Calcium oxide – Lime

What is Lime?

Calcium oxide is an odor-free crystalline or powdery solid that, in a pure form, is white to off-gray. It typically appears with a yellow-colored or brownish tint to the presence of impurities, specifically iron. Calcium oxide reacts with water to form calcium hydroxide (Ca(OH)2) with the evolution of considerable amounts of heat. The substance is strongly caustic.

Calcium oxide, likewise called quicklime, is an alkaline compound that has actually been in use given that the medieval age. It is believed that quicklime is among the earliest chemicals known to the human race. It can also be called burnt lime or lime.

How it is prepared?

The procedure for making calcium oxide is believed to be one of the very first chain reaction known to human beings, dating back to ancient times. When limestone (calcium carbonate; CaCO3) is heated, CO2 (CO2) is driven off, leaving calcium oxide behind. The reaction was probably discovered very early in human history because limestone is a common, readily available product in the form of chalk and seashells, and the quantity of heat required to produce the reaction can easily be produced in a basic wood fire.

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A more effective technique for performing the reaction is to heat the limestone in a kiln (oven) at temperatures of 500 ° C to 900 ° C(900 ° F to 1,600 ° F), leading to more complete conversion of calcium carbonate to calcium oxide. This approach is still used today for the commercial preparation of calcium oxide.

Structure of CaO Molecules

Calcium oxide molecules include one calcium cation (which holds a charge of +2) and one oxygen anion (which holds a charge of -2). Hence, it can be understood that calcium oxide is an ionic compound including an ionic bond between calcium and oxygen.


Properties of Calcium Oxide
  • Quick lime is an amorphous white strong with a high melting point of 2600°.
  • It is a really stable compound and stands up to high temperatures.
  • In the existence of water, it forms slaked lime. This process is called the slaking of lime.

CaO+ H2O → Ca (OH)2

  • It is an oxide that is basic in nature and forms salts when it comes in contact with an acid.
  • This substance crystallizes in a cubic crystal lattice.
  • The basic molar entropy related to calcium oxide represents 40 joules per mole kelvin.
  • This compound is understood to release an extreme glow when it is heated up to temperature levels above 2400 degrees Celsius.

CaO+ H2SO4 → CaSO4+ H2O

Uses of Lime/ Calcium oxide
(a) Role of Lime in Agriculture

Large amounts of calcium oxide are utilized in agriculture for neutralizing acidic soils.

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It has been discovered that the application of lime to acidic soils increases the quantity of easily soluble phosphorus. Calcium oxide is likewise used in big quantities for making lime-sulfur sprays which have a strong fungicidal action. The hydroxide of calcium is obtained when the oxide of the calcium is enabled to react with water. The procedure is called slaking of lime and it is an exothermic reaction.

(b) Role of Lime in Industries

1.Large amounts of lime are used in the extraction and refining of metals.

  1. Lime is also used in paper, cement, and leather industries.
  2. The capability of lime to react with sand at high temperatures forming calcium silicate (CaSiO3) functions as a crucial basis for glass manufacture.
  3. Lime is used in the ceramic industry for producing different types of sanitary materials.
  4. Regular mortar, also called lime mortar, is prepared by blending freshly prepared slaked lime (one volume) with sand (three or 4 volumes) and water to form a thick paste. This product when placed between the stones and bricks hardens or sets, therefore binding the blocks strongly together. The equations for the chemical reactions which take place when mortar hardens are:

CaO + H2O à Ca (OH)2

Ca (OH)2 + CO2à CaCO3 + H2O

Ca (OH)2 + SiO2à CaSiO3 + H2O

  1. Lime is also utilized in the refining sugar and other food products.
  2. Lime is utilized in the manufacturing of whitening powder, which is utilized for the bleaching of the fabric and paper pulp.
  3. A suspension of the calcium hydroxide is called milk of lime and is used as a white-wash.
  4. When lime is heated with coke at about 2800 ° C in an electrical heater, calcium carbide is produced, which on hydrolysis yields acetylene (C2H2).

CaO + 3C à CaC2 + CO  (Calcium Carbide)

  1. Lime is typically used as a dehydrating agent, for instance, in the preparation of absolute alcohol and the drying of ammonia gas. A mix of sodium hydroxide and calcium hydroxide (soda lime) is typically used to remove both water and carbon dioxide from certain gases.
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