What is Calcium oxide

Calcium oxide (CaO), also known as slaked lime or burnt lime, is a chemical compound composed of calcium and oxygen. It is a white, crystalline solid at room temperature and is highly alkaline in nature. Calcium oxide is obtained by heating calcium carbonate (usually in the form of limestone) to high temperatures, causing it to undergo thermal decomposition. This process releases carbon dioxide and leaves calcium oxide as a residue.

What is Calcium oxide

Here are some important properties and uses of calcium oxide:


  • Chemical Formula: CaO
  • Molar Mass: 56.08 g/mol
  • Appearance: White, odorless crystalline solid
  • Melting Point: 2,613°C (4,735°F)
  • Boiling Point: Decomposes at high temperature
  • Solubility: Slightly soluble in water, reacts vigorously to form calcium hydroxide (slaked lime)
  • Reactivity: Highly reactive with water, exothermicly producing calcium hydroxide and releasing heat.
  • Acidity/Alkalinity: Calcium oxide is a strong base and can neutralize acids.


  • Construction: Calcium oxide is used in the construction industry to make mortar and plaster. When mixed with water, it reacts to form calcium hydroxide, which hardens over time through a process called hydration, forming a strong binder for building materials.

  • Desiccant: Because of its strong affinity for water, calcium oxide is used as a desiccant (drying agent) to absorb moisture and reduce humidity. It can be used to dry gases and prevent corrosion.

  • Metallurgy: In metallurgical processes, calcium oxide is used as a flux to remove impurities and non-metallic elements from metal ores during smelting.

  • Soil Amendments: Calcium oxide is sometimes added to soil as a soil amendment to raise the pH of acidic soils, reduce soil acidity, and improve soil structure.

  • Sugar Refining: Calcium oxide is used in sugar refining to process raw beet juice and cane sugar, which helps remove impurities.

  • Waste water treatment: It is used in waste water treatment to neutralize acidic waste water and control pH level.

  • Chemical Reagent: Calcium oxide is used as a reactant in various chemical processes, such as the production of calcium carbonate, which is used in industries such as paper making and plastics.

It is important to note that calcium oxide is highly reactive with water and can cause severe burns if it comes into direct contact with the skin or eyes. When using calcium oxide, proper safety precautions should be taken, including using protective equipment and handling it carefully.