Which gas is evolved when a metal carbonate reacts with sulfuric acid?

• A. Carbon dioxide.
• B. Hydrogen.
• C. Oxygen.
• D. Nitrogen.

Answer: (A)

When a carbonate reacts with an acid, the carbonate neutralizes the acid and releases carbon dioxide gas, leaving behind a salt and water. In a metal carbonate reacting with sulfuric acid, the carbonate ions react with the hydrogen ions from the acid to form carbon dioxide, while the metal forms a sulfate. The overall result is metal sulfate plus carbon dioxide and water. This is why the gas evolved is carbon dioxide, which can be tested by passing it through limewater to see a milky precipitation. The other gases listed would come from different reactions (for example, hydrogen would come from a metal reacting with an acid to release H2, not from a carbonate reacting with sulfuric acid).