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CARBONIC ACID

CAS NUMBER: 463-79-6

EC NUMBER: 610-295-3

MOLECULAR FORMULA: CH2O3 (H2CO3)

MOLECULAR WEIGHT: 62.025

IUPAC NAME: carbonic acid

Carbonic Acid is a compound of the elements hydrogen, carbon, and oxygen. 
Carbonic Acid is formed in small amounts when its anhydride, carbon dioxide (CO2), dissolves in water.
In chemistry, Carbonic Acid is a dibasic acid with the chemical formula H2CO3. 
The pure compound decomposes at temperatures greater than ca. −80 °C.
In biochemistry and physiology, the name "carbonic acid" is often applied to aqueous solutions of carbon dioxide, which play an important role in the bicarbonate buffer system, used to maintain acid–base homeostasis

In aqueous solution Carbonic Acid behaves as a dibasic acid. 
The Bjerrum plot shows typical equilibrium concentrations, in solution, in seawater, of carbon dioxide and the various species derived from it, as a function of pH.
The acidification of natural waters is caused by the increasing concentration of carbon dioxide in the atmosphere, which is caused by the burning of increasing amounts of coal and hydrocarbons.

Expected change refers to predicted effect of continued ocean acidification.
Carbonic Acid has been estimated that the increase in dissolved carbon dioxide has caused the ocean's average surface pH to decrease by about 0.1 from pre-industrial levels.
The stability constants database contains 136 entries with values for the overall protonation constants, β1 and β2, of the carbonate ion. 

In Non-Biological Solutions:
The hydration equilibrium constant at 25 °C is called Kh, which in the case of carbonic acid is [H2CO3]/[CO2] ≈ 1.7×10−3 in pure water[9] and ≈ 1.2×10−3 in seawater.
Hence, the majority of the carbon dioxide is not converted into carbonic acid, remaining as CO2 molecules. 
In the absence of a catalyst, the equilibrium is reached quite slowly. 
The rate constants are 0.039 s−1 for the forward reaction and 23 s−1 for the reverse reaction.

In nature, limestone may react with rainwater, forming a solution of calcium bicarbonate; evaporation of such a solution will result re-formation of solid calcium carbonate. 
These processes occur in the formation of stalactites and stalagmites.

Use Of The term Carbonic Acid:
Strictly speaking the term "carbonic acid" refers to the chemical compound with the formula H2CO3.
Since pKa1 has a value of ca. 6.8 , at equilibrium carbonic acid will be almost 50% dissociated in the extracellular fluid (cytosol) which has a pH of ca.7.2. Note that dissolved carbon dioxide in extracellular fluid is often called as "carbonic acid" in biochemistry literature, for historical reasons. 
The reaction in which it is produced HCO3− + H+ ⇌ CO2 + H2O is fast in biological systems. 
Carbon dioxide can be described as the anhydride of carbonic acid.

Pure Carbonic Acid:
Carbonic acid, H2CO3, is stable at ambient temperatures in strictly anhydrous conditions. 
Carbonic Acid decomposes to form carbon dioxide in the presence of any water molecules.
Carbonic acid forms as a by-product of CO2/H2O irradiation, in addition to carbon monoxide and radical species (HCO and CO3).
Another route to form carbonic acid is protonation of bicarbonates (HCO3−) with aqueous HCl or HBr. 
This has to be done at cryogenic conditions to avoid immediate decomposition of H2CO3 to CO2 and H2O.

Amorphous H2CO3 forms above 120 K, and crystallization takes place above 200 K to give "β-H2CO3", as determined by infrared spectroscopy. 
The spectrum of β-H2CO3 agrees very well with the by-product after CO2/H2O irradiation.
β-H2CO3 sublimes at 230–260 K largely without decomposition. 
Matrix-isolation infrared spectroscopy allows for the recording of single molecules of H2CO3.

The fact that the carbonic acid may form by irradiating a solid H2O + CO2 mixture or even by proton-implantation of dry ice alone has given rise to suggestions that H2CO3 might be found in outer space or on Mars, where frozen ices of H2O and CO2 are found, as well as cosmic rays.
The surprising stability of sublimed H2CO3 up to rather high-temperatures of 260 K even allows for gas-phase H2CO3, e.g., above the pole caps of Mars.
Ab initio calculations showed that a single molecule of water catalyzes the decomposition of a gas-phase carbonic acid molecule to carbon dioxide and water. 
In the absence of water, the dissociation of gaseous carbonic acid is predicted to be very slow, with a half-life in the gas-phase of 180,000 years at 300 K.
This only applies if the molecules are few and far apart, because it has also been predicted that gas-phase carbonic acid will catalyze its own decomposition by forming dimers, which then break apart into two molecules each of water and carbon dioxide.

Solid "α-carbonic acid" was claimed to be generated by a cryogenic reaction of potassium bicarbonate and a solution of HCl in methanol.
This claim was disputed in a PhD thesis submitted in January 2014.
Instead, isotope labeling experiments point to the involvement of carbonic acid monomethyl ester (CAME). 
Furthermore, the sublimed solid was suggested to contain CAME monomers and dimers, not H2CO3 monomers and dimers as previously claimed.
Subsequent matrix-isolation infrared spectra confirmed that CAME rather than carbonic acid is found in the gas-phase above "α-carbonic acid".
The assignment as CAME is further corroborated by matrix-isolation of the substance prepared in gas-phase by pyrolysis.

At High Pressure:
Although molecules of H2CO3 do not constitute a significant portion of the dissolved carbon in aqueous "carbonic acid" under ambient conditions, significant amounts of molecular H2CO3 can exist in aqueous solutions subjected to pressures of multiple gigapascals (tens of thousands of atmospheres), such as can occur in planetary interiors.
Carbonic Acid should be stabilized under pressures of 0.6–1.6 GPa at 100 K, and 0.75–1.75 GPa at 300 K. 
These pressures are attained in the cores of large icy satellites such as Ganymede, Callisto, and Titan, where water and carbon dioxide are present. 
Pure carbonic acid, being denser, would then sink under the ice layers and separate them from the rocky cores of these moons

Despite Carbonic Acid's complicated history, carbonic acid may still appear as distinct polymorphs. 
Carbonic Acid forms upon oxidization of CO with OH-radicals.
Carbonic Acid is not clear whether carbonic acid prepared in this way needs to be considered as γ-H2CO3. 
The structures of β-H2CO3 and γ-H2CO3 have not been characterized crystallographically.

Carbonic Acid plays a role in the assembly of caves and cave formations like stalactites and stalagmites. 
The largest and most common caves are those formed by dissolution of limestone or dolomite by the action of water rich in carbonic acid derived from recent rainfall. 
The calcite in stalactites and stalagmites is derived from the overlying limestone near the bedrock/soil interface. 
Rainwater infiltrating through the soil absorbs carbon dioxide from the carbon dioxide-rich soil and forms a dilute solution of carbonic acid. 
When this acid water reaches the base of the soil, it reacts with the calcite in the limestone bedrock and takes some of it into solution. 
The water continues its downward course through narrow joints and fractures in the unsaturated zone with little further chemical reaction. 
When the water emerges from the cave roof, carbon dioxide is lost into the cave atmosphere, and some of the calcium carbonate is precipitated. 
The infiltrating water acts as a calcite pump, removing it from the top of the bedrock and redepositing it in the cave below.

Carbonic Acid is important in the transport of carbon dioxide in the blood. 
Carbon dioxide enters blood in the tissues because its local partial pressure is greater than its partial pressure in blood flowing through the tissues. 
As carbon dioxide enters the blood, it combines with water to form carbonic acid, which dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). 
Blood acidity is minimally affected by the released hydrogen ions because blood proteins, especially hemoglobin, are effective buffering agents. 

