Carbonic Acid (H2CO3)

Carbonic Acid is an inorganic, weak, and unstable acid. The molecule of Carbonic Acid consists of one carbon atom, two hydrogen atoms, and three oxygen atoms. Carbonic Acid is also referred to as a respiratory acid as it is the only acid that is exhaled in the gaseous state by human lungs.

Carbonic acid is studied majorly in various fields of science because of its vast applications and uses. It helps improve marine life due to its natural process of ocean acidification. It is essential for the human body as well. Further in this article, we will learn more about carbonic acids, their structure, their properties, and their uses.

What is Carbonic Acid?

Carbonic acid is a chemical compound made of carbon dioxide, oxygen, and hydrogen as its elements. It is a weak acid with the chemical formula H₂CO₃. It is formed when carbon dioxide is dissolved in water. Carbonic acid is a diprotic acid, which means it can form two types of salts: carbonate and bicarbonate. Carbonic Acid is also known as dihydrogen carbonate (because it is made of two hydrogen atoms and a carbonate ion), aerial acid (or acid of air), Oxidocarboxylic acid, Hydroxyformic acid, etc.

It was discovered by the French chemist Antoine Lavoisier in the late 18th century. He found that when carbon dioxide reacts with water an acidic solution is formed which he named as carbonic acid.

Formula of Carbonic Acid

Chemical formula of Carbonic acid is H₂CO₃

The compound of carbonic acid consists of one carbon atom, two hydrogen atoms, and three oxygen atoms. It can also be represented as OC(OH)₂ due to the presence of a carbon-oxygen double bond.

Structure of Carbonic Acid

Carbonic acid consists of a carboxyl functional group along with a hydroxyl group. The structure of carbonic acids consists of one carbon-oxygen double bond and further, this carbon is single bonded with two hydroxyl groups (OH). The structure of carbonic acid is shown below:

Carbonic Acid Lewis Structure

In the Lewis structure, the bonded electrons are shown with a solid line, and non-bonded electrons are shown with the dots. The structure of carbonic acid consists of one carbon atom, two hydrogen atoms, and three oxygen atoms. The Lewis structure of Carbonic Acid is shown below:

Here, each oxygen atom has 2 lone pairs, and the rest of the other electrons of each atom are bonded.

Preparation of Carbonic Acid

When strong acid reacts with calcium carbonate, carbon dioxide gas is evolved which when dissolved in water, Carbonic acid is formed. When carbon dioxide reacts with water molecules the following reaction takes place:

CO₂ (carbon dioxde ) + H₂O (water ) → H₂CO₃ (carbonic acid)

However, this reaction is reversible under suitable conditions. Also being a weak and unstable acid it can quickly dissociate into bicarbonate ions (HCO₃^–) and hydrogen ions (H⁺).

Properties of Carbonic Acid

Carbonic acid has a variety of properties which are classified into physical and chemical properties. The physical and chemical properties of carbonic acid are described below:

Physical Properties of Carbonic Acid

• State: Carbonic Acid generally occurs as a solution, but according to recent research it was found that Carbonic acid is also being prepared in a solid state by NASA scientists.
• Odor: Carbonic Acid are generally odorless.
• pKa value: The pKa value of Carbonic acid is 6.35. The pKa value is inversely proportional to the acidity of the compound. Hence, carbonic acid is termed under weak acid.
• Boiling Point: The boiling point of carbonic acid is around 127° Celsius.
• Melting Point: The melting point of carbonic acid is around -53° Celsius.
• Density: Carbonic acid has a density of around 1.668 grams per cubic centimeter.
• Molecular weight: The molecular weight of Carbonic acid is 62.024 g/mol.
• Conjugate base: The conjugate bases of Carbonic acid are bicarbonate and carbonate.

Chemical Properties of Carbonic Acid

• Stability: Carbonic acids are unstable under normal circumstances. However, they can be stabilized under high pressure and high temperatures.
• pH: Being a weak acidic, carbonic acid has a pH value of around 4.68
• Diprotic acid: It is a diprotic acid, i.e. it can form two types of salts namely carbonate and bicarbonate.
• Dissociation reaction: In the presence of water, Carbonic acid can partially dissociate into bicarbonate ions (HCO₃^–) and hydrogen ions (H⁺).
• Reaction with base: Carbonic acids form bicarbonate salt when reacted with a moderate amount of base and it form carbonate salts if reacted with excess amount of base.
• Decomposition reaction: Carbonic acid can easily decompose into carbon dioxide and water. However, this reaction is reversible under suitable conditions.

