Carbonated beverages contain an acidic molecule called carbonic acid that decomposes when you open a bottle or can of a fizzy drink. The decomposition of carbonic acid produces the characteristic soda fizz. Despite its acidic properties, there's no evidence to suggest that carbonic acid in beverages does you any harm.
The compound carbonic acid has the chemical formula H2CO3. It's formed through the chemical reaction of carbon dioxide and water, and when it decomposes, it produces these as the products. Decomposition isn't the only chemical reaction carbonic acid can undergo; it can also act as an acid, and break into a positively charged hydrogen particle and a negatively charged HCO3, or bicarbonate, particle, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry." Circumstances help dictate which reaction carbonic acid undergoes.
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Carbonic acid dissolves in water, which is why it's possible to add it to beverages. In a sealed container, the carbonic acid tends to act like an acid, breaking into hydrogen and bicarbonate. Once you open a beverage container, however, any hydrogen and bicarbonate in the beverage quickly recombines to form carbonic acid, which then decomposes into water and carbon dioxide. The carbon dioxide bubbles up out of the beverage, releasing the gas into the air.
Bathing the teeth in acid isn't good for your dental enamel, and can lead to cavities. However, carbonic acid isn't particularly acidic compared to many of the other acids you'll find in sodas -- phosphoric acid, for instance -- and isn't implicated in damage to teeth, explains Dr. P. Moynihan in a 2002 article in the "British Dental Journal." This is partly because carbonic acid is relatively weak, and partly because it decomposes so quickly.
There aren't major health implications associated with consuming carbonic acid, both because it's a relatively weak acid and because it decomposes so quickly. However, the carbonic acid in soda and other fizzy beverages, as it breaks down, can lead to a buildup of air in the stomach. This can cause an uncomfortable bloating sensation, and may lead to burping. If you find these symptoms bothersome, you may wish to avoid carbonated beverages.