Ammonium fluoride

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Ammonium fluoride
The ammonium cation The fluoride anion
ball-and-stick model of an ammonium cation (left) and a fluoride anion (right)
Solid sample of ammonium fluoride
Identifiers
CAS number 12125-01-8 YesY
ChemSpider 23806 YesY
EC number 235-185-9
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
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
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
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 noted otherwise, 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[edit]

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[edit]

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 recombine to give ammonium fluoride, i.e. the reaction is reversible:

[NH4]F ↔ NH3 + HF

Uses[edit]

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[edit]

  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.