8.3.3 Carbonates

Carbonates, which are compounds containing the carbonate ion (CO₃^2-), undergo a chemical reaction with dilute acids. This reaction results in the formation of carbon dioxide gas (CO₂), along with the corresponding salt and water. This reaction is commonly used as a test for the presence of carbonates.

The general equation for the reaction between a carbonate and a dilute acid is as follows:

Carbonate + Dilute Acid → Salt + Water + Carbon Dioxide

For example, when hydrochloric acid (HCl) reacts with calcium carbonate (CaCO₃), the following reaction occurs:

CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g)

The production of carbon dioxide gas during this reaction can be observed and confirmed using limewater (aqueous calcium hydroxide). Limewater turns cloudy or milky when carbon dioxide is bubbled through it or passed into it. This is due to the formation of a white precipitate of calcium carbonate, which indicates the presence of carbon dioxide:

CO₂ (g) + Ca(OH)₂ (aq) → CaCO₃ (s) + H₂O (l)

Not all carbonates react with dilute acids. Some carbonates are insoluble or react very slowly. Furthermore, the reactivity of carbonates can vary depending on the specific metal cation in the carbonate compound.