Neutral ammonium fluoride
|Molar mass||37.037 g/mol|
|Appearance||White crystalline solid
|Melting point||100 °C (212 °F; 373 K) (decomposes)|
|45.3 g/100 ml (25 °C)|
|Solubility||slightly soluble in alcohol, insoluble in liquid ammonia|
|Crystal structure||Wurtzite structure (hexagonal)|
|EU classification||Toxic (T)|
|S-phrases||(S1/2), S26, S45|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Ammonium fluoride is the inorganic compound with the formula NH4F. It crystallizes as small colourless prisms, having a sharp saline taste, and is exceedingly soluble in water.
Ammonium fluoride adopts the wurtzite crystal structure, in which both the ammonium cations and the fluoride anions are stacked in ABABAB... layers, each being tetrahedrally surrounded by four of the other. There are NH...F hydrogen bonds between the anions and cations. This structure is very similar to ice, and ammonium fluoride is the only substance which can form mixed crystals with water.
- NH4F + HF → NH4HF2
It sublimes when heated—a property common among ammonium salts. In the sublimation, the salt decomposes to ammonia and hydrogen fluoride, and the two gases can recombine to give ammonium fluoride, i.e. the reaction is reversible:
- [NH4]F ⇌ NH3 + HF
This substance is commonly called "commercial ammonium fluoride". The word "neutral" is sometimes added to "ammonium fluoride" to represent the neutral salt—[NH4]F vs. the "acid salt" (NH4HF2). The acid salt is usually used in preference to the neutral salt in the etching of glass and related silicates. This property is shared among all soluble fluorides. For this reason it cannot be handled in glass test tubes or apparatus during laboratory work.
- A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
- Brill, R.; Zaromb, S. "Mixed Crystals of Ice and Ammonium Fluoride". Nature 173 (4398): 316–317. doi:10.1038/173316a0.
- Aigueperse, Jean; Paul Mollard; Didier Devilliers; Marius Chemla; Robert Faron; Renée Romano; Jean Pierre Cuer (2005). "Fluorine Compounds, Inorganic". In Ullmann. Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307.