Ammonium chloride (uh-MOH-ni-um KLOR-ide) occurs as odorless white crystals with a cool, salt-like taste. The compound is of interest to historians of chemistry as being one of the first chemicals mentioned by ancient scholars and the first compound of ammonia to have been discovered. For example, the Roman philosopher Pliny the Elder (23–79 ce) wrote about a substance he called hammoniacus sal that appears to have been ammonium chloride. The problem is that various authorities used the term sal ammoniac for a variety of materials that were clearly different from each other. No one really knew the compound's actual chemical composition until 1700, when it was discovered by the French botanist Joseph Tournefort (1656–1708). In any case, sal ammoniac was an important raw material in early industrial operations, including primarily dyeing and metallurgical operations.
Ammonium muriate; sal ammoniac; salmiac
Nitrogen, hydrogen, chlorine
340°C (640°F; sublimes at melting point)
Soluble in water; slightly soluble in alcohol; insoluble in most organic solvents
Sal ammoniac is also the name of the mineral form of ammonium chloride. The mineral occurs only rarely in nature, and only then in arid (dry) regions. Since ammonium chloride is quite soluble in water, it remains on the ground only in places where there is little rain. One such location is around the vents of active volcanoes. The compound is formed in these regions when hydrogen chloride (HCl) in volcanic gases and ammonia (NH3) produced by the decay of plants and animals react with each other to form ammonium chloride, which then settles out onto the ground.
HOW IT IS MADE
One straightforward method of making ammonium chloride is by combining an aqueous solution of some compound of ammonia, usually ammonium sulfate ([NH4]2SO4), with hydrochloric acid (HCl) and collecting the ammonium chloride that forms by evaporation. Commercially, the compound is obtained as a by-product of the so-called ammonia-soda process for making sodium carbonate (Na2SO4). In this process, invented by the Belgian chemist Ernest Solvay (1838–1922) in 1861, ammonia, sodium chloride (NaCl), and carbon dioxide (CO2) are combined with each other in a series of reactions to make sodium carbonate, a very important commercial product. Ammonium chloride is also formed during the reactions and is removed as a by-product.
COMMON USES AND POTENTIAL HAZARDS
Ammonium chloride has a wide variety of commercial uses. One of the best known uses is in dry cell batteries. Dry cell batteries consist of three parts: the anode (the metal bottom of the battery), the cathode (the metal knob at the top of the battery), and the electrolyte (a moist solid material that makes up the body of the battery). Electrons produced in a chemical reaction within the battery flow out of the cathode, through an external circuit (the device to which the battery is attached), back into the battery through the anode, and back to the cathode through the electrolyte. The electrolyte in a dry cell battery consists of a pasty mixture of ammonium chloride with water.
- Sal ammoniac was an important substance in the study of alchemy. The goals and methods of alchemy changed considerably over the period from about the twelfth century to about the sixteenth century and were somewhat different from culture to culture. For example, one Islamic alchemist, Abu Bakr Mohammed ar-Razi (865–925) classified sal ammoniac as one of the fundamental spirits of matter, along with mercury, sulfur, and arsenic.
Some other uses of ammonium chloride include:
- As a mordant in dyeing and printing operations;
- As a flux for soldering;
- For the production of other ammonium compounds, especially those used as fertilizers;
- In the manufacture of certain types of polymers, especially the family known as the urea-formaldehyde resins;
- For the electroplating of metals; and
- As an additive to a licorice-type candy popular in some parts of the world, to which it gives a characteristic salty taste.
Exposure to ammonium chloride may carry certain health risks. When inhaled or deposited on the skin, it may cause irritation of the tissues that may require treatment. The compound is potentially toxic if swallowed. These potential problems are generally of concern primarily to people who work with the compound directly, as in the industries mentioned above. Anyone who is exposed to ammonium chloride should see medical attention immediately.
Words to Know
- An ancient field of study from which the modern science of chemistry evolved.
- AQUEOUS SOLUTION
- A solution that consists of some material dissolved in water.
- Process by which a thin layer of one metal is deposited on top of a second metal by passing an electric current through a solution of the first metal.
- A material that lowers the melting point of another substance or mixture of substances or that is used in cleaning a metal.
- A substance used in dyeing and printing that reacts chemically with both a dye and the material being dyed to help hold the dye permanently to the material.
- A compound consisting of very large molecules made of one or two small repeated units called monomers.
FOR FURTHER INFORMATION
"Ammonium Chloride: Helping to Provide Portable Electricity." The Science Center. http://www.science-education.org/classroom_activities/chlorine_compound/ammonium_chloride.html (accessed on September 19, 2005).
"Ammonium Chloride, Technical." Zaclon Incorporated. http://www.zaclon.com/pdf/amchltec_datasheet.pdf (accessed on September 19, 2005).
"Material Safety Data Sheet: Ammonium Chloride." Department of Chemistry, Iowa State University. http://avogadro.chem.iastate.edu/MSDS/NH4Cl.htm (accessed on September 19, 2005).
Patnaik, Praydot. Handbook of Inorganic Chemicals. New York: McGraw-Hill, 2003.