Neutralizing acidity with lime

Soils becoming too acidic is a significant problem in agriculture and in home lawns and gardens. It is countered by adding crushed limestone often called agricultural lime or “aglime” to the soil. See:

The most common ingredient of “aglime” is calcium carbonate CaCO3. In the presence of acid (H⁺), CaCO₃ ionizes  to form Ca⁺⁺ and CO3^—.

Two H⁺ join with the CO₃^—  to make H₂O and CO₂ thus neutralizing the soil.

This reaction also goes in the opposite direction, CO₂ combins with water make carbonic acid (CO₂ + H₂O —> 2H⁺ + CO3^—). This is a serious ecological problem as excessive CO2 dissolves in oceans making them more acidic. See: Oceanic acidification/ Please post questions.