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 cell, catalyzes this reaction with sufficient rapidity that it is accomplished in only a fraction of a second. 
Because the enzyme is present only inside the red blood cell, bicarbonate accumulates to a much greater extent within the red cell than in the plasma. 
The capacity of blood to carry carbon dioxide as bicarbonate is enhanced by an ion transport system inside 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 the chloride shift, permits the plasma to be used as a storage site for bicarbonate without changing the electrical charge of either the plasma or the red blood cell. 
Only 26 percent of the total carbon dioxide content of blood exists as bicarbonate inside the red blood cell, while 62 percent exists as bicarbonate in plasma; however, the bulk of bicarbonate ions is first produced inside the cell, then transported to the plasma. 
A reverse sequence of reactions occurs when blood reaches the lung, where the partial pressure of carbon dioxide is lower than in the blood.

Carbonic Acid is a carbon-containing compound which has the chemical formula H2CO3. 
Solutions of carbon dioxide in water contain small amounts of this compound. 
Carbonic Acid's chemical formula can also be written as OC(OH)2 since there exists one carbon-oxygen double bond in this compound.

Carbonic Acid is often described as a respiratory acid since it is the only acid that is exhaled in the gaseous state by the human lungs. 
Carbonic Acid is a weak acid and it forms carbonate and bicarbonate salts.
H2CO3 can dissolve limestone, which leads to the formation of calcium bicarbonate (Ca(HCO3)2. 
This is the reason for many features of limestone, such as stalagmites and stalactites.

Preparations of Carbonic Acid:
From the illustration provided above, it can be understood that the structure of carbonic acid consists of one carbon-oxygen double bond and two carbon-oxygen single bonds. 
The oxygen atoms participating in a single bond with the carbon each have one hydrogen atom attached to them.

Carbonic Acid, which is formed by the dissolution and hydrolysis of CO2 in water, is the major natural leaching agent in many temperate ecosystems.  
Carbonic Acid is both weak and unstable and quickly dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3–)
Carbon dioxide, when dissolved in water, participates in the following chemical equilibrium:
CO2 + H2O ⇌ H2CO3
However, only a small amount of carbon dioxide is converted into carbonic acid in the chemical equilibrium described above.

Physical Properties:
-The molar mass of carbonic acid is 62.024 grams per mole.
-Carbonic Acid's density in its standard state is 1.668 grams per cubic centimetre.
-The compound H2CO3 has a pKa value of 6.35.
-The conjugate base corresponding to carbonic acid is the bicarbonate.
-This compound generally exists as a solution. However, it has been reported that solid H2CO3 samples have been prepared by NASA scientists.

Chemical Properties:
-H2CO3 is a weak acid and is unstable in nature.
-Carbonic Acid undergoes partial dissociation in the presence of water to yield H+ and HCO3– (bicarbonate) ions.
-Carbonic Acid is a diprotic acid, and can hence form two types of salts, namely bicarbonates and carbonates.
-Addition of a small quantity of a base to H2CO3 yields bicarbonate salts whereas addition of a base in excess yields carbonate salts.
Carbonic Acid can be noted that carbonic acid can be obtained as a by-product of industrial fermentation processes or the burning of fossil fuels at an industrial scale.

Uses of Carbonic Acid:
H2CO3 is a very important compound with a wide range of applications. 
Some of these uses of Carbonic Acid are listed below.

