Carbonic Acid: Formation, Structure & Chemical Equation

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  • 0:01 What Is Carbonic Acid?
  • 1:36 Chemical Structure
  • 2:38 How It's Formed
  • 5:01 Lesson Summary
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Lesson Transcript
Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

Did you know your favorite soda contains small amounts of a chemical called carbonic acid? It sure does! Continue reading to explore carbonic acid's formation and chemical structure.

What Is Carbonic Acid?

In relatively small amounts, carbonic acid is a chemical that can be found in sources such as human blood, carbonated beverages, and even rainwater. A chemical frequently appearing in a wide variety of places, you may be wondering…what is carbonic acid?

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. But first, how about we take a look at its chemical structure?

Chemical Structure

The chemical formula for carbonic acid is H2CO3. Its 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.

So it would make sense to call carbonic acid a type of organic acid, right? Well, did you know there's a lot of debate regarding this title? Some scientists believe carbonic acid is, without a doubt, an inorganic acid. As we'll see shortly, carbonic acid is formed from inorganic compounds, hence the big debate. Whether you decide to call carbonic acid an organic acid, inorganic acid, or name it after your best friend, that's certainly your call. Just make sure you know how to identify its chemical structure and formula.

How It's Formed

This is the part we've all been waiting for; how in the world is carbonic acid formed? Would you be shocked if you found out all you need is some water and carbon dioxide gas? This is certainly one way, perhaps the most common way, carbonic acid is formed. Now, keep in mind that the production of carbonic acid in nature is often spontaneous and in small amounts. No need to panic; carbonic acid isn't randomly floating around in our air. However, through the combination of water and carbon dioxide in the atmosphere, carbonic acid can be formed. This actually explains why we may find small amounts of this acid in rainwater. The following equation shows how carbonic acid is made via this reaction:

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