Ammonium bicarbonate

From Wikipedia, the free encyclopedia
Jump to: navigation, search

Ammonium bicarbonate is an inorganic compound with formula (NH4)HCO3. The compound has many names, reflecting its long history. Chemically speaking, it is the bicarbonate salt of ammonium. It is a colourless solid that degrades readily to carbon dioxide and ammonia.

Ammonium bicarbonate
2D model of ammonium bicarbonate
Ball-and-stick model of the ammonium cation Ball-and-stick model of the bicarbonate anion
Identifiers
CAS number 1066-33-7 YesY
ChemSpider 13395 YesY
UNII 45JP4345C9 YesY
RTECS number BO8600000
Jmol-3D images Image 1
Properties
Molecular formula NH4HCO3
Molar mass 79.056 g/mol
Density 1.586 g/cm3
Melting point 41.9 °C, 315 K, decomp.
Solubility in water 11.9 g/100 mL (0 °C)
21.6 g/100 mL (20 °C)
36.6 g/100 mL (40 °C)
Solubility insoluble in methanol
Hazards
MSDS ICSC 1333
GHS pictograms GHS-pictogram-exclam.svg[1]
GHS hazard statements H302[1]
GHS precautionary statements none[1]
EU Index Not listed
Main hazards Decomposes to release ammonia
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform 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 carbonate
Other cations Sodium bicarbonate
Potassium bicarbonate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Production[edit]

Ammonium bicarbonate is produced by combining carbon dioxide and ammonia:

CO2 + NH3 + H2O → (NH4)HCO3

Since ammonium bicarbonate is thermally unstable, the reaction solution is kept cold, which allows the precipitation of the product as white solid. About 100,000 tons were produced in this way in 1997.[2]

Ammonia gas passed into a strong aqueous solution of the sesquicarbonate (a 2:1:1 mixture of (NH4)HCO3, (NH4)2CO3, and H2O) and converts it into normal ammonium carbonate ((NH4)2CO3), which can be obtained in the crystalline condition from a solution prepared at about 30 °C. This compound on exposure to air gives off ammonia and reverts to ammonium bicarbonate.

Salt of Hartshorn[edit]

Compositions containing ammonium carbonate have long been known. They were once produced commercially, formerly known as sal volatile or salt of hartshorn. It was obtained by the dry distillation of nitrogenous organic matter such as hair, horn, leather. In addition to ammonium bicarbonate, this material contains ammonium carbamate (NH4CO2NH2), and ammonium carbonate ((NH4)2CO3). It is sometimes called ammonium sesquicarbonate. It possesses a strong ammoniacal smell, and on digestion with alcohol, the carbamate is dissolved leaving a residue of ammonium bicarbonate.[2]

A similar decomposition taking place when the sesquicarbonate is exposed to air.

Uses[edit]

Ammonium bicarbonate is used in the food industry as a raising agent for flat baked goods, such as cookies and crackers, and in China in steamed buns and Chinese almond cookies. It was commonly used in the home before modern day baking powder was made available. In China it is called edible or food-grade "smelly powder". Many baking cookbooks (especially from Scandinavian countries) may still refer to it as hartshorn or hornsalt [3][4] (e.g., FI: "hirvensarvisuola", NO: "hjortetakksalt", SE: "hjorthornssalt", "salt of hart's horn") In many cases it may be substituted with baking soda or baking powder or a combination of both, depending on the recipe composition and leavening requirements.[5] Compared to baking soda or potash, hartshorn has the advantage of producing more gas for the same amount of agent, and of not leaving any salty or soapy taste in the finished product, as it completely decomposes into water and gaseous products that evaporate during baking. It cannot be used for moist, bulky baked goods however, such as normal bread or cakes, since some ammonia will be trapped inside and will cause an unpleasant taste.

It is commonly used as an inexpensive nitrogen fertilizer in China, but is now being phased out in favor of urea for quality and stability. This compound is used as a component in the production of fire-extinguishing compounds, pharmaceuticals, dyes, pigments, and it is also a basic fertilizer being a source of ammonia. Ammonium bicarbonate is still widely used in the plastic and rubber industry, in the manufacture of ceramics, in chrome leather tanning, and for the synthesis of catalysts.[citation needed]

It is also used for buffering solutions to slightly alkaline pH during chemical purification, such as High Performance Liquid Chromatography. Because it entirely decomposes to volatile compounds this allows rapid recovery of the compound of interest by freeze-drying.

Ammonium bicarbonate is also a key component of the expectorant cough syrup "Senega and Ammonia".

Reactions[edit]

It dissolves in water to give a mildly alkaline solution. It is insoluble in acetone and alcohols.

Ammonium bicarbonate decomposes above about 36 °C into ammonia, carbon dioxide, and water in an endothermic process and so causes a drop in the temperature of the water:

NH4HCO3 → NH3 + H2O + CO2.

When treated with acids, carbon dioxide is also produced:

NH4HCO3 + HCl → NH4Cl + CO2 + H2O.

Reaction with base produces ammonia.

It reacts with sulfates of alkaline-earth metals to precipitating their carbonates:

CaSO4 + 2 NH4HCO3CaCO3 + (NH4)2SO4 + CO2 + H2O.

It also reacts with alkali metal halides, giving alkali metal bicarbonate and ammonium halide:

NH4HCO3 + NaClNH4Cl + NaHCO3;
NH4HCO3 + KINH4I + KHCO3;
NH4HCO3 + NaBrNH4Br + NaHCO3.

Safety[edit]

Ammonium Bicarbonate is an irritant to the skin, eyes and respiratory system. Short-term health effects may occur immediately or shortly after exposure to Ammonium Bicarbonate. Breathing Ammonium Bicarbonate can irritate the nose, throat and lungs causing coughing, wheezing and/or shortness of breath. Repeated exposure may cause bronchitis to develop with cough, and/or shortness of breath. Health effects can occur some time after exposure to Ammonium Bicarbonate and can last for months or years.

No exposure limits have been established for Ammonium Bicarbonate. This however, does not mean that this substance is not harmful. Safe work practices are recommended and should be followed at all times.

Where possible, operations should be enclosed and the use of local exhaust ventilation at the site of chemical release is recommended. If local exhaust ventilation or enclosure is not used, respirators are necessary. Wear protective work clothing. Change clothes and wash thoroughly immediately after exposure to Ammonium Bicarbonate.[6]

Ammonium Bicarbonate from China used to make "cookies" was found to be contaminated with melamine, and imports were banned in Malaysia following the 2008 Chinese milk scandal.

References[edit]

  1. ^ a b c Sigma-Aldrich Co., Ammonium bicarbonate. Retrieved on 2013-07-20.
  2. ^ a b Zapp, Karl-Heinz; Wostbrock, Karl-Heinz; Schäfer, Manfred; Sato, Kimihiko; Seiter, Herbert; Zwick, Werner; Creutziger, Ruthild; Leiter, Herbert (2000). "Ammonium Compounds". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a02_243. ISBN 3527306730 
  3. ^ "Naturfag : Hornsalt øvelse" [Science: Hornsalt exercise] (in Norwegian). Studenttorget.no. November 26, 2003. Retrieved March 3, 2013. 
  4. ^ "Science: Hornsalt exercise" translated into English
  5. ^ "What is hartshorn?". Archived from the original on 1 April 2007. Retrieved 2007-03-19. 
  6. ^ Bicarbonate, Ammonium. "Hazardous Substance Fact Sheet". New Jersey Department of Health and Senior Services.