CaOH

Calcium hydroxide, commonly written Ca(OH)2, is a white, caustic, alkaline solid used widely in industry and agriculture. The shorthand CaOH is sometimes encountered, but the conventional chemical formula is Ca(OH)2.

Production and natural occurrence

Calcium hydroxide is produced by hydrating calcium oxide (quicklime): CaO + H2O → Ca(OH)2. This exothermic reaction yields a colorless solid that readily reacts with acids. In nature, the mineral portlandite corresponds to Ca(OH)2.

Properties

Calcium hydroxide is sparingly soluble in water. At 20–25°C its solubility is about 1.7 g per liter, and the saturated solution (limewater) is highly alkaline with a pH around 12.4–12.6. It reacts with acids to form calcium salts and water. Exposure to atmospheric carbon dioxide slowly converts Ca(OH)2 to calcium carbonate.

Uses

In agriculture, Ca(OH)2 is used to neutralize acidic soils and supply calcium for plant growth. In construction, it is used in lime mortars, plasters, and whitewash. In water and wastewater treatment, it adjusts pH and acts as a coagulant aid. It is also used in the food industry (notably in the nixtamalization process of maize) and in paper production, among other applications.

Safety and handling

Calcium hydroxide is caustic and can cause irritation or chemical burns upon contact with skin or eyes. It should be handled with appropriate protective equipment, and dust should be avoided. It reacts exothermically with acids and slowly carbonates to calcium carbonate when exposed to air.

Storage

Store in a dry, tightly closed container to prevent moisture uptake and carbonation.