What is Carbonic Acid?
Carbonic acid can be defined as a carbon-containing compound having the chemical formula H2CO3. The carbon dioxide solutions in water comprise small amounts of this compound. The carbonic acid's chemical formula can also be written as OC(OH)2 because, in this compound, there is one carbon-oxygen double bond.
Carbonic acid can often be described as a respiratory acid due to the reason it is the only acid exhaled by the human lungs in the gaseous state. It forms bicarbonate and carbonate salts, and it is a weak acid.
Note: H2CO3 is capable of dissolving limestone, which leads to the calcium bicarbonate (Ca(HCO3)2 formation. This is the primary reason for various features of limestone, including stalactites and stalagmites.
The carbonic acid or H2CO3 structure can be illustrated below.
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From the illustration above, we can understand that the carbonic acid structure consists of one carbon-oxygen double bond and two carbon-oxygen single bonds. The oxygen atoms that participate in a single bond with the carbon each contain one hydrogen atom attached to them.
Carbonic acid, formed by the hydrolysis and dissolution of CO2 in water, is the primary natural leaching agent in various temperate ecosystems. Carbonic acid is both unstable, weak and dissociates quickly into the bicarbonate ions (HCO3–) and hydrogen ions (H+).
When CO2 is dissolved in water, it participates in the chemical equilibrium as given below.
CO2 + H2O ⇌ H2CO3
However, in the chemical equilibrium described above, only a small amount of carbon dioxide is converted into carbonic acid.
Properties of H2CO3
A few major physical and chemical properties of carbonic acid are listed in this subsection:
The carbonic acid molar mass can be given as 62.024 grams per mole.
The H2CO3 compound holds a pKa value of 3.6.
It has a density of 1.668 grams per cubic centimetre in a standard state.
Generally, this compound exists as a solution. But, there has been reported that NASA scientists have prepared solid H2CO3 samples.
The conjugate base corresponding to the carbonic acid is bicarbonate.
H2CO3 is unstable in nature, and it is a weak acid.
In the presence of water, it undergoes partial dissociation to yield HCO3– (bicarbonate) and H+ ions.
Carbonic acid is a diprotic acid, and hence, it can form two types of salts: carbonates and bicarbonates.
Adding a small quantity of base to H2CO3 yields bicarbonate salts, whereas the addition of a base in excess amount yields carbonate salts.
It should also note that carbonic acid can be obtained as the burning of fossil fuels at an industrial scale or a by-product of industrial fermentation processes.
Carbonic Acid Uses
H2CO3 is an essential compound with a wide range of applications. A few of the carbonic acid uses are listed below:
The preparation of sparkling wine, carbonated water, and other aerated drinks involves carbonic acid use.
H2CO3 can be used in the precipitation of various ammonium salts like ammonium persulfate.
It helps in carbon dioxide transportation out of the body.
H2CO3 protonates many bases that contain nitrogen in blood serum
Ringworm and other dermatitides are treated through the carbonic acid application over the affected area.
Solutions that contain this compound are much effective in contact lens cleaning.
It can be orally consumed to induce vomiting whenever required (such as, in the case of a drug overdose).
Carbonic Acid Importance in Blood
The bicarbonate ion or molecule is an intermediate for the carbon dioxide transportation out of the human body through the respiratory gas exchange process. The hydration reactions undergone by carbon dioxide are very slow, especially in the absence of a suitable catalyst. The presence of the enzyme family called carbonic anhydrases in the red blood cells will result in an increase in reaction rate.
The carbonic anhydrase enzymes' enzymes work to catalyze the conversion of water and carbon dioxide into dissociated carbonic acid ions. This forms the bicarbonate anions that get dissolved in the plasma of the blood. This catalyzed reaction will get reversed in the lungs, resulting in CO2 formation, and then exhaled.
A Comment on the Carbonic Acid's Acidity
Carbonic acid is described as a carboxylic acid which holds a substituted hydroxyl group. It is also called polyprotic acid. Actually, this compound is diprotic and, hence, it has two protons which dissociate from the primary parent molecule. Thus, two dissociation constants exist, where the first one is for the dissociation into the bicarbonate ion.