International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

In the reaction between an acid and metal carbonate, what byproducts are formed?

1. Salt + hydrogen + water

2. Salt + carbon dioxide + water

3. Salt + hydrogen + oxygen

4. Salt + water + sulfur dioxide

The correct answer is: Salt + carbon dioxide + water

The reaction between an acid and a metal carbonate is a well-established chemical process where the acid reacts with the carbonate to produce specific byproducts. In this reaction, the carbonate (which contains the carbonate ion, CO₃²⁻) reacts with the acid, resulting in the formation of a salt (which is the metal salt derived from the acid), carbon dioxide (CO₂), and water (H₂O). When the acid donates its hydrogen ions (H⁺) to the carbonate ions, the carbonate decomposes and releases carbon dioxide gas as a byproduct. The remaining part of the carbonate combines with the hydrogen ions from the acid, forming the salt. The water is also produced due to the combination of hydrogen ions and hydroxide ions, which may be present if the acid is aqueous. Thus, the correct answer highlights the typical products of this reaction: the salt formed from the metal cation and the anion of the acid, carbon dioxide as a gas that can be seen bubbling out of the solution, and water as part of the reaction mixture. This understanding is important in distinguishing the outcomes of acid-base reactions involving carbonates.