View source for Chemistry:Ammonium bifluoride

{{Chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 401799201
| ImageFileL1    = Ammonium-3D-vdW.png
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageNameL1    = Space fill model of the ammonium cation
| ImageFileR1    = Hydrogendifluoride-3D-vdW.png
| ImageFileR1_Ref = {{chemboximage|correct|??}}
| ImageNameR1    = Space fill model of the bifluoride anion
| ImageFile2     = Sample of Ammonium bifluoride.jpg
| ImageName2     = Sample of Ammonium bifluoride
| ImageFile3     = Ammonium-bifluoride-xtal-unit-cell-3D-bs-17.png
| IUPACName      = Ammonium bifluoride
| OtherNames     = {{ubl|Ammonium acid fluoride|Ammonium hydrofluoride|Ammonium difluoride|Ammonium hydrogendifluoride|Ammonium hydrogen difluoride}}
| Section1       = {{Chembox Identifiers
| CASNo = 1341-49-7
| CASNo_Ref = {{cascite|correct|CAS}}
| ChemSpiderID = 21241205
| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
| EC_number = 215-676-4
| UNNumber = 1727
| UNII = C2M215358O
| PubChem = 14935
| SMILES = [NH4+].F[H-]F
| SMILES1 = [F-].F.[NH4+]
| StdInChI = 1S/F2H.H3N/c1-3-2;/h;1H3/q-1;/p+1
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| InChI = 1/2FH.H3N/h2*1H;1H3
| StdInChIKey = XIONBZYFLSJNBW-UHFFFAOYSA-O
| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
| InChIKey = KVBCYCWRDBDGBG-UHFFFAOYAG}}
| Section2       = {{Chembox Properties
| Formula = {{chem2|[NH4][HF2]}}
| H=5 | F=2 | N=1
| Appearance = Colourless crystals
| Density = 1.50 g cm<sup>−3</sup>
| Solubility = 63g/(100 ml) (20&nbsp;°C)
| SolubleOther = slightly soluble
| Solvent = alcohol
| MeltingPtC = 126
| BoilingPtC = 240
| BoilingPt_ref = (decomposes)
| RefractIndex = 1.390
 }}
| Section3       = {{Chembox Structure
| Coordination = [[Chemistry:Ammonium|{{chem2|[NH4]+}}]] cation: tetrahedral<br />[[Chemistry:Bifluoride|{{chem2|[HF2]−}}]] anion: linear
| CrystalStruct = Cubic, related to the [[Chemistry:Caesium chloride|CsCl]] structure
 }}
| Section7       = {{Chembox Hazards
| GHSPictograms = {{GHS05}}{{GHS06}}<ref name="sigma">{{Sigma-Aldrich|id=455830 |name=Ammonium bifluoride |accessdate=2013-07-20}}</ref>
| HPhrases = {{H-phrases|301|314}}<ref name="sigma" />
| PPhrases = {{P-phrases|280|301+310|305+351+338|310}}<ref name="sigma" />
| ExternalSDS = 
| MainHazards = 
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S = 
| FlashPt = 
| AutoignitionPt = 
| ExploLimits = 
| LD50 =
| PEL = 
 }}
| Section8       = {{Chembox Related
| OtherCations = [[Chemistry:Potassium bifluoride|potassium bifluoride]]
| OtherCompounds = [[Chemistry:Ammonium fluoride|ammonium fluoride]]
 }}
}}
'''Ammonium bifluoride''' is the [[Chemistry:Inorganic compound|inorganic compound]] with the formula {{chem2|[NH4][HF2]}} or {{chem2|[NH4]F*HF}}. It is produced from [[Chemistry:Ammonia|ammonia]] and [[Chemistry:Hydrogen fluoride|hydrogen fluoride]]. This colourless salt is a glass-etchant and an intermediate in a once-contemplated route to [[Chemistry:Hydrofluoric acid|hydrofluoric acid]].

== Structure ==
Ammonium bifluoride, as its name indicates, contains an [[Chemistry:Ammonium|ammonium]] cation ({{chem2|[NH4]+}}), and a [[Chemistry:Bifluoride|bifluoride]] or hydrogen(difluoride) anion ({{chem2|[HF2]−}}). The centrosymmetric triatomic bifluoride anion features the strongest known [[Chemistry:Hydrogen bond|hydrogen bond]], with a [[Chemistry:Fluoride|F]]−[[Chemistry:Hydrogen|H]] length of 114 pm.<ref>{{Greenwood&Earnshaw}}</ref> and a bond energy greater than 155 kJ/mol.<ref>Emsley, J. (1980) ''Very Strong Hydrogen Bonds'', Chemical Society Reviews, 9, 91–124. {{doi|10.1039/CS9800900091}}</ref>

In solid {{chem2|[NH4][HF2]}}, each [[Chemistry:Ammonium|ammonium]] cation is surrounded by four fluoride centers in a tetrahedron, with hydrogen-fluorine hydrogen bonds present between the hydrogen atoms of the ammonium ion and the fluorine atoms.<ref>{{ cite journal | title = The electron-density distribution in ammonium bifluoride | first = T. R. R. | last = McDonald | journal = [[Chemistry:Acta Crystallographica|Acta Crystallogr.]] | year = 1960 | volume = 13 | issue = 2 | pages = 113–124 | doi = 10.1107/S0365110X60000261 | doi-access = free | bibcode = 1960AcCry..13..113M }}</ref><ref>{{ Cite journal | url = https://www.ccdc.cam.ac.uk/structures/Search?Ccdcid=1595541&DatabaseToSearch=Published | title = ICSD Entry: 14140 | website = [[Biology:Cambridge Structural Database|Cambridge Structural Database]]: Access Structures | publisher = [[Organization:Cambridge Crystallographic Data Centre|Cambridge Crystallographic Data Centre]] | access-date = 2022-06-25 }}</ref> Solutions contain tetrahedral [[Chemistry:Ammonium|{{chem2|[NH4]]]+}} cations and linear [[Chemistry:Bifluoride|{{chem2|[HF2]−}}]] anions.