-The preparation of carbonated water, sparkling wine, and other aerated drinks involve the use of carbonic acid.
-Carbonic Acid is used in the precipitation of many ammonium salts such as ammonium persulfate.
-Carbonic Acid helps in the transportation of carbon dioxide out of the body.
-Various bases containing nitrogen in blood serum are protonated by H2CO3
-Ringworm and other dermatitides are treated via the application of carbonic acid over the affected area.
-Solutions containing this compound are very effective in the cleaning of contact lenses.
-Carbonic Acid can be consumed orally in order to induce vomiting whenever required (such as in drug overdose cases).
-The most common use of carbonic acid is in the form of salts.
-In blood: Bicarbonate a form of carbonic acid salt acts as an intermediate for transporting CO2 out of the body through the respiratory gas exchange. 
Carbonic Acid also plays a vital role in protonating a lot of nitrogen bases in blood serum. 
Carbonic acid is the main buffering element in the human body and is broken down into carbon dioxide by an enzyme called carbonic anhydrase. 
-In drinks: Carbonic acid is widely used in making bubbly, fizzy drinks.
-For treating dermatitides: it is typically used to treat dermatitides like ringworm.
-Carbonic Acid is also used as a mouthwash or for vaginal douche.
-In case of poisoning or drug overdose carbonic acid is given orally for inducing vomiting.
-For cleaning contact lenses carbonic acid is very effective, it is also used as a gas for welding, food processing, and cosmetics.

For hydrolysis of starch also carbonic acid is used.
Importance of Carbonic Acid in Blood:
The bicarbonate ion is known to be an intermediate for the transportation of carbon dioxide out the human body via the process of respiratory gas exchange. 
The hydration reactions undergone by carbon dioxide are quite slow, especially in the absence of a suitable catalyst. 
However, the presence of the enzyme family known as carbonic anhydrases in the red blood cells increases the reaction rate. 
The carbonic anhydrase enzymes work to catalyze the conversion of carbon dioxide and water to the dissociated ions of carbonic acid. 
This produces bicarbonate anions which get dissolved in the blood plasma. 
The catalyzed reaction is reversed in the lungs, resulting in the formation of CO2, which is then exhaled.

Importance of Carbonic Acid in Oceans:
The absorption of the excess carbon dioxide in the atmosphere (primarily due to human activities) by the oceans is believed to have caused a shift in the pH of the oceans water by approximately -0.1. 
The absorbed carbon dioxide reacts with ocean water and forms H2CO3. 
This process is commonly referred to as ocean acidification.

What are the uses of carbonic acid?
Carbonic Acid is widely used in the production of soft drinks, artificially carbonated sparkling wines, and other bubbly beverages. 
Carbonic Acid salts are called bicarbonates (or carbonates of hydrogen), and carbonates.

Comment on the acidity of carbonic acid:
Carbonic Acid is a carboxylic acid that holds a substituted hydroxyl group. 
Carbonic Acid is also a polyprotic acid. 
This compound is actually diprotic and, therefore, has two protons that dissociate from the primary parent molecule. 
Therefore, there are two constants of dissociation, of which the first one is for the dissociation into the bicarbonate ion.

What is the role of Carbonic Acid in blood?
Bicarbonate is an intermediate in the exchange of respiratory gas for conveying CO2 out of the body. 
In general, the hydration reaction of CO2 is very slow in the absence of a catalyst, but red blood cells contain a substance known as carbonic anhydrase, which increases the reaction rate, creating dissolved bicarbonate (HCO3−) in the blood plasma.

Is Carbonic Acid a strong acid?
No, carbonic acid is not a strong acid. 
H2CO3 is a weak acid that dissociates into a proton (H+ cation) and a bicarbonate ion (HCO3- anion). 
This compound only partly dissociates in aqueous solutions. 
Furthermore, the conjugate base of carbonic acid, which is the bicarbonate ion, is a relatively good base. 
These are the reasons why carbonic acid is classified as a weak acid rather than a strong acid.

Carbonic Acid is a weak dibasic acid H2CO3 known only in solution that reacts with bases to form carbonates.
Carbonic Acid is a carbon oxoacid and a chalcocarbonic acid. 
Carbonic Acid has a role as a mouse metabolite. 
Carbonic Acid is a conjugate acid of a hydrogencarbonate.
The hypothetical acid of carbon dioxide and water. 
Carbonic Acid exists only in the form of its salts (carbonates), acid salts (hydrogen carbonates), amines (carbamic acid), and acid chlorides (carbonyl chloride). 

