He carbonic acid , Formerly called air acid or air acid, is the only inorganic acid of carbon and has the formula H2CO3.
The salts of carbonic acids are called bicarbonates (or hydrogen carbonates) and carbonates (Human Metabolome Database, 2017). Its structure is presented in figure 1 (EMBL-EBI, 2016).
Figure 1: Structure of carbonic acid.
It is said that the carbonic acid is formed by carbon dioxide and water. Carbonic acid occurs only through salts (carbonates), acid salts (hydrogen carbonates), amines (carbamic acid) and acid chlorides (carbonyl chloride) (MeSH, 1991).
The compound can not be isolated as a pure or solid liquid, since the products of its decomposition, carbon dioxide and water, are much more stable than acid (Royal Society of Chemistry, 2015).
Carbon dioxide is found in the human body, the CO2 present in the blood is combined with water to form carbonic acid, which is then exhaled as a gas through the lungs.
It is also found in rocks and caves where limestones can be dissolved. H2CO3 can also be found in coal, meteorites, volcanoes, acid rain, groundwater, oceans and plants (Carbonic acid Formula, S.F.).
Carbonic acid and carbonate salts
Carbonic acid is formed in small amounts when its anhydride , Carbon dioxide (CO2), is dissolved in water.
CO2 + H2O ⇌ H2CO3
The predominant species are simply hydrated CO2 molecules. Carbonic acid may be considered to be a diprotic acid from which two series of salts can be formed, namely hydrogen carbonates, or bicarbonates, containing HCO 3 -, and CO 2 - containing carbonates.
H2CO3 + H2O ⇌ H3O + + HCO3-
HCO3- + H2O ⇌ H3O + + CO32-
However, the acid-base behavior of carbonic acid depends on the different velocities of some of the reactions involved, as well as its dependence on the pH of the system. For example, at a pH below 8, the major reactions and their relative velocity are as follows:
- CO2 + H2O ⇌ H2CO3 (slow)
- H2CO3 + OH- ⇌ HCO3- + H2O (fast)
Above pH 10 the following reactions are important:
- CO2 + OH- ⇌ HCO3- (slow)
- HCO3- + OH- ⇌ CO32- + H2O (fast)
Between pH values of 8 and 10, all previous equilibrium reactions are significant (Zumdahl, 2008).
"Hypothetical"acid of carbon dioxide and water
Until relatively recently, scientists were convinced that carbonic acid did not exist as a stable molecule.
In the journal Angewandte Chemie, German researchers have introduced a simple pyrolytic method for the production of carbonic acid in the gas phase that allowed the spectroscopic characterization of carbonic acid in the gas phase and its monomethyl ester (Angewandte Chemie International Edition, 2014).
Carbonic acid exists only for a small fraction of a second when carbon dioxide dissolves in water before being transformed into a mixture of protons and bicarbonate anions.
Despite its short life, however, carbonic acid imparts a lasting impact on the atmosphere and geology of the Earth as well as on the human body.
Due to its short shelf life, the detailed chemistry of carbonic acid has been obscured in the mystery. Researchers such as Berkeley Lab. And the University of California (UC) Berkeley are helping to lift this veil through a series of unique experiments.
In their latest study, they have demonstrated how gaseous carbon dioxide molecules are solvated by water to initiate proton transfer chemistry that produces carbonic acid and bicarbonate (Yarris, 2015).
In 1991 scientists at NASA's Goddard Space Flight Center (USA) were able to make solid samples of H2CO3. They did so by exposing a frozen mixture of water and carbon dioxide to high-energy proton radiation, and then heating it to remove excess water.
The remaining carbonic acid was characterized by infrared spectroscopy. The fact that carbonic acid has been prepared by irradiating a solid mixture of H2O + CO2, or even by dry ice irradiation alone.
This has led to suggestions that H2CO3 could be found in outer space or on Mars, where H2O and CO2 ices are found, as well as cosmic rays (Khanna, 1991).
Physical and chemical properties
Carbonic acid exists only in aqueous solution. The pure compound could not be isolated. Said solution is readily recognizable because it exhibits an effervescence of gaseous carbon dioxide escaping from the aqueous medium.
It has a molecular weight of 62.024 g / mol and a density of 1.668 g / ml. Carbonic acid is a weak and unstable acid, which partially dissociates in water in hydrogen ions (H +) and bicarbonate ions (HCO3-) whose pKa is 3,6.
Being a diprotic acid, it can form two types of salts, carbonates and bicarbonates. Addition of the base to an excess of carbonic acid gives bicarbonate salts, while addition of excess base to carbonic acid gives carbonate salts (National Center for Biotechnology Information, 2017).
Carbonic acid is not considered toxic or dangerous, and is present in the human body. However, exposure to high concentrations may irritate the eyes and respiratory tract.
Applications
According to Michelle McGuire Nutrition Sciences, and Carbonic acid is found in fermented foods in the form of waste generated by bacteria that are fed by decaying food.