== Production and applications ==
Ammonium bifluoride is a component of some etchants. It attacks [[Chemistry:Silica|silica]] component of glass:
:{{chem2|[[Chemistry:Silicon dioxide|SiO2]] + 4 [NH4][HF2] → [[Chemistry:Silicon tetrafluoride|SiF4]] + 4 [[Chemistry:Ammonium fluoride|[NH4]F]] + 2 [[Chemistry:Water|H2O]]}}
[[Chemistry:Potassium bifluoride|Potassium bifluoride]] is a related more commonly used etchant.

Ammonium bifluoride has been considered as an intermediate in the production of [[Chemistry:Hydrofluoric acid|hydrofluoric acid]] from [[Chemistry:Hexafluorosilicic acid|hexafluorosilicic acid]]. Thus, hexafluorosilicic acid is hydrolyzed to give ammonium fluoride, which thermally decomposes to give the bifluoride:
:{{chem2|H2[SiF6] + 6 [[Chemistry:Ammonia|NH3]] + 2 H2O → SiO2 + 6 [NH4]F}}
:{{chem2|2 [NH4]F → NH3 + [NH4][HF2]}}
The resulting ammonium bifluoride is converted to [[Chemistry:Sodium bifluoride|sodium bifluoride]], which thermally decomposes to release HF.<ref name=Aigueperse>{{Ullmann|doi=10.1002/14356007.a11_307|title=Fluorine Compounds, Inorganic|year=2000|last1=Aigueperse|first1=Jean|last2=Mollard|first2=Paul|last3=Devilliers|first3=Didier|last4=Chemla|first4=Marius|last5=Faron|first5=Robert|last6=Romano|first6=René|last7=Cuer|first7=Jean Pierre|isbn=3527306730}}</ref>

Ammonium bifluoride is also used as an additive in tin-nickel plating processes as the fluoride ion acts as a complexing agent with the tin, allowing for greater control over the resulting composition and finish.

== Toxicity ==
Ammonium bifluoride is toxic to consume and a skin corrosion agent. Upon exposure to skin, rinsing with water followed by a treatment of [[Chemistry:Calcium gluconate|calcium gluconate]] is required.<ref name="sigma" /> In water, ammonium bifluoride exists in [[Chemistry:Chemical equilibrium|chemical equilibrium]] with [[Chemistry:Hydrofluoric acid|hydrofluoric acid]] and heating releases [[Chemistry:Hydrogen fluoride|hydrogen fluoride]] gas.<ref name=":1">{{cite web |title=Bifluorides: Human health tier II assessment |author=National Industrial Chemicals Notification and Assessment Scheme |url=https://www.industrialchemicals.gov.au/sites/default/files/Bifluorides_Human%20health%20tier%20II%20assessment.pdf#page=2 |date=April 17, 2020 |access-date=February 8, 2023 |publisher=Department of Health (Australia)}}</ref> Consequently, there is an equivalent toxicological risk as is present with hydrofluoric acid, and the same safety precautions apply.<ref name=":0">{{cite journal |last1=Genuino |first1=Homer C. |last2=Opembe |first2=Naftali N. |last3=Njagi |first3=Eric C. |last4=McClain |first4=Skye |last5=Suib |first5=Steven L. |year=2012 |title=A review of hydrofluoric acid and its use in the car wash industry |url=https://www.sciencedirect.com/science/article/pii/S1226086X12001189 |journal=Journal of Industrial and Engineering Chemistry |language=en |volume=18 |issue=5 |pages=1529–1539 |doi=10.1016/j.jiec.2012.03.001 |issn=1226-086X}}</ref><ref name=":1" />

Ammonium bifluoride is used in some automotive wheel cleaning products. Many injuries have resulted in users not being aware of the risks posed by the products.<ref>{{cite magazine |last=Gormley |first=James |date=May 29, 2001 |title=The truth about ammonium bifluoride |url=http://www.carwash.com/article.asp?IndexID=6631269 |url-status=dead |magazine = Professional Car Washing and Detailing |archive-date=2001-05-29 |access-date=  |archive-url=https://web.archive.org/web/20010529123319/http://www.carwash.com/article.asp?IndexID=6631269}}</ref> Ammonium bifluoride based products are often considered a safer alternative to hydrofluoric acid, yet still pose clear risks to the handler.<ref name=":0" />  Ammonium bifluoride, ammonium fluoride, and hydrofluoric acid have been described as "too dangerous for any use in a car wash environment" by ''Professional Car Washing and Detailing'' magazine,<ref>{{cite magazine|title = The Five Factors of Clean: Chemistry, Part 1|first = Ryan|last = Cook|date = October 9, 2013|access-date = February 8, 2023|magazine = Professional Car Washing and Detailing|url = https://www.carwash.com/the-five-factors-of-clean-chemistry-part-1/}}</ref> advice that accords with a 2015 report from the U.S. Centers for Disease Control and Prevention.<ref>{{cite magazine|title = OSHA gives employees the right to know|first = Maria|last = Woodie|date = December 1, 2015|access-date = February 8, 2023|magazine = Professional Car Washing and Detailing|url = https://www.carwash.com/osha-gives-emp-right-to-know/}}</ref>

== References ==
{{reflist}}

{{fluorine compounds}}

[[Category:Nonmetal halides]]
[[Category:Ammonium compounds]]

{{Sourceattribution|Ammonium bifluoride}}