Carbonic Acid - Structure, Importance, Properties & Uses, FAQs

Carbonic Acid Structure

Carbonic acid has a trigonal planar arrangement around the carbon atom.

$\mathrm{HO}-\mathrm{C}(=\mathrm{O})-\mathrm{OH}$

• Central atom: Carbon (C)
• Bonds:
• One double bond between carbon and oxygen ( $\mathrm{C}=\mathrm{O}$ )
• Two single bonds between carbon and hydroxyl groups (-OH)
• Hybridization of carbon: $s p^2$
• Bond angle: $\sim 120^{\circ}$
• Shape: Trigonal planar around carbon

Carbonic acid is unstable in free form and usually exists in equilibrium with carbon dioxide and water:

$\mathrm{H}_2 \mathrm{CO}_3 \rightleftharpoons \mathrm{CO}_2+\mathrm{H}_2 \mathrm{O}$

As demonstrated by the illustration above, carbonic acid has a structure that includes a carbon-oxygen double bond and two carbon-oxygen single bonds. One Hydrogen atom is attached to each oxygen atom participating in a single bond with the carbon.

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Carbonic Acid Properties

Under this subsection, you will find a list of some of the significant physical and chemical properties of carbonic acid.

1. Physical-Chemical Properties

• Carbonic acid has a molar mass of 62.024 grams per mole.
• 1.668 grams per cubic centimeter is its density in its standard state.
• In chemical terms, $\mathrm{H}_2 \mathrm{CO}_3$ has a p Ka of 6.35.
• As a conjugate base, bicarbonate corresponds to carbonic acid.
• In most cases, this compound is dissolved in water. There have been reports that NASA scientists have prepared solid $\mathrm{H}_2 \mathrm{CO}_3$ samples.

2. Chemical Properties

• A weak acid, $\mathrm{H}_2 \mathrm{CO}_3$ is inherently unstable in nature.
• When water is present, it dissociates partially to give H⁺ and $\mathrm{HCO}_3^{-}$ (bicarbonate) ions.
• A diprotic acid such as carbonic acid can form two types of salts, both of which are bicarbonates.
• Bicarbonate salts are formed by adding a small quantity of a base to $\mathrm{H}_2 \mathrm{CO}_3$, whereas carbonate salts are formed by adding an excess of a base.
• Interestingly, industrial fermentation processes or the burning of fossil fuels can result in the production of carbonic acid by-products.

Carbonic Acid Uses

With a wide range of uses, $\mathrm{H}_2 \mathrm{CO}_3$ is a very useful compound. Carbonic acid is also used in the following ways.

• It is carbonic acid that is used to prepare carbonated water, sparkling wine, and other aerated drinks.
• Ammonium persulfate is precipitated from $\mathrm{H}_2 \mathrm{CO}_3$ powder.
• By transporting carbon dioxide from the body, it helps to eliminate it.
• Ringworm and other dermatitis are treated by protonating certain nitrogenous bases in blood serum and applying a solution of carbonic acid to the area.
• Cleansing contact lenses with these solutions is extremely effective.
• When necessary (such as during drug overdoses), it can be consumed orally to induce vomiting.

Importance of Carbonic Acid in Oceans

oceans are believed to have shifted the pH of the ocean water by approximately 0.1 due to the absorption of excess carbon dioxide from the atmosphere (primarily caused by human activities). Ocean water reacts with carbon dioxide to form hydrogen carbonate. Ocean acidification is a common term used to describe this process.

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Some Solved Examples

Question 1: Carbonic acid exists in aqueous solution mainly due to:

A. Strong hydrogen bonding
B. High stability of $\mathrm{H}_2 \mathrm{CO}_3$
C. Equilibrium between $\mathrm{CO}_2$ and $\mathrm{H}_2 \mathrm{O}$
D. Complete ionization in water

Solution:

Carbonic acid is unstable and exists only in equilibrium:

$\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_2 \mathrm{CO}_3$
Hence, it survives only due to continuous formation from $\mathrm{CO}_2$ and water.

Hence, the correct answer is option (3)

Question 2: The hybridization and geometry of carbon atom in carbonic acid are:

A. $\mathrm{sp}^3$, tetrahedral
B. $\mathrm{sp}^2$, trigonal planar
C. sp, linear
D. $\mathrm{sp}^3$, pyramidal

Solution:

Carbon forms:

• One $\mathrm{C}=\mathrm{O}$ double bond
• Two C-O single bonds

Total $3 \sigma$ bonds $\rightarrow \mathrm{sp}^2$ hybridization, giving trigonal planar geometry.

Hence, the correct answer is option (2)

Question 3: Which of the following correctly represents the structure of carbonic acid?

A. $\mathrm{O}=\mathrm{C}(\mathrm{OH})_2$
B. $\mathrm{HO}-\mathrm{C} \equiv \mathrm{O}-\mathrm{OH}$
C. $\mathrm{HO}-\mathrm{C}(-\mathrm{OH})=\mathrm{O}$
D. $O-C(=O)-O$

Solution:

Carbonic acid structure is:

$\mathrm{HO}-\mathrm{C}(=\mathrm{O})-\mathrm{OH}$

Hence, the correct answer is option (1)

Question 4: Carbonic acid behaves as:

A. Monobasic acid
B. Dibasic acid
C. Tribasic acid
D. Neutral compound

Solution:

Carbonic acid has two replaceable hydrogen atoms, hence it is a dibasic (diprotic) acid:

$\mathrm{H}_2 \mathrm{CO}_3 \rightarrow \mathrm{HCO}_3^{-} \rightarrow \mathrm{CO}_3^{2-}$

Hence, the correct answer is option (2)