The gas bubbles produced in foods are generally the carbon dioxide of carbonic acid and a sign that the food is fermenting. Examples of commonly eaten fermented foods are soy sauce, miso soup, sauerkraut, kimchi korean, tempeh, kefir and yogurt.
Fermented grains and vegetables also contain beneficial bacteria that can control potentially pathogenic microorganisms inside your intestines and improve the production of Vitamins B-12 Y K .
Carbonic acid, carbon dioxide solution or dihydrogen carbonate is formed during the process of Water carbonation . It is responsible for the effervescent aspect of soft drinks and soda, as stated in the Dictionary of Food Science and Technology.
Carbonic acid contributes to the high acidity of soda, but the content of refined sugar and phosphoric acid are mainly responsible for this acidity (DUBOIS, 2016).
Carbonic acid is also used in many other fields, such as pharmaceuticals, cosmetics, fertilizers, food processing, anesthetics, etc.
Importance
Carbonic acid is commonly found in the water of oceans, seas, lakes, rivers and rain because it forms when carbon dioxide, which is widespread in the atmosphere, comes into contact with water.
It is even present in glacial ice, although in smaller amounts. Carbonic acid is a very weak acid, although it can contribute to erosion over time.
The increase in carbon dioxide in the atmosphere has led to the generation of more carbonic acid in the oceans and is, to some extent, responsible for the slight increase in the acidity of the oceans during the last hundred years.
Carbon dioxide, a waste product of cellular metabolism, is in a relatively high concentration in tissues. It diffuses into the blood and is carried to the lungs to be removed with expired air.
Carbon dioxide is much more soluble than oxygen and diffuses easily into red blood cells. It reacts with water to form carbonic acid, which at the alkaline pH of the blood appears mainly as bicarbonate (Robert S. Schwartz, 2016).
Carbon dioxide enters the blood and tissues because its local partial pressure is greater than its partial pressure in the blood flowing through the tissues. As carbon dioxide enters the blood, it combines with water to form carbonic acid that dissociates into hydrogen ions (H +) and bicarbonate ions (HCO3-).
The natural conversion of carbon dioxide to carbonic acid is a relatively slow process. However, carbonic anhydrase, a protein enzyme present inside the red blood cells, catalyzes this reaction quickly enough so it is achieved in only a fraction of a second.
CO2 + H2O ⇌ H2CO3
Because the enzyme is present only inside the red blood cells, bicarbonate accumulates to a much greater extent within the red blood cells than in the plasma.
The ability of blood to transport carbon dioxide as bicarbonate is enhanced by an ion transport system within the red blood cell membrane that simultaneously moves a bicarbonate ion out of the cell and into the plasma in exchange for a chloride ion .
The simultaneous exchange of these two ions, known as chloride change, allows the plasma to be used as a bicarbonate storage site without changing the electric charge of the plasma or red blood cells.
Only 26 percent of the total carbon dioxide content of the blood exists as bicarbonate inside the red blood cells, while 62 percent exists as bicarbonate in plasma; However, most bicarbonate ions occur first within the cell, then transported to the plasma.
An inverse sequence of reactions occurs when blood reaches the lung, where the partial pressure of carbon dioxide is lower than in the blood. The reaction catalyzed by carbonic anhydrase is reversed in the lungs, where it converts bicarbonate to CO2 and allows its expulsion (Neil S. Cherniack, 2015).
References
- Angewandte Chemie International Edition. (2014, September 23). Carbonic Acid - And Yet It Exists! Retrieved from chemistryviews.org.
- Carbonic acid Formula. (S.F.). Recovered from softschools.com.
- DUBOIS, S. (2016, January 11). Carbonic Acid in Foods. Retrieved from livestrong.com.
- EMBL-EBI. (2016, January 27). Carbonic acid. Retrieved from ebi.ac.uk.
- Human Metabolome Database. (2017, March 2). Carbonic acid. Retrieved from hmdb.ca.
- Khanna, M. M. (1991). Infrared and mass spectral studies of proton irradiated H2O + CO2 ice: Evidence for carbonic acid. Spectrochimica Acta Part A: Molecular Spectroscopy Volume 47, Issue 2, 255-262. Retrieved from science.gsfc.nasa.gov.
- (1991). Carbonic Acid. Retrieved from ncbi.nlm.nih.
- National Center for Biotechnology Information. . (2017, March 11). PubChem Compound Database; CID = 767. Retrieved from pubchem.ncbi.nlm.nih.gov.
- Neil S. Cherniack, e. to. (2015, March 20). Human respiratory. Retrieved from britannica.com.
- Robert S. Schwartz, C.L. (2016, April 29). Blood. Retrieved from britannica.com.
- Royal Society of Chemistry. (2015). Carbonic acid. Retrieved from: chemspider.com.
- Yarris, L. (2015, June 16). Unraveling the Mysteries of Carbonic Acid. Retrieved from: newscenter.lbl.gov.
- Zumdahl, S. S. (2008, August 15). Oxyacid. Retrieved from: britannica.com.