Did apart while others don’t. A partial dissociation

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.

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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:

Do you notice the double arrows in this equation? Think back to when we discussed equilibrium in regards to weak acids. This is a perfect example of equilibrium in action with a weak acid. By existing in equilibrium, carbonic acid can readily dissociate back to carbon dioxide and water. Carbon dioxide and water can freely combine to form carbonic acid.

This makes sense, as in nature things are not static. Molecules are constantly being formed and dissociated based on factors such as weathering, atmospheric, and environmental conditions.Now, we must talk about this concept of carbonic acid present in our carbonated drinks. How is it that this weak acid can be found in our Coke or Sprite? In order to make soda, carbon dioxide must dissolve in water producing small amounts of carbonic acid. It’s this acid, along with other acids such as phosphoric acid, that gives certain soda its tart taste. The acidic nature of carbonic acid also gives soda that fizz allowing us to freely burp away.

But wait a minute, this reaction of dissolving carbon dioxide in water sounds familiar. Actually, this is the same process we discussed earlier regarding carbonic acid’s presence in the atmosphere. This equilibrium state of carbonic acid dissociating to produce carbon dioxide and water, or combining carbon dioxide and water to make carbonic acid, is an important reaction involved in the formation of carbonic acid. The next time you guzzle that soda or get caught walking through a rain storm, think about the chemical reaction used to secure carbonic acid’s presence in those sources.

Lesson Summary

Let’s review. Carbonic acid is a type of weak acid formed from the dissolving of carbon dioxide in water. The chemical formula of carbonic acid is H2CO3.

Its structure consists of a carboxyl group with two hydroxyl groups connected. As a weak acid, it partially ionizes, dissociates or rather, breaks apart, in a solution. The molecules used to form carbonic acid, from dissociation and recombination, are in a constant state of equilibrium.

Carbonic acid is found in a variety of sources such as carbonated beverages and rainwater.


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