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 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 reactions 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.

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 the 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 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 of 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.

MCQs with Answers

  1. What is the common name for calcium oxide?
    • a) Calcium Carbonate
    • b) Quicklime
    • c) Calcium Hydroxide
    • d) Calcium Sulfate
    • Answer: b) Quicklime
  2. How is calcium oxide typically prepared?
    • a) Precipitation
    • b) Oxidation
    • c) Heating limestone
    • d) Electrolysis
    • Answer: c) Heating limestone
  3. What is the structure of calcium oxide molecules?
    • a) Covalent bond
    • b) Ionic bond
    • c) Metallic bond
    • d) Polar bond
    • Answer: b) Ionic bond
  4. What is the temperature range for heating limestone in the industrial preparation of calcium oxide?
    • a) 100°C – 200°C
    • b) 300°C – 400°C
    • c) 500°C – 900°C
    • d) 1000°C – 1200°C
    • Answer: c) 500°C – 900°C
  5. Which of the following is a property of calcium oxide?
    • a) Low melting point
    • b) Acidic nature
    • c) Instability at high temperatures
    • d) Formation of slaked lime in the presence of water
    • Answer: d) Formation of slaked lime in the presence of water
  6. What is the role of calcium oxide in agriculture?
    • a) Neutralizing acidic soils
    • b) Enhancing soil acidity
    • c) Promoting fungal growth
    • d) Improving water retention in soil
    • Answer: a) Neutralizing acidic soils
  7. In the slaking of lime, what is produced when calcium oxide reacts with water?
    • a) Calcium Hydroxide
    • b) Calcium Carbonate
    • c) Calcium Sulfate
    • d) Calcium Chloride
    • Answer: a) Calcium Hydroxide
  8. Which industry uses lime in the extraction and refining of metals?
    • a) Pharmaceutical
    • b) Textile
    • c) Metallurgical
    • d) Petroleum
    • Answer: c) Metallurgical
  9. What is the chemical equation for the formation of calcium silicate (CaSiO3) in the glass manufacturing process?
    • a) CaO + H2O → Ca(OH)2
    • b) Ca(OH)2 + CO2 → CaCO3 + H2O
    • c) Ca(OH)2 + SiO2 → CaSiO3 + H2O
    • d) CaO + 3C → CaC2 + CO
    • Answer: c) Ca(OH)2 + SiO2 → CaSiO3 + H2O
  10. What is lime used for in the ceramic industry?
  • a) Textile bleaching
  • b) Glass manufacturing
  • c) Sanitary material production
  • d) Dehydrating agent
  • Answer: c) Sanitary material production
  1. What is the common name for the traditional mortar prepared with lime and sand?
  • a) Cement
  • b) Plaster
  • c) Concrete
  • d) Lime mortar
  • Answer: d) Lime mortar
  1. What is the primary role of lime in sugar refining?
  • a) pH adjustment
  • b) Dehydration
  • c) Bleaching
  • d) Metal extraction
  • Answer: c) Bleaching
  1. What is the byproduct of heating lime with coke at about 2800°C?
  • a) Calcium Carbonate
  • b) Calcium Carbide
  • c) Calcium Hydroxide
  • d) Calcium Sulfate
  • Answer: b) Calcium Carbide
  1. What is the suspension of calcium hydroxide called and its common use?
  • a) Milk of Magnesia – Medicinal use
  • b) Milk of Lime – Whitewash
  • c) Milk of Sulphur – Fertilizer
  • d) Milk of Potash – Soap production
  • Answer: b) Milk of Lime – Whitewash
  1. What is the role of lime in the drying of ammonia gas?
  • a) Absorbing water
  • b) Absorbing carbon dioxide
  • c) Generating heat
  • d) Promoting gas combustion
  • Answer: a) Absorbing water
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FAQs (Frequently Asked Questions) on Calcium Oxide – Lime

  1. What is lime?
    • Lime, also known as calcium oxide or quicklime, is an odor-free crystalline or powdery solid with a white to off-gray color.
  2. How is calcium oxide prepared?
    • Calcium oxide is prepared by heating limestone (calcium carbonate; CaCO3) to drive off carbon dioxide (CO2), leaving behind calcium oxide.
  3. What is the structure of calcium oxide molecules?
    • Calcium oxide molecules consist of one calcium cation (+2 charge) and one oxygen anion (-2 charge), forming an ionic compound with an ionic bond between calcium and oxygen.
  4. What are the properties of calcium oxide?
    • Quick lime is an amorphous white solid with a high melting point, stable at high temperatures, and reacts with water to form slaked lime (Ca(OH)2). It is basic in nature and crystallizes in a cubic lattice.
  5. What are the uses of lime in agriculture?
    • Lime is used in agriculture to neutralize acidic soils. It increases the solubility of phosphorus and is used in lime-sulfur sprays with fungicidal properties.
  6. How does lime play a role in industries?
    • Lime is used in the extraction and refining of metals, paper, cement, leather, glass manufacture, ceramic production, sugar refining, whitening powder manufacturing, and as a dehydrating agent.
  7. What is the slaking of lime?
    • The slaking of lime is an exothermic reaction where calcium oxide reacts with water to form calcium hydroxide (slaked lime): CaO + H2O → Ca(OH)2.
  8. How is lime used in mortar preparation?
    • Lime mortar, used in construction, is prepared by mixing freshly prepared slaked lime with sand and water. Chemical reactions occur, leading to hardening and binding of blocks.
  9. What is milk of lime, and what is its use?
    • Milk of lime is a suspension of calcium hydroxide. It is used as a white-wash and in various applications such as sanitation and pH adjustment.
  10. What is the industrial significance of calcium oxide?
    • Calcium oxide is crucial in industries for metal extraction, glass manufacturing, ceramic production, and as a dehydrating agent in various processes. It plays a vital role in several chemical and industrial applications.
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Summary: Calcium Oxide – Lime Tutorial

In this comprehensive tutorial on Calcium Oxide, commonly known as Lime, we explored various aspects of its nature, preparation, molecular structure, properties, and diverse applications. Here’s a condensed summary:

1. Introduction to Lime:

  • Calcium oxide, or Lime, is a crystalline or powdery solid with diverse applications. It reacts strongly with water to form calcium hydroxide.

2. Preparation:

  • Lime is primarily prepared by heating limestone (CaCO3), driving off carbon dioxide (CO2), and leaving behind calcium oxide. This process has historical significance and is still employed industrially.

3. Molecular Structure:

  • The molecules of calcium oxide consist of one calcium cation (+2 charge) and one oxygen anion (-2 charge), creating an ionic compound with an ionic bond between calcium and oxygen.

4. Properties:

  • Quick lime is an amorphous white solid with a high melting point, stable at high temperatures, and reacts with water to form slaked lime. It exhibits basic properties, forms salts with acids, and releases intense heat when heated.

5. Uses:

  • Agricultural Role: Used in agriculture to neutralize acidic soils, enhance phosphorus solubility, and as a fungicidal agent in lime-sulfur sprays.
  • Industrial Applications: Essential in metal extraction, paper, cement, leather, glass, ceramics, and sugar refining. Also used in whitening powder production, as a dehydrating agent, and for gas purification.

6. Concluding Thoughts:

  • Lime, with its rich history and versatile properties, plays a pivotal role in various industries and applications, contributing significantly to agriculture, construction, and chemical processes.

This tutorial provides a comprehensive understanding of Calcium Oxide, shedding light on its significance and wide-ranging applications in our daily lives and industrial processes.