Ammonium fluoride

Ammonium fluoride
IUPAC name Ammonium fluoride
Other names Neutral ammonium fluoride
Identifiers
CAS number	12125-01-8 Y
ChemSpider	23806 Y
EC number	235-185-9
UN number	2505
RTECS number	BQ6300000
Jmol-3D images	Image 1
SMILES [F-].[NH4+]
InChI InChI=1S/FH.H3N/h1H;1H3 Y Key: LDDQLRUQCUTJBB-UHFFFAOYSA-N Y InChI=1/FH.H3N/h1H;1H3 Key: LDDQLRUQCUTJBB-UHFFFAOYAM
Properties
Molecular formula	NH4F
Molar mass	37.037 g/mol
Appearance	White crystalline solid hygroscopic
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	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
Y fluoride (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

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 the water.^[2]

Reactions

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

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.