Acidity of Carbonic Acid

The acidity of an acid depends upon its pH and pKa value. The pKa value of carbonic acid is 6.35, and the pKa value of a compound is inversely proportional to the acidity of the compound. Hence, carbonic acid having a high pKa value is termed under weak acid. Also, the pH range of carbonic acid is 4.68 for 1 mmol/L, 4.18 for 10 mmol/L, and 3.68 for 100 mmol/L, which also shows that carbonic acids are moderately weak acids.

Uses of Carbonic Acid

• Carbonated Drinks: Carbonic acid provides the fizzy and bubbly taste in carbonated drinks like sparkling water, sodas, soft drinks, beer, champagne and other carbonated beverages
• Buffering System: Carbonic acid acts as a buffer system in human bodies which helps in maintaining the pH balance in the blood.
• pH regulation: Carbonic acid is also useful in regulating the pH level of water in swimming pools and in regulating pH balance in various other industrial processes.
• Medicinal uses: It is used in medications to balance acid-base levels in the body and in ointments to treat various fungal infections like ringworm. It is also consumed to induce vomiting (when required).
• pH indicator: Carbonic acid is used as a pH indicator to check whether the solution is acidic or basic.
• Precipitation: Carbonic acid is used as a solvent in the precipitation of various ammonium salts like ammonium persulfate.
• Cleansing agent: Carbonic acid is also used as a cleaning agent to clean contact lenses.

Carbonic Acid – FAQs

1. What is Carbonic Acid?

Carbonic acid is a chemical compound with carbondioxide, oxygen, and hydrogen as its elements. It is a weak acid with chemical formula H₂CO₃. It is formed when carbndioxide is disolved in water.

2. What is the Molar Mass of Carbonic Acid?

The molar mass of carbonic acid is 62.024 g/mol.

3. Is Carbonic Acid harmful to humans?

Being an acid, it is toxic and corrosive in nature but it is benificial for humans as it helps to maintain pH level of blood, helps in circulation of carbon dioxide and to maintain acid-base level in the body.

4. What is the importance of Carbonic Acid in Oceans?

Carbonic acid is formed in oceans when carbondioxide from the atmosphere is dissolved in ocean and reacts with water. This process is known as ocean acidification. It helps in maintaing health and sustainability of marine creatures.

5. What are the uses of Carbonic Acid?

Carbonic acid has a wide variety of usage, it is used in manufacturaing of various carbonated drinks, regulation of pH level in various substances, in balancing acid-base levels in the body, etc.

6. What is the importance of Carbonic Acid in the blood?

Carbonic acid is very important for our blood as :

• It helps in the process of respiratory gas exchange. It helps in transporting carbondioxide out of the body via blood cells.
• It acts a buffer system and maintains pH level of the blood.
• It balances the acid-base level in our blood. It dissociates into bicarbonate and hydrogen ions if there is excess amount of acid in the blood.

7. Is Carbonic Acid a Strong or a Weak Acid?

The pKa value of a compound is inversely proportional to the acidity of the compound. Hence, carbonic acid having a high pKa value (6.35) is termed under weak acid.

8. What is the pH value of Carbonic Acid?

At STP, Carbonic acid has a pH value of around 4.68 for 1 mmol/L, 4.18 for 10 mmol/L and 3.68 for 100 mmol/L.

9. What is pka of Carbonic Acid?

The pKa value of Carbonic acid is 6.35. It is reponsible for the acidic behaviour of carbonic acid.

10. What is Carbonic Acid Bicarbonate System?

Carbonic acid bicarbonate system acts as a buffer system in human bodies which helps in maintaining the pH balance in the blood. It also neutralize gastric acid in human bodies.

11. What happens when Citric Acid and Carbonic Acid react?

Citric acid and carbonic acid both are weak acids, Hence no reaction takes place between them.