A very weak acid formed in solution when carbon dioxide dissolves in water.

A very weak acid formed in solution when carbon dioxide dissolves in water.

• A. Carbonic Acid
• B. Hydrochloric Acid
• C. Sulfuric Acid
• D. Nitric Acid

Answer: (A)

Dissolving carbon dioxide in water creates a weak acid called carbonic acid. When CO2 is in water, it reacts to form carbonic acid (CO2 + H2O ⇌ H2CO3). This carbonic acid only partly dissociates to release hydrogen ions (H+) (H2CO3 ⇌ H+ + HCO3−), so only a small amount of acidity appears in the solution. That partial ionization is what makes carbonic acid a weak acid. In contrast, the other acids listed are strong acids that dissociate almost completely in water, releasing many more hydrogen ions and making the solution much more acidic. They’re not formed simply by dissolving carbon dioxide in water, which is why carbonic acid is the correct choice.

Dissolving carbon dioxide in water creates a weak acid called carbonic acid. When CO2 is in water, it reacts to form carbonic acid (CO2 + H2O ⇌ H2CO3). This carbonic acid only partly dissociates to release hydrogen ions (H+) (H2CO3 ⇌ H+ + HCO3−), so only a small amount of acidity appears in the solution. That partial ionization is what makes carbonic acid a weak acid.

In contrast, the other acids listed are strong acids that dissociate almost completely in water, releasing many more hydrogen ions and making the solution much more acidic. They’re not formed simply by dissolving carbon dioxide in water, which is why carbonic acid is the correct choice.