Ammonium hydrogen fluoride is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemis ...

with the formula or . It is produced from

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...

and

hydrogen fluoride Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock ...

. This colourless salt is a glass- etchant and an intermediate in a once-contemplated route to

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepres ...

Structure

Ammonium bifluoride, as its name indicates, contains an

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaterna ...

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

(), and a bifluoride or hydrogen(difluoride)

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

(). The centrosymmetric triatomic bifluoride anion features the strongest known

hydrogen bond In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...

, with a F− H length of 114 pm. and a bond energy greater than 155 kJ/mol. In solid , each

cation is surrounded by four fluoride centers in a tetrahedron, with hydrogen-fluorine

hydrogen bonds In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...

present between the hydrogen atoms of the ammonium ion and the fluorine atoms. Solutions contain tetrahedral cations and linear anions.

Production and applications

Ammonium bifluoride is a component of some etchants. It attacks silica component of glass: : Potassium bifluoride is a related more commonly used etchant. Ammonium bifluoride has been considered as an intermediate in the production of

from hexafluorosilicic acid. Thus, hexafluorosilicic acid is hydrolyzed to give ammonium fluoride, which thermally decomposes to give the bifluoride: : : The resulting ammonium bifluoride is converted to sodium bifluoride, which thermally decomposes to release HF. 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 calcium gluconate is required. When dissolved in water it dissociates

meaning there is no difference from a toxicological perspective and the same safety precautions apply as one is handling

. 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. Ammonium bifluoride based products are often considered a safer alternative to hydrofluoric acid, yet still pose clear risks to the handler.

References

{{Ammonium salts Nonmetal halides Ammonium compounds Deliquescent substances Bifluorides