Which equation represents the formation of calcium bicarbonate from calcium carbonate and carbonic acid?

• A. Ca2+ + CO3^2- → CaCO3
• B. HCO3- + H+ → H2CO3
• C. Fe + Cu2+ → Fe2+ + Cu
• D. CaCO3 + H2CO3 → Ca(HCO3)2

Answer: (D)

When a carbonate mineral like calcium carbonate meets carbonic acid, it dissolves to form a soluble calcium bicarbonate. The equation CaCO3 + H2CO3 → Ca(HCO3)2 shows calcium carbonate reacting with carbonic acid to yield calcium bicarbonate, with calcium coordinating two bicarbonate ions. This mirrors how carbon dioxide dissolves in water to form H2CO3 and how the carbonate ion combines with that acid to stay in solution as Ca(HCO3)2. The balance checks out: one calcium, two carbons, six oxygens, and two hydrogens appear on both sides, keeping the equation consistent.

Other options don’t describe this dissolution process. One represents formation of solid calcium carbonate from ions, which is the reverse scenario. Another is a simple proton transfer between acids and bases that doesn’t involve calcium. The last is a redox-type reaction between metals, which is irrelevant to carbonate chemistry.