Ammonium fluoride is the inorganic compound

Inorganic compound

Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 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.. This structure is very similar to ice

Ice

Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

, and ammonium fluoride is the only substance which can form mixed crystals with the water.

Reactions

On passing hydrogen fluoride

Hydrogen fluoride

Hydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...

 gas (in excess) through the salt, ammonium fluoride absorbs the gas to form the addition compound  ammonium hydrogen fluoride

Ammonium hydrogen fluoride

Ammonium hydrogen fluoride is the inorganic compound with the formula NH4HF2 or NH4F·HF. It is produced from ammonia and hydrogen fluoride. This colourless salt is a glass-etchant and an intermediate in a once-contemplated route to hydrofluoric acid....

. 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 silicate

Silicate

A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

s. 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 textile

Textile

A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

s, and as an antiseptic

Antiseptic

Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...

 in breweries

Brewery

A brewery is a dedicated building for the making of beer, though beer can be made at home, and has been for much of beer's history. A company which makes beer is called either a brewery or a brewing company....

.