por What is ammonium carbonate?
He ammonium carbonate It is an inorganic salt of nitrogen, specifically ammoniacal, whose chemical formula is (NH4)2CO3. It is made using synthesis methods, among which the sublimation of a mixture of ammonium sulfate and calcium carbonate stands out: (NH4)2SO4(s) + CaCO3(s) => (NH4)2CO3(s) + CaSO4( s).
Generally, ammonium and calcium carbonate salts are heated in a pot to form ammonium carbonate. The industrial method that produces tons of this salt consists of passing carbon dioxide through an absorption column that contains a solution of ammonium in water, followed by distillation.
Vapors containing ammonium, carbon dioxide, and water condense to form ammonium carbonate crystals: 2NH3(g) + H2O(l) + CO2(g) → (NH4)2CO3(s). The reaction produces carbonic acid, H2CO3, after dissolving carbon dioxide in water, and it is this acid that gives up its two protons, H+, to two molecules of ammonia.
Ammonium Carbonate Properties
It is a colorless, crystalline, white solid with strong ammonia-like odors and flavors. It melts at 58 ºC decomposing into ammonia, water and carbon dioxide: exactly the previous chemical equation but in the opposite direction.
However, this decomposition occurs in two steps: first an NH3 molecule is released, producing ammonium bicarbonate (NH4HCO3); and second, if heating continues, the carbonate disproportionates, releasing even more gaseous ammonia.
It is a solid that is highly soluble in water and less soluble in alcohols. It forms hydrogen bonds with water, and when 5 grams is dissolved in 100 grams of water, it produces a basic solution with a pH around 8.6.
Its high affinity for water makes it a hygroscopic solid (absorbs moisture), and for this reason it is difficult to find it in its anhydrous form. In fact, its monohydrated form, (NH4)2CO3·H2O), is the most common of all and explains how salt carries ammonia gas, which causes odor.
In air it decomposes to generate ammonium bicarbonate and ammonium carbonate (NH4NH2CO2).
chemical structure
In the image above the chemical structure of ammonium carbonate is illustrated. In the middle is the CO32– anion, the flat triangle with the black center and the red spheres; and on both sides, the ammonium NH4+ cations with tetrahedral geometries.
The geometry of the ammonium ion is explained by the sp3 hybridization of the nitrogen atom, arranging the hydrogen atoms (the white spheres) around it in the form of a tetrahedron. Between the three ions interactions are established by hydrogen bonds (H3N-H— O-CO22–).
Thanks to its geometry, a single CO32– anion can form up to three hydrogen bonds; while NH4+ cations may not be able to form their corresponding four hydrogen bonds because of electrostatic repulsions between their positive charges.
The result of all these interactions is the crystallization of an orthorhombic system. Why is it so hygroscopic and soluble in water? The answer is in the same previous paragraph: hydrogen bonds.
It is these interactions that are responsible for the rapid absorption of water from the anhydrous salt to form (NH4)2CO3·H2O). This results in changes in the spatial arrangement of the ions, and consequently, in the crystalline structure.
structural curiosities
As simple as (NH4)2CO3 may appear, it is so sensitive to an infinite number of transformations that its structure is a mystery subject to the true composition of the solid. This structure also varies according to the pressures that impinge on the crystals.
Some authors have found that ions are arranged as coplanar chains linked by hydrogen bonds (ie, a chain with a sequence NH4+—CO32–—…) in which water molecules probably serve as linkers to other chains.
Even more, transcending the terrestrial sky, what are these crystals like in space or interstellar conditions? What are their compositions in terms of the stabilities of the carbonate species? There are studies that confirm the great stability of these crystals trapped in planetary ice masses and comets.
This allows them to act as reserves of carbon, nitrogen and hydrogen, which, receiving solar radiation, can be transformed into organic material such as amino acids.
In other words, these icy ammoniacal blocks could be carriers of «the wheel that starts the machinery of life» in the cosmos. For these reasons his interest in the field of astrobiology and biochemistry is growing.
Uses/applications
It is used as a leavening agent, since when heated it produces carbon dioxide and ammonium gases. Ammonium carbonate is, if you will, a precursor to modern baking powders and can be used to bake cookies and flatbreads.
However, its use is not recommended for baking cakes. Due to the thickness of the cakes, ammonium gases are trapped inside and produce an unpleasant taste.
It is used as an expectorant, that is, it relieves cough by decongesting the bronchi. It has fungicidal action, being used for this reason in agriculture. It is also a regulator of the acidity present in foods and is used in the organic synthesis of urea under high pressure conditions, and of hydantoins.
risks
Ammonium carbonate is highly toxic. It produces acute irritation of the oral cavity in humans upon contact.
Furthermore, if it is ingested it causes gastric irritation. A similar action is observed in eyes exposed to ammonium carbonate.
Inhalation of gases from salt decomposition can irritate the nose, throat and lungs, causing coughing and difficulty breathing.
Acute exposure of fasting dogs to ammonium carbonate at a dose of 40 mg/kg of weight causes vomiting and diarrhea. The highest doses of ammonium carbonate (200 mg/kg of weight) are usually lethal. Cardiac damage is indicated as the cause of death.
If heated to very high temperatures and in oxygen-enriched air, it gives off toxic NO2 gases.
References
PubChem. (2018). Ammonium Carbonate. Retrieved on March 25, 2018, from PubChem: pubchem.ncbi.nlm.nih.gov
Organic Chemistry Portal. ((2009-2018)). Bucherer-Bergs Reaction. Retrieved on March 25, 2018, from the Organic Chemistry Portal: www.organic-chemistry.org
Wikipedia. (2018). Ammonium carbonate. Retrieved on March 25, 2018, from Wikipedia: en.wikipedia.org
The Chemical Company. (2018). The Chemical Company. Retrieved on March 25, 2018, from The Chemical Company: thechemco.com