All carbonates and hydrogen.carbonates react with dilute acids to liberate carbon dioxide gas. The reaction is always accompanied by vigorous bubbling of gas or effervescence. A delivery tube is used to pass the carbon dioxide gas produced into limewater. Carbon dioxide forms a white precipitate with limewater.

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

The nitrates of metals from calcium to copper in the reactivity series of metals decompose on strong heating to their respective metal oxides, oxygen and nitrogen dioxide gas. The pungent brown gas evolved confirms the presence of a nitrate.

CaCO₃ (s)   ----->   CaO (s) + CO₂ (g)