Calcium oxide


CaO molecular structure

Calcium oxide, also known as quicklime or burnt lime, is a white, caustic, alkaline chemical compound, mostly used in construction. It has chemical formula CaO.



Calcium oxide can be reacted, or slaked, with water, releasing large amounts of heat and producing calcium hydroxide. In open air, it reacts with water vapor and carbon dioxide, slowly converting to calcium carbonate over time. It is used as a component of many cement mixes, and can be reacted with acids to form calcium salts.


Calcium oxide is a fine white powder. It reacts violently with water and skin. It is insoluble in methanol.


Calcium oxide can be bought at the construction or home improvement stores as quicklime or burnt lime in sacks or buckets. The ambiguous term "lime" usually refers to a mixture of calcium and/or magnesium compounds, though sometimes may serve as a label for pure calcium oxide.


Calcium oxide is prepared from the thermal decomposition of calcium carbonate (lime), at temperatures over 825 °C. If the quicklime is not stable and after it cools, it will spontaneously react with CO2 from the air, converting it back to calcium carbonate. It should also be peformed in a dry environment to prevent hydrolysis back into calcium hydroxide.


  • Homemade cement/concrete
  • Drying solvents
  • Desiccator
  • Make calcium salts
  • Make calcium carbonate



Calcium oxide is extremely corrosive to the human tissue as it reacts vigorously with the water from them, releasing heat which causes severe burns. Quicklime is not normally a fire hazard, but sometimes its reaction with water can release sufficient heat to ignite combustible materials. Neutralizing calcium oxide even with a weak acid will release copious amounts of heat. Intentionally mixing calcium oxide with water in a controlled and well-thought out setup can be used to produce the somewhat more stable calcium hydroxide. Gloves, face mask and goggles should be worn when handling the powder, as most the commercial powder is extremely fine and can easily become airborne.


Calcium oxide should be stored in closed or sealed bottles, in a dry place, to prevent it from absorbing water and carbon dioxide from air.


Calcium carbonate should be neutralized before being discarded of. It doesn't pose any hazards to the environment after being neutralized and can be safely dumped in the ground.


Relevant Sciencemadness threadsEdit

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