Ammonium fluoride

Ammonium fluoride

Names
IUPAC name Ammonium fluoride
Other names Neutral ammonium fluoride
Identifiers
CAS Number	12125-01-8
3D model (Jmol)	Interactive image
ChemSpider	23806
ECHA InfoCard	100.031.975
EC Number	235-185-9
RTECS number	BQ6300000
UN number	2505
InChI InChI=1S/FH.H3N/h1H;1H3 Key: LDDQLRUQCUTJBB-UHFFFAOYSA-N InChI=1/FH.H3N/h1H;1H3 Key: LDDQLRUQCUTJBB-UHFFFAOYAM
SMILES [F-].[NH4+]
Properties
Chemical formula	NH4F
Molar mass	37.037 g/mol
Appearance	White crystalline solid hygroscopic
Density	1.009 g/cm^3
Melting point	100 °C (212 °F; 373 K) (decomposes)
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
Safety data sheet	ICSC 1223
EU classification (DSD)	Toxic (T)
R-phrases	R23/24/25
S-phrases	(S1/2), S26, S45
NFPA 704	0 3 0
Flash point	Non-flammable
Related compounds
Other anions	Ammonium chloride Ammonium bromide Ammonium iodide
Other cations	Sodium fluoride Potassium fluoride
Related compounds	Ammonium bifluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.

Crystal structure

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.^[1] This structure is very similar to ice, and ammonium fluoride is the only substance which can form mixed crystals with water.^[2]

Reactions

On passing hydrogen fluoride gas (in excess) through the salt, ammonium fluoride absorbs the gas to form the addition compound ammonium bifluoride. 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 can recombine to give ammonium fluoride, i.e. the reaction is reversible:

[NH₄]F ⇌ NH₃ + HF

Uses

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.

It is also used for preserving wood, as a mothproofing agent, in printing and dying textiles, and as an antiseptic in breweries.^[3]

References

1. A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
2. Brill, R.; Zaromb, S. "Mixed Crystals of Ice and Ammonium Fluoride". Nature. 173 (4398): 316–317. doi:10.1038/173316a0.
3. 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.