Calcium Hydroxide vs. Calcium Oxide

What's the Difference?

Calcium hydroxide and calcium oxide are both compounds that contain calcium, but they have different chemical properties and uses. Calcium hydroxide, also known as slaked lime, is a white powder that is slightly soluble in water. It is commonly used in agriculture to adjust soil pH and in construction as a component of mortar and plaster. On the other hand, calcium oxide, also known as quicklime, is a white crystalline solid that is highly reactive with water. It is primarily used in industries such as steel production, paper manufacturing, and water treatment. Calcium oxide is also used in the production of cement and as a desiccant due to its ability to absorb moisture.


AttributeCalcium HydroxideCalcium Oxide
Chemical FormulaCa(OH)2CaO
Common NameLimeQuicklime
AppearanceWhite powder or colorless crystalsWhite crystalline solid
Solubility in WaterPartially solubleInsoluble
pH Level12-13 (basic)12-13 (basic)
UsesUsed in construction, agriculture, and water treatmentUsed in the production of cement, as a drying agent, and in the manufacturing of glass
Reaction with WaterForms a strong alkaline solutionForms calcium hydroxide (slaked lime)

Further Detail


Calcium hydroxide (Ca(OH)2) and calcium oxide (CaO) are both chemical compounds that contain calcium. They are commonly used in various industries and have distinct attributes that make them suitable for different applications. In this article, we will explore the characteristics, properties, and uses of calcium hydroxide and calcium oxide, highlighting their similarities and differences.

Chemical Composition

Calcium hydroxide, also known as slaked lime or hydrated lime, is composed of one calcium atom, two oxygen atoms, and two hydrogen atoms. Its chemical formula is Ca(OH)2. On the other hand, calcium oxide, also called quicklime or burnt lime, consists of one calcium atom and one oxygen atom, with the chemical formula CaO.

Solubility and Reactivity

One of the key differences between calcium hydroxide and calcium oxide lies in their solubility and reactivity. Calcium hydroxide is highly soluble in water, forming a saturated solution known as lime water. This solution has a pH of around 12 and is commonly used in various applications, including water treatment, construction, and food processing.

On the other hand, calcium oxide is sparingly soluble in water, meaning it dissolves to a lesser extent compared to calcium hydroxide. When calcium oxide reacts with water, it undergoes a highly exothermic reaction, producing calcium hydroxide. This reaction is often used in the process of slaking lime, where calcium oxide is mixed with water to produce calcium hydroxide for various applications.

Physical Properties

Calcium hydroxide appears as a white, odorless powder or crystalline solid. It has a low melting point of approximately 580°C (1076°F) and a relatively high boiling point of around 2850°C (5162°F). The compound has a density of 2.21 g/cm³ and is slightly soluble in alcohol.

Calcium oxide, on the other hand, is a white, caustic, crystalline solid with a high melting point of approximately 2572°C (4662°F). It has a density of 3.34 g/cm³ and is insoluble in alcohol. Calcium oxide is known for its strong alkaline properties and can cause severe burns when it comes into contact with skin or eyes.


Both calcium hydroxide and calcium oxide have a wide range of applications in various industries due to their unique properties.

Calcium Hydroxide Uses

  • Water Treatment: Calcium hydroxide is commonly used in water treatment processes to adjust the pH levels and remove impurities.
  • Construction: It is used in the construction industry for mortar and plaster applications, providing strength and durability to structures.
  • Food Processing: Calcium hydroxide is used in food processing, particularly in the production of corn tortillas, where it helps in the removal of the outer skin of corn kernels.
  • Waste Treatment: It is utilized in waste treatment facilities to neutralize acidic waste and control odors.
  • Medical and Dental Applications: Calcium hydroxide is used in dental materials, such as dental liners and pulp capping agents, due to its antimicrobial and alkaline properties.

Calcium Oxide Uses

  • Steel Production: Calcium oxide is a crucial component in the steelmaking process, where it is used to remove impurities and control the slag composition.
  • Soil Amendment: It is used as a soil amendment to increase the pH levels in acidic soils, promoting better plant growth.
  • Chemical Industry: Calcium oxide is utilized in various chemical reactions, such as the production of calcium carbide, calcium hypochlorite, and calcium stearate.
  • Desiccant: Due to its strong affinity for water, calcium oxide is used as a desiccant or drying agent in certain applications.
  • Construction: It is used in the construction industry for stabilization and drying of soils, as well as in the production of cement and concrete.

Environmental Impact

Both calcium hydroxide and calcium oxide can have environmental implications, particularly when mishandled or disposed of improperly.

Calcium hydroxide, when released into water bodies in excessive amounts, can increase the pH levels, leading to potential harm to aquatic life. However, it is worth noting that calcium hydroxide is generally considered safe when used in appropriate concentrations and following proper guidelines.

Calcium oxide, on the other hand, can react with water vapor in the atmosphere to form calcium hydroxide, a process known as slaking. This reaction releases heat and can contribute to air pollution. Additionally, the caustic nature of calcium oxide can cause harm to living organisms if not handled with care.


In conclusion, calcium hydroxide and calcium oxide are two important compounds that contain calcium. While calcium hydroxide is highly soluble in water and has various applications in water treatment, construction, and food processing, calcium oxide is sparingly soluble and finds uses in steel production, soil amendment, and chemical reactions. Understanding the distinct attributes and properties of these compounds is crucial for their safe and effective utilization in various industries.

Comparisons may contain inaccurate information about people, places, or facts. Please report any issues.