Reaction of a carboxylic acid with carbonate produces which of the following?

• A. A salt, carbon dioxide, and water
• B. A salt and water only
• C. Hydrogen gas and water
• D. Carbon dioxide only

Answer: (A)

Carboxylic acids react with carbonates in a neutralization that also releases carbon dioxide. The acid donates a proton to the carbonate, forming the carboxylate salt and carbonic acid; the carbonic acid then decomposes to CO2 and H2O. So the overall products are the carboxylate salt, carbon dioxide, and water. For example, R-COOH plus NaHCO3 gives R-COONa plus CO2 and H2O (and with Na2CO3 you’d get more salt in the same way). The evolution of CO2 gas is the telltale sign that CO2 is produced, not hydrogen gas, and you do get the salt alongside the gas and water rather than CO2 alone.