Calcium Oxide Quicklime
Calcium oxide (chemical formula: CaO), also called quicklime or burnt lime, is a widely used chemical compound in our daily lives formed by ionic bonding between one calcium atom and one oxygen atom. The white or grayish-white crystalline solid, calcium oxide can be produced in large quantities by driving off carbon dioxide from calcium carbonate. Calcium oxide powder will absorb water to convert itself into lime water or calcium hydroxide and release heat. The relatively inexpensive alkaline oxide, quicklime is dissolved in water, glycerol, and sugar solution but insoluble in alcohol.
The term lime in calcium oxide is connected with calcium-containing inorganic compounds where carbonates, oxides, and hydroxides of calcium, silicon, magnesium, aluminum, and iron predominate.
Quicklime is the oldest used chemical compound, also called burnt lime or lime. It is commonly obtained by heating limestone or shells at high temperatures. It is a commonly used chemical compound for various industries such as steelmaking, construction, agriculture, paper, fertilizers, and more.
Structure of Calcium Oxide
Calcium oxide is formed by ionic bonding between a calcium ion and an oxygen ion with a 1:1 proportion. Therefore, calcium oxide is an ionic compound formed by electrostatic attraction between calcium ions and oxygen ions.
Calcium oxide is a white crystalline solid that appears as a white or gray-white powder or hard lump. In the solid crystalline structure, all the oxygen ions O−2 ions occupy corners and face centers in the FCC arrangement and Ca+2 ions occupy all the octahedral voids.
Properties
Calcium oxide appears as a white or gray, odorless lumps or granular powder. It is a member of alkaline earth metal oxides where calcium and oxygen are present in a 1:1 ratio. Calcium oxide powdered may react readily and explosively with water to form lime water or calcium hydroxide.
The melting point of CaO is very high. Therefore, it cannot be melted at high temperatures and used for the production of light. It is a basic alkaline earth metal oxide that reacts with acid to form their respective salts. For example, when CaO reacts with sulfuric acid it produces calcium sulfate and water.
| Properties | |
| IUPAC Name | Calcium oxide Quicklime Burnt lime |
| Chemical formula | CaO |
| Molar Mass | 56.0774 g/mol |
| Appearance | White or gray, odorless lumps or granular powder |
| Density | 3.34 g/cm3 |
| Melting Point | 2,613 °C |
| Boiling Point | 2,850 °C |
| Solubility | Reacts with water to form lime water or calcium hydroxide but is insoluble in methanol and ethanol |
| Acidity | Basic oxide with pKa = 12.8 |
| Crystal Structure | Cubic crystal structure |
| CAS Number | 1305-78-8 |
Chemical Properties
Calcium Oxide and Water Reaction
When water is added to calcium oxide or quicklime, it will be converted to calcium hydroxide, lime water, or slaked lime with the liberation of enormous heat energy. This process is called slaking of lime.
CaO (s) + H2O (l) → Ca(OH)2 (l) + Heat
Such chemical reaction is strongly exothermic and takes place vigorously with the formation of streams. Such a reaction of CaO with water is sometimes used as a portable source of thermal energy or heat.
Quicklime is a basic oxide of calcium. Therefore, when quicklime is dissolved in water, it exhibits basic properties and shows a pH value of 12.5.
Calcium Oxide and Carbon Dioxide
Calcium oxide or quicklime reacts with carbon dioxide to form calcium carbonate. The reaction is reversible because produced calcium carbonate decomposes at higher temperatures to form calcium oxide and carbon dioxide.
CaO (s) + CO2 (g) → CaCO3 (s)
Quicklime is a basic oxide of calcium and carbon dioxide is an acidic oxide of carbon. Therefore, they combine to form the salt calcium carbonate.
Other Chemical Reactions
Calcium oxide reacts with carbon to form calcium carbide, an important starting material for the production of acetylene fuel.
2 CaO (s) + 5 C (s) → 2 CaC2 (s) + CO2 (g)
When calcium carbide obtained from CaO reacts with water, it releases acetylene gas.
CaC2 + 2 H2O → C2H2 + Ca(OH)2
Acetylene is an important fuel used widely in welding and in the production of various chemical compounds such as vinyl chloride, neoprene, acrylonitrile, many polymers, etc.
Quicklime reacts with sulfur dioxide to form solid calcium sulfate. Therefore, quicklime is used to reduce sulfur dioxide emissions from power plants and air pollution.
CaO + SO2 → CaSO4
The most commercially important chemical property of quicklime is its ability to form a solution when mixed with calcium carbonate and silicates. When we cooled the solution, an amorphous, clear, and nearly colorless solid, namely glass was obtained. Such types of glasses do not have a distinct melting point and used widely from the oldest time.
Production Process
Calcium oxide can produced from calcium carbonate by calcination. In calcination, calcium carbonate from limestone, coral, sea shells, or chalk is converted to calcium oxide and carbon dioxide by thermal decomposition. This reaction can be carried out by heating the materials above 825 °C.
