]]. It reacts faster with t-butyldimethysilyl (TBDMS) ethers than triisopropylsilyl (TIPS) ethers.<ref>Pilcher, A. S.; DeShong, P. “Fluorosilicic Acid” in Encyclopedia of Reagents for Organic Synthesis, Copyright © 2001 John Wiley & Sons. DOI: 10.1002/047084289X.rf013</ref>
Hexafluorosilicic acid and the salts are used as wood preservation agents. The aluminium and magnesium hexafluorosilicate are two used compounds. <ref>{{cite journal
| title = Modification of wood with silicon compounds. inorganic silicon compounds and sol-gel systems: a review
| author = Carsten Mai, Holger Militz
| journal = Wood Science and Technology
| volume = 37
| issue = 5
| pages =
| year = 2004
| url =
| doi = 10.1007/s00226-003-0205-5 }}</ref>
==Safety==
Hexafluorosilicic acid releases [[hydrogen fluoride]] when evaporated, so it has similar risks. It is corrosive and may cause [[fluoride poisoning]]; inhalation of the vapors may cause lung edema. Like hydrogen fluoride, it attacks glass and stoneware.<ref>Hexafluorosilicic acid Chemical Safety Card http://www.cdc.gov/niosh/ipcsneng/neng1233.html</ref>
==References==
<references/>
[[Category:Hydrogen compounds]]
[[Category:Fluorides]]
[[Category:Silicates]]
[[Category:Acids]]
[[Category:Coordination compounds]]
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[[de:Hexafluorokieselsäure]]
[[it:Acido fluorosilicico]]
[[zh:氟硅酸]]