Calcium Oxide

Calcium Oxide - Properties, Uses and Preparation Calcium Oxide

Compound Name: Calcium oxide.

Other names are: Lime; quicklime; fluxing lime; unslaked lime

Formula: CaO
Elements: Calcium, oxygen
Compound type: Metallic oxide
State: Solid
Molecular weight: 56.08 g/mol
Melting point: 2,572°C (4,661°F)
Boiling point: 28500 C


Calcium oxide is a non-aromatic crystalline or powdery solid that, in a pure form, is white to off-grey colour. It frequently appears with a yellowish or brownish shade because of presence of impurities, particularly iron. The compound is highly caustic. 

Calcium oxide has been known since ancient times. The Roman writer Cato the Elder (234–149 bc) mentioned one method of making the compound in 184 BC. By the early fifteenth century, many of European was using calcium oxide (generally referred to as lime) in the construction of buildings. The Scottish chemist Joseph Black (1728–1799) performed some of the earliest scientific studies of calcium oxide. He found that when the compound is exposed to air, it combines with carbon dioxide to produce calcium carbonate.

Calcium oxide (CaO), is generally known as quicklime or burnt lime, it is a commonly used chemical compound. It is solid at room temperature. The broadly used word lime means calcium containing inorganic materials, in which oxides and hydroxides of calcium, magnesium, aluminium, silicon and iron are present. By contrast, quicklime precisely applies to the single chemical compound calcium oxide. But commercial lime frequently contains impurities. It is prepared by heating calcium carbonate (e.g., limestone) in a distinct lime kiln to about 500°C to 600°C, decompose it into the oxide and carbon dioxide.


The procedure for making calcium oxide is thought to be one of the first chemical reactions known to the human being, dating back to Stone Age times. When limestone (calcium carbonate; CaCO3) was heated, carbon dioxide (CO2) was driven off, leaving calcium oxide behind. The reaction was perhaps discovered early in human history because limestone is a publicly, readily available material in the form of chalk and seashells, and the volume of heat needed to create the reaction can easily be produced in a simple wood fire. A more effective method for carrying out the reaction is to heat the limestone in an oven at temperatures of 600°C to 100°C (1100°F to 1,600°F), resulting in a more complete change of calcium carbonate to calcium oxide. This technique is still used today for the commercial preparation of calcium oxide.

Raw Materials required for preparation:

Magnesium carbonate and Calcium carbonate acquired from deposits of limestone, chalk, dolomite, oyster shells, stalactites, marble, and stalagmites. Vertical or horizontal kilns (oven) are used to burn limestone. The kilns (oven) have steel shells lined with refracting blocks.

Calcium oxide or lime is prepared by the process called calcination. Calcium carbonate or Limestone is heated to a temperature between 1250 ⁰C and 1400 ⁰C in Kilns (oven) and it decomposes to quicklime and carbon dioxide.

A Vertical Lime Kiln or (oven):

Calcium oxide is typically made by the thermal decomposition of materials, such as seashells or limestone, that have calcium carbonate (CaCO3; inorganic calcite) in a lime kiln. This is achieved by heating the material to above 835 °C (1,517 °F), a process is known as calcination or lime-burning, to release a molecule of carbon dioxide (CO2), leaving quicklime.

CaCO3(s) → CaO(s) + CO2(g)

The quicklime is not steady or stable and, when cooled, will suddenly react with CO2 from the air until, all the carbon dioxide is used, and it will be completely converted back to calcium carbonate if not slaked with water to set as lime plaster or lime mortar.

Yearly worldwide production of quicklime is around 285 million tons. China is by far the world's largest producer, with a sum of around 190 million tons per year. The United States is the second largest, with around 20 million tons per year.

Roughly 1.8 tons of limestone is necessary per 1.0 t of quicklime. Quicklime has a high attraction for water and is a more effective desiccant than silica gel.

Chemical Properties:

  • • Quick lime forms slaked lime or lime water on hydration. When water is added to lime it becomes hot and cracks to form a white powder. This is known slaking of lime.

  • • Calcium oxide is a basic oxide which can react with acids and give calcium salts.

  • • It forms silicates and phosphates with acidic oxides like silicon dioxide and phosphorus pentoxide. This property will make lime useful as a flux in metallurgy which removes impurities.

  • Properties of Quick Lime:

  • • Lime is a white shapeless or amorphous solid.

  • • It has a high melting point of 2572oC.

  • • It is extremely stable and even fusion cannot decompose it.

  • Solubility:

    In water: Reacts with water to produce calcium hydroxide.
    In Acids: It also soluble in acids.
    In Alcohols: it is insoluble in alcohol
    In Organic: soluble with most of organic solvents.

    Uses of Lime:

  • • Lime is used for medicinal purposes, plant, insecticides and animal food.

  • • It is also used as a laboratory reagent for gas absorption, dehydration, and precipitation etc.

  • • It is used as a reagent in the production of paper, cement, and high-grade steel.

  • • It finds use in detailing hides.

  • • It can be used as water softening and in the recovery of ammonia

  • • It finds vast use in the production of soap, varnish, refractories, rubber, and lime bricks.

  • • It also finds use in the making of calcium carbide, nitrate, basic calcium, and calcium bisulphite.

  • • Improves soil quality.

  • • It is used in water treatment plants, to control the acidity of the water being treated and to treat impurities present in the water;

  • • Act as a filler to strengthen paper products;

  • • It can be used as a refractory, a heat-resistant material used to line the insides of furnaces;

  • • In the manufacture of other chemical materials;

  • • As a preservative for poultry feed;

  • • Used in insecticides and fungicides;

  • • It is also used in the removal of hair from hides before tanning.

  • • It is also used as a food additive to maintain proper acidity and give bulk to a food product.

  • Interesting Facts about Calcium oxide:

  • • Calcium oxide is frequently used to "lime" lake waters that have been acidified by acid rain it reacts with them and neutralizes acids in the lake. It also formed when nitric and sulfuric acid in acid rain are carried to earth by rain, sleet, snow, and other methods of precipitation.

  • • When calcium oxide is heated near its melting point, it gives off a bright white light. In the years before electricity was discovered for lighting, particularly during the second half of the nineteenth century it was used as lime light source, heated lime was used to create the bright lights required to illuminate stage productions.

  • • Because it was thought to increase the speed in decomposition of soft tissue, quicklime has historically been used in the funeral of diseased animals and humans. For instance, bodies of plague victims in London in 1666 were instructed to be buried in quicklime.

  • Health Risk:

    Contact to calcium oxide can cause injury to the skin, nose, eyes, and respiratory system. People who use the product in their line of work or at home for (garden purposes) for example, people who are working must be extreme caution not to breathing in, swallowing, or otherwise coming into contact with the chemical. If such contact occurs, it should be washed off completely with water and ask for medical assistance.