Carbonate ion (CO₃²⁻)
- Charge
- −2
- Atoms
- C, O × 3
- Atoms in total
- 4
- Mass of the ion
- 60.008 g/mol
Carbonate is one carbon atom bonded to three oxygen atoms, with a 2− charge shared across the three oxygens. It is what is left when carbonic acid, H₂CO₃, loses both of its hydrogen ions. Carbonates make up chalk, limestone, marble and seashells, and they are in washing soda and many antacids.
- Adding one H⁺ to carbonate gives hydrogen carbonate, HCO₃⁻, the bicarbonate in baking soda.
- Carbonates fizz when an acid is added because they release carbon dioxide gas, a quick test used in geology and school labs.
- Calcium carbonate, CaCO₃, is the mineral in limestone, chalk, marble and eggshells.