Carbonic Acid is the cause of some cave formations. 
This happens when rainwater combines with carbon dioxide and forms carbonic acid, which reacts with the calcium in limestone and erodes it over time.
Just like carbonic acid can erode limestone, it also has the potential to corrode steel. 
Iron carbonate is formed when carbonic acid is brought into contact with some steels. 
Iron carbonate can cause a higher rate of iron loss from the base steel than would occur if the iron carbonate was not formed.

In relatively small amounts, carbonic acid is a chemical that can be found in sources such as human blood, carbonated beverages, and even rainwater. 
Carbonic acid is a weak acid that's formed from the reaction of carbon dioxide dissolved in water. 
Let's take a walk down memory lane and review the concept of weak acids. 
By definition, a weak acid is only partially ionized in a solution. 
In other words, weak acids don't completely dissociate, or break apart, into ions in a solution.

Using diagram 1 as an example (see video), let's say you decide to place acetic acid, an ingredient in vinegar, in water. 
Some molecules of acetic acid break apart while others don't. 
A partial dissociation in solution is occurring. 
Now, what encourages a weak acid to dissociate? 
Factors like the strength of a weak acid can influence this degree of dissociation.
One thing to remember with all weak acids, such as carbonic acid, is that there is a state of equilibrium between dissociation and recombination. 
Just as you saw those molecules of acetic acid break apart in solution at equilibrium, those same pieces can re-combine to form acetic acid molecules. 
This state of equilibrium between a weak acid dissociating and recombining is important when we talk about the formation of carbonic acid.

Chemical Structure:
The chemical formula for carbonic acid is H2CO3. 
Carbonic Acid's chemical structure is shown in diagram 2 (see video). 
You can see that this acid is composed of a carboxyl group (C=O) with two hydroxyl groups (OH) connected. 
Because there's a carbon atom present in this molecule, we can identify this as an organic compound. 
Since this molecule also has acidic properties, discussed earlier regarding weak acids, we can call this molecule an acid.

Carbonic Acid is a chemical compound with the chemical formula as H2CO3 and molecular formula as CH2O3. It is an inorganic weak acid, which exists only as a solution. 
Carbonic Acid is also known as acid of air, aerial acid or dihydrogen carbonate. 
Carbonic Acid forms two kinds of salts: carbonates and bicarbonates. 
Ph of carbonic acid is 4.68 in 1mM.

Carbonic Acid is specifically diprotic acid, which means that it has two protons which can disassociate from the parent molecule. 
Thus, have two disassociation constants, first for bicarbonate ion disassociation and second for disassociation of the bicarbonate ion into the carbonate ion.

OCCURRENCE:
Carbonic Acid is present in blood in the human body. 
Carbonic Acid is formed in the human body when water gets dissolved with carbon dioxide. 
Carbonic Acid is also present in: 
-rainwater
-calcite
-fermentation
-coal
-groundwater
-meteors
-volcanoes
-amino acids
-proteins
-oceans
-plants
-erythrocytes
-sulphur deposits
-salts
-caves

Hydrogen carbonate, also known as H2CO3 or [co(OH)2], belongs to the class of organic compounds known as organic carbonic acids. 
Organic carbonic acids are compounds comprising the carbonic acid functional group. 
Bicarbonate also acts to regulate pH in the small intestine. 
Hydrogen carbonate is a very weakly acidic compound (based on its pKa). 
A parallel example is sodium bisulfite (NaHSO3). 

Hydrogen carbonate exists in all living species, ranging from bacteria to humans. 
In humans, hydrogen carbonate is involved in the metabolic disorder called the hartnup disorder pathway. 
Outside of the human body, Hydrogen carbonate has been detected, but not quantified in, several different foods, such as lovages, lima beans, tree ferns, mountain yams, and burbots. 
This could make hydrogen carbonate a potential biomarker for the consumption of these foods. 
As such it is an important sink in the carbon cycle. 
Carbonic Acid is isoelectronic with nitric acid HNO3.

