Carbon dioxide
Chemists can get carbon dioxide from cooling air. They call this air distillation. This method is inefficient because a large amount of air must be refrigerated to extract a small amount of CO2. Chemists can also use several different chemical reactions to separate carbon dioxide. Carbon dioxide is made in the reactions between most acids and most metal carbonates. For example, the reaction between hydrochloric acid and calcium carbonate (limestone or chalk) makes carbon dioxide: