Sunday, April 8, 2012

Reactions of Ammonium Fluoride


Ammonium fluorideAmmonium fluoride is a kind of white crystalline solid soluble in water, slightly soluble in alcohol. 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. It is noncombustible but decomposes to ammonia and hydrogen fluoride when heated and to ammonia and ammonium bifluoride in hot water. It reacts with chlorine trifluoride causing explosion hazard and attacks glass and metal. It is corrosive to aluminum. This substance can cause fluoride poisoning. This compound is commonly called 'neutral ammonium fluoride' to represent the neutral salt - [NH4]F. As the acid salt contains a higher percentage of fluoride by mass, it is usually used in preference to the neutral salt in the etching of glass. Ammonium fluoride is used in:
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

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