Calcium Oxide (CaO), commonly known as raw lime or baked lime, is a widely used chemical compound. Calcium oxide is an alkaline crystal, caustic, white solid at room temperature. The broad term used “lime” connotes inorganic materials containing calcium, which include carbonates, oxides and calcium hydroxides, silicon, magnesium, aluminum, and iron dominating, such as limestone. In contrast, “raw lime” specifically applies to single chemical compounds.
Raw chalk is relatively cheap. Both and chemical derivatives (calcium hydroxide, which is raw lime is anhydride alkaline) which is important commodity chemicals.
Calcium oxide, is also called Raw chalk, Burn lime, Tohor lime. Calcium Oxide characteristics are:
- Molecular formula: CaO
- Molecular weight: 56.0774 gr / mol
- Appearance: White to pale yellow / brown powder
- Odor: Odorless
- Density: 3.34 gr / cm3
- Melting point: 2613 ° C, 2886 K, 4735 ° F
- Boiling Point: 2850 ° C, 3123 K (100 hPa)
- Water solubility: 1.19 g / L (25 ° C); 0.57 g / L (100 ° C); exothermic reaction
- Solubility in acid: Soluble (also in glycerol, sugar solution)
- Solubility in methanol: Insoluble (also in diethyl ether, n-octanol)
- Acidity (pKa): 12.8
- Standard molar entropy So298: 40 J • mol-1 • K-1
- Entalpy of standard formation ΔfHo298: -635 kJ • mol-1
- Flash point: Not burning
Calcium oxide is usually made by thermal decomposition of materials such as limestone, or shell of shells (or other molluskic shells), containing calcium carbonate (CaCO3, calcite minerals) as lime kilns. This is done by heating this material above 825 ° C (1,517 ° F), a process called calcination or lime-burning, to liberate the carbon dioxide (CO2) molecule; leave the lime.
The lime is unstable and, when cooled, will spontaneously react with CO2 from the air until enough time, it will be completely converted back into calcium carbonate unless it is watered with water to be designated as lime plaster.
Annual production of raw chalk worldwide is around 283 million metric tons. China is by far the largest producer in the world, with a total of around 170 million tons per year. The United States is the next largest, with about 20 million tons per year.
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The Uses of Calcium Oxide in Daily Life
Here are the uses of calcium oxide in daily life:
1. Produce Heat
The raw lime generates heat energy by the formation of hydrate, calcium hydroxide, with the following equation:
CaO (s) + H2O (l) = Ca (OH) 2 (aq) (ΔHr = -63.7 kJ / mol CaO)
Like hydrate, a result of exothermic reactions and solids swells. Hydrate can be converted into raw lime by removing water by heating it up until the color of it becomes redness to reverse the hydration reaction. One liter of water that joins about 3.1 kilograms (6.8 lb) of lime provide calcium hydroxide plus 3.54 MJ of energy.
This process can be used to provide a convenient portable heat source, such as for heating food immediately in its own heating premises. (Read Chemicals allowed in organic food)
2. Produce Light
When raw lime is heated to 2400 ° C (4,350 ° F), this lime emits intense light. This form of lighting is known as limelight, and is widely used in theater production before the invention of electric lighting. (Read Chemicals that glow under black light)
3. Ingredient for Cement and as Alkaline
Calcium oxide is a key ingredient for the cement making process. Calcium oxide is also used as an alkaline in biodiesel production.
4.To Detect Water in Petroleum Industry
The water-detecting paste contains a mixture of calcium oxide and phenolphthalein. This paste must be present to make contact with water in a fuel storage tank. CaO reacts with water to form calcium hydroxide. Calcium hydroxide has a high enough pH to convert phenolphthalein into pink – clear purplish, thus indicating the presence of the water.
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5. To Produce Sodium Hydroxide in Paper Industry
Calcium oxide is used to produce sodium hydroxide from sodium carbonate in chemical recovery at Kraft pulp mill. (Read also Inorganic Water Pollutants)
6. As Plaster
There is archaeological evidence that Neolithic B Pre-Pottery (pottery sticks) uses lime-based plaster for flooring and other uses. The ash-lime floor remained in use until the late of nineteenth century. (Read Chemicals in Joint Compound)
7. Chemical or Power Production
Solid spray or calcium oxide pulp can be used to remove sulfur dioxide from the exhaust flow in a process called flue gas desulfurization.
8. Shrimp Culture Industry
In the industry of shrimp or tiger shrimp culture, lime is popularly used as an alkaline substance to anticipate the decline in pH of pond water due to rain. Usually Tohor lime is sown on the edge of the shrimp pond in the rainy season.
9. As Weapon
Historian and philosopher David Hume, in his book on English history, recounts that in the early of the reign of Henry III, the British Navy destroyed the French fleet by blinding enemy fleets with chalk.
Raw chalk is also considered to be a component of the Greek fire. At its contact with water, lime will increase its temperature above 150 ° C and ignite the fuel.
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10. Making Bitan Egg
Tohor Chalk with its basic properties are also used in making bitan eggs. Bait eggs (simple Hanzi: 皮蛋; pinyin: pídàn; pronunciation: / bitan /), black egg, or thousand-year eggs are typical Chinese foods made from chicken eggs or ducks preserved in clay, ash, salt, lime and rice husks for weeks or months, depending on process method.
During preserved, the yolk will turn dark green and become like a cream with the smell of sulfur and ammonia, while the egg white turns brown and slightly transparent.
Eggs change due to the presence of alkaline materials that raise the pH of the eggs to 9 or more. This chemical process destroys some of the complex protein and fat contents in an egg that initially does not taste to taste and smell strong. Sometimes the eggs have shades such as pine branches in the white part.
Cautions of Calcium Oxide
Those all the uses of calcium oxide in our daily life. Things that we should consider are :
Due to the overwhelming reaction of lime with water, lime causes severe irritation when inhaled or in contact with moist skin or eye. Inhaling this substance can cause coughing, sneezing, shortness of breath. It can then develop into burn scar with perforation of the nasal septum, abdominal pain, nausea and vomiting.
Although lime is not considered a fire hazard, however its reaction with water can release enough heat to ignite the flammable material.
Hope this article is helpful to understand the uses of calcium oxide in daily life.