- Ammonium fluoride
Ammonium fluoride Identifiers CAS number ChemSpider EC number UN number 2505 RTECS number BQ6300000 Jmol-3D images Image 1 Properties Molecular formula NH4F Molar mass 37.037 g/mol Appearance White crystalline solid
Density 1.009 g/cm3 Melting point
100 °C (decomp)
Solubility in water 45.3 g/100 ml (25 °C) Solubility slightly soluble in alcohol, insoluble in liquid ammonia Structure Crystal structure Wurtzite structure (hexagonal) Hazards MSDS ICSC 1223 EU Index 009-006-00-8 EU classification Toxic (T) R-phrases S-phrases , , NFPA 704 Flash point Non-flammable Related compounds Other anions Ammonium chloride
Other cations Sodium fluoride
Related compounds Ammonium bifluoride (what is: /?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 the water.
On passing hydrogen fluoride gas (in excess) through the salt, ammonium fluoride absorbs the gas to form the addition compound ammonium hydrogen fluoride. The reaction occurring is:
- 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 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.
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