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Hydrofluoric acid
Hydrofluoric acid

Determination of silicon dioxide. Metallurgical metallographic analysis. Silicon compounds. Manufacture of fluoride.

Hydrofluoric acidIdentifiersPropertiesHazardsRelated compounds
 
Other names[hide]

fluoric acid; fluorhydric acid

CAS number7664-39-3 Y
ChemSpider14214 Y
UNIIRGL5YE86CZ Y
EC number231-634-8
ChEBICHEBI:29228 Y
RTECS numberMW7875000
Jmol-3D imagesImage 1
SMILES[show]

F

 

 

 

InChI[show]

InChI=1S/FH/h1H YKey: KRHYYFGTRYWZRS-UHFFFAOYSA-N Y

InChI=1/FH/h1HKey: KRHYYFGTRYWZRS-UHFFFAOYAC

Molecular formulaHF (aq)
Molar massnot applicable(see hydrogen fluoride)
AppearanceColorless solution
Density1.15 g/mL (for 48% soln.)
Melting point

not applicable(see hydrogen fluoride)

Boiling point

not applicable(see hydrogen fluoride)

Solubility in waterMiscible.
Acidity (pKa)3.17 [1]
MSDSduPont MSDS
EU Index009-003-00-1
EU classificationVery toxic (T+)Corrosive (C)
R-phrasesR26/27/28, R35
S-phrases(S1/2), S7/9, S26, S36/37, S45
NFPA 704042COR
Flash pointNon-flammable
Other anionsHydrochloric acidHydrobromic acidHydroiodic acid
Related compoundsHydrogen fluoride
 Y (verify) (what is: Y/N?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Hydrofluoric acid is a highly corrosive acid, capable of dissolving many materials, especially oxides. Its ability to dissolve glass has been known since the 17th century, even before hydrofluoric acid had been prepared in large quantities by Carl Wilhelm Scheele in 1771.[2] Because of its high reactivity toward glass and moderate reactivity toward many metals, hydrofluoric acid is usually stored in plastic containers (although PTFE is slightly permeable to it).[3]

Acidity

Hydrofluoric acid is classified as a weak acid because of its lower dissociation constant compared to the strong acids. It ionizes in aqueous solution in a similar fashion to other common acids:[4]

HF + H2O H3O+ + F−

It is the only hydrohalic acid that is not considered a strong acid, i.e. it does not fully ionize in dilute aqueous solutions.

When the concentration of HF approaches 100%, the acidity increases dramatically because of the following equilibrium:

2 HF H+ + FHF−

The bifluoride (FHF−) anion is stabilized by the very strong hydrogen–fluorine hydrogen bond.

[edit] Production

Hydrofluoric acid is produced by treatment of the mineral fluorite (CaF2) with concentrated sulfuric acid. When combined at 265 °C, these two substances react to produce hydrogen fluoride and calcium sulfate according to the following chemical equation:

CaF2 + H2SO4 → 2 HF + CaSO4

Although bulk fluorite is a suitable precursor and a major source of world HF production, HF is also produced as a by-product of the production of phosphoric acid, which is derived from the mineral apatite. Apatite sources typically contain a few percent of fluoroapatite, acid digestion of which releases gaseous stream consisting of sulfur dioxide (from the H2SO4), water, and HF, as well as particulates. After separation from the solids, the gases are treated with sulfuric acid and oleum to afford anhydrous HF. Owing to the corrosive nature of HF, its production is accompanied by the dissolution of silicate minerals, and, in this way, significant amounts of fluorosilicic acid is generated.[3]

Hydrofluoric acid

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