- Ammonium bicarbonate
Ammonium bicarbonate Identifiers CAS number ChemSpider UNII 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 hazard statements  GHS precautionary statements none EU Index Not listed Main hazards Decomposes to release ammonia NFPA 704 Flash point Non-flammable Related compounds Other anions Ammonium carbonate Other cations Sodium bicarbonate
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Ammonium bicarbonate, a compound with formula NH4(C(=O)OHO), also called bicarbonate of ammonia, ammonium hydrogen carbonate, hartshorn, AmBic or powdered baking ammonia, is the bicarbonate salt of ammonia.
Ammonium bicarbonate is produced in the process that also leads to ammonium carbonate. Commercial ammonium carbonate was formerly known as sal volatile or salt of hartshorn and was formerly obtained by the dry distillation of nitrogenous organic matter such as hair, horn, decomposed urine, etc., but is now obtained by heating a mixture of sal ammoniac, or ammonium sulfate and chalk, to redness in iron retorts, the vapours being condensed in leaden receivers. The crude product is refined by sublimation, when it is obtained as a white fibrous mass, which consists of a mixture of hydrogen ammonium carbonate, NH4•HCO3, and ammonium carbamate, NH2COONH4, in molecular proportions; on account of its possessing this constitution it is sometimes called ammonium sesquicarbonate. It possesses a strong ammoniacal smell, and on digestion with alcohol the carbamate is dissolved and a residue of ammonium bicarbonate is left; a similar decomposition taking place when the sesquicarbonate is exposed to air. Ammonia gas passed into a strong aqueous solution of the sesquicarbonate 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 passes back to ammonium bicarbonate.
Ammonium bicarbonate can also be formed by passing carbon dioxide through a solution of the normal compound, when it is deposited as a white powder, which has no smell and is only slightly soluble in water. The aqueous solution of this salt liberates carbon dioxide on exposure to air or on heating, and becomes alkaline in reaction. The aqueous solutions of all the carbonates when boiled undergo decomposition with liberation of carbon dioxide and the substance with which the carbonate ion reacted to form the bicarbonate, in this case, ammonia:
- NH4HCO3 → NH3 + H2O + CO2.
At room temperature, ammonium bicarbonate is a white, crystalline powder with a slight odor of ammonia that can dissolve in water to give a mildly alkaline solution. It is insoluble in acetone and alcohols. Ammonium bicarbonate decomposes at 36 to 60 °C into ammonia, carbon dioxide, and water vapor in an endothermic process (as it is with many ammonium salts) and so causes a drop in the temperature of the water. When reacted with acids, carbon dioxide is produced, while reactions with alkalis produce ammonia.
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 to home bakers. 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  (e.g., NO: “hjortetakksalt”, “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. 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 which 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 because of its relatively low quality and instability. 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.
It is also used for buffering solutions to slightly alkaline pH during chemical purification, such as HPLC. Because it entirely decomposes to volatile compounds this allows rapid recovery of the compound of interest by freeze-drying.
Ammonium bicarbonate decomposes to carbon dioxide, ammonia, and water vapor on heating; it liberates CO2 when treated with dilute mineral acids:
- NH4HCO3 + HCl → NH4Cl + CO2 + H2O.
It reacts with sulfates of alkaline-earth metals precipitating out their carbonates:
It also reacts with alkali metal halides, giving alkali metal bicarbonate and ammonium halide:
Ammonium bicarbonate is an irritant to the skin, eyes and respiratory system. Ammonium bicarbonate from China used to make cookies was found to be contaminated with melamine, and imports banned in Malaysia in the 2008 Chinese milk scandal.
- ^ a b c Online Sigma Catalogue , accessdate: June 8, 2011.
- ^ "separation of hornsalt". http://www.studenttorget.no/index.php?artikkelid=849.
- ^ ""separation of hornsalt" translated into English". http://www.tranexp.com:2000/InterTran?type=url&url=http%3A%2F%2Fwww.studenttorget.no%2Findex.php%3Fartikkelid%3D849&text=&from=nor&to=eng.
- ^ "What is hartshorn?". http://www.ochef.com/539.htm. Retrieved 2007-03-19.
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