Metal carbonates such as calcium carbonate (chalk) react with acids to produce the gas carbon dioxide. This can be seen in the equation:

Metal carbonate + Acid Salt + Water + Carbon dioxide

The carbon dioxide produced can be tested for in the lab using limewater, which reacts with the carbon dioxide gas. When the limewater reacts with carbon dioxide gas it turns from colourless to milky white in colour.

NB: bear in mind that the limewater isn't actually blue! It's colourless.

The salt produced depends on the acid that's used to produce it. The table below shows the type of salts that are produced from these acids:

The name of the salts produced is better illustrated in an equation:

Hydrochloric Acid

Magnesium carbonate + Hydrochloric acid Magnesium chloride + Water + Carbon dioxide

MgCO₃+ 2HClMgCl₂ + H₂O + CO₂

Sulfuric Acid

Calcium carbonate + Sulfuric acid Calcium sulfate + Water + Carbon dioxide

CaCO₃+ H₂SO₄CaSO4 + H₂O + CO₂

Nitric Acid

Sodium carbonate + Sulfuric acid Sodium nitrate + Water + Carbon dioxide

Na₂CO₃+ 2HNO32NaNO3 + H₂O + CO₂