In the characteristic reaction method, if the insoluble solid is carbonate reacting with acid, what is formed?

• A. Metal salt + water + CO2
• B. Metal salt + CO2 only
• C. Metal salt + hydrogen
• D. Water and CO2 only

Answer: (A)

When a carbonate reacts with an acid, the hydrogen ions from the acid neutralize the carbonate, producing carbon dioxide gas and water. Simultaneously, the metal from the carbonate forms a salt with the anion from the acid. For example, CaCO3 reacting with hydrochloric acid gives CaCl2 plus CO2 and H2O. So the overall products are the metal salt, water, and carbon dioxide. The other possibilities miss one of these products or suggest hydrogen gas, which isn’t formed in this reaction.