CaCO3 (s) + Heat → CaO (s) + CO2 (g)
The production of quicklime from limestone is one of the oldest chemical transformations produced by human beings. This chemical transformation is not stable because when cooled, it spontaneously reacts with carbon dioxide from the air and is converted back to calcium carbonate. The transformation of calcium oxide to calcium carbonate at room temperature is very slow.
Many chemical properties of quicklime make it the most valuable chemical compound from the oldest times to recent times. For example, it can be used from the oldest time in the production of mortar due to its ability to react with carbon dioxide to regenerate calcium carbonate. However, the reaction of quicklime with carbon dioxide is very slow at room temperature and it can harden very slowly. Such a process can be speeded up by mixing water and sand. Therefore, the producing mortar hardens more
quickly.
Ca(OH)2 + CO2 → CaCO3 + H2O
Quicklime is used widely in various industrial neutralization reactions. Therefore, the worldwide production of quicklime is very large. China and the United States are the largest producers of this valuable chemical compound.
Uses of Calcium Oxide
A broadly utilized chemical compound, calcium oxide or CaO is used widely in our daily lives and chemical industries for cement production, petroleum, and paper industries, agriculture, fertilizers, etc. Therefore, quicklime is the most widely used chemical compound due to its high availability, low toxicity, and chip price to buy. The most common uses of quicklime are:
- Calcium oxide is used to make building materials such as bricks, plaster, mortar, and stucco.
- Quicklime is widely used for the processing of non-ferrous ores.
- In the steelmaking process, quicklime is added to molten iron to remove impurities present in the iron to form slag. Therefore, it can help to improve the purity of the steel.
- Quicklime is used to make aluminum, magnesium, calcium salts, and glass.
- It is used for cleaning beet sugar and canned sugar juice.
- In the paper industry, quicklime is used in the processing of paper pulp because it is highly alkaline.
- In the medicinal or pharmaceutical industry, CaO is used for the development of insecticides and pesticides.
- Quicklime can also be used in drilling fluids, lubricants, and as a bleaching agent in water treatment.
- In science laboratories, it is used for dehydration, precipitation, etc.
- For the production of various calcium compounds, we used quicklime as a starting material.
- Quicklime is also an important chemical that is used for the production of calcium carbide. When calcium carbide reacts with water, it forms acetylene, an important fuel for welding.
- Calcium oxide is used for the reduction of environmental pollution by reducing sulfur dioxide from power plants and phosphate from sewage.
- Calcium oxide can be used with calcium hydroxide to decrease the acidity of drinking water. It also kills the various microorganisms present in water.
Benefits of Quicklime
No direct beneficial effects of quicklime or calcium oxide powder are found on the human body. It can be consumed after converting safe and readily consumable calcium carbonate supplements. The element calcium present in it is the most abundant mineral in our body.
About 99% of calcium is present in the bones and teeth. A small fraction of calcium is found outside the skeleton tissue to perform various biological activities. The main biochemical functions may include:
- Development of bones and teeth
- Muscle construction
- Blood coagulation
- Nerve transmission
- Maintaining membrane integrity and permeability of a cell in biology
- Activating enzymes
- Act as an intercellular messenger
- Activating for the release of hormones
- Contact inhibition and heart functions
In chemistry laboratories, calcium oxide can be used as a reagent for performing precipitation reactions and dehydration. It is a low-price and highly available alkaline earth metal oxide that is used widely in industrial neutralization reactions.
When quicklime is heated to 2,400 °C, it emits light with an intense glow. Such a type of limelight was used widely in old theatrical productions before electric lighting was invented.
A paste of calcium oxide and phenolphthalein can be used to detect water in the petroleum industry. In the presence of water, it formed a basic calcium hydroxide that changes the colour of the phenolphthalein from colurless to pink. Therefore, water in petroleum tanks can be detected by this paste.
Safety
The toxicity of calcium oxide is very low but if inhaled, it may cause coughing, sneezing, and labored breathing in human beings. Quicklime reacts quickly with water by producing a large amount of heat. Therefore, it can burn our skin and eyes when in contact with it.
Frequently Asked Questions
What is quicklime?
Calcium oxide (CaO) is also called quicklime or burnt lime. It is a white or grayish-white caustic alkaline, crystalline substance where calcium and oxygen are present in a 1:1 ratio. It is the most widely used chemical compound that is obtained by heating limestone and combines with water to form lime water and heat.
Is calcium oxide safe?
No, calcium hydroxide is not safe for human beings because it causes irritation when inhaled or placed in contact with moist skin or eyes. The inhalation of CaO may also cause coughing, sneezing, and labored breathing in human beings.
Where to buy calcium oxide?
The toxicity of calcium oxide or quicklime powder is very low. Therefore, we can buy quicklime powder in any nearby general stores or online stores.
What is the difference between quicklime and lime water?
Quicklime is a basic oxide of calcium with the chemical formula CaO. However, lime water is formed when water is added to quicklime. Therefore, lime water is a hydroxide of calcium with the chemical formula Ca(OH)2.
When water is added to calcium oxide or quicklime, it will be converted to calcium hydroxide or lime water with the liberation of enormous heat energy.