Carbonic Acid Belongs to the class of organic compounds known as organic carbonic acids. 
Organic carbonic acids are compounds comprising the carbonic acid functional group.

Substituents:    
-Carbonic acid
-Organic oxygen compound
-Organic oxide
-Hydrocarbon derivative
-Organooxygen compound
-Carbonyl group
-Aliphatic acyclic compound


PHYSICAL PROPERTIES OF CARBONIC ACID:

-Molecular Weight: 62.025    

-Exact Mass: 62.000393922    

-Monoisotopic Mass: 62.000393922    

-Topological Polar Surface Area: 57.5 Ų    

-Physical Description: Solid

-Color: colorless

-Melting Point: 720°C

-Solubility: Freely soluble in water/Insoluble in ethanol

-Solubility in water: 12.8 mg/mL

-Polar Surface Area: 57.53 Ų

-Water Solubility: 231 g/L

-logP: 0.6    

-logP: 0.25    

-logS: 0.57

-pKa (Strongest Acidic): 6.05

Carbonic Acid is an inorganic compound with the formula H2CO3. 
Carbonic Acid is comprised of water and carbon dioxide. 
Carbonic Acid has a molar mass of about 62 g/mol. 
Carbonic Acid, while relatively weak when compared with other acids, can cause corrosion depending on the chemical composition of the material. 
Carbonic Acid is one of the most common causes of low pH levels in water.

Carbonic Acid is a very common type of acid because of the abundance of carbon dioxide and water. 
Carbonic Acid is unique in that it is contains carbon but it is an inorganic compound.

Carbonic Acid is found in the blood stream. 
The carbon dioxide in blood bonds with the water in the blood. 
Carbonic Acid is also commonly used to carbonate beverages. 
Carbonic Acid has many other industrial uses as well.

CHEMICAL PROPERTIES OF CARBONIC ACID:

-XLogP3-AA: -0.1

-Hydrogen Bond Acceptor Count: 3    

-Rotatable Bond Count: 0    

-Heavy Atom Count: 4    

-Formal Charge: 0    

-Complexity: 26.3    

-Isotope Atom Count: 0    

-Defined Atom Stereocenter Count: 0    

-Undefined Atom Stereocenter Count: 0    

-Defined Bond Stereocenter Count: 0    

-Undefined Bond Stereocenter Count: 0

-Covalently-Bonded Unit Count: 1    

-Compound Is Canonicalized: Yes

-Refractivity: 9.5 m³·mol⁻¹

-Polarizability: 4.23 ų

STORAGE OF CARBONIC ACID:

-Carbonic Acid should be stored in plastic bottles.
-Carbonic Acid should be stored in a moisture-free environment.
-Carbonic Acid should be kept in ventilated environments.

-Carbonic Acid should be in dry and clean containers.
-Carbonic Acid should be stored under constant temperature.
-Carbonic Acid must be under constant pressure.

-Carbonic Acid Should be stored separately from strong bases.
-Carbonic Acid should be kept away from immediate reagents.

SYNONYMS:

Hydroxyformic acid
Hydroxymethanoic acid
Dihydroxycarbonyl
carbonic acid
hydroxy ketone
hydroxy-ketone
hydroxidodioxidocarbon(.)
Acidosan
Jusonin
Soludal
Meylon
Neut
component of Col-Evac
Crystol carbonate
Soda Ash
component of Pretts
Monosodium hydrogen carbonate
Dihydrogen carbonate
dihydroxyketone
hydroxyketone
Koehlensaeure
hydroxyl ketone
Carbonic acid-
hydrogen bicarbonate
hydrogencarbonic acid
dihydroxidooxidocarbon
hydroxycarboxylic acid
hydrogentrioxocarbonate

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