Calcium carbonate
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Calcium carbonate is a chemical compound, with chemical formula CaCO3. It is commonly used medicinally as a calcium supplement or as an antacid. Calcium carbonate is the active ingredient in agricultural lime. It is a common substance found as rock in all parts of the world and is the main component of seashells and the shell of snails.
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Occurrence
Calcium carbonate is found naturally as the following minerals and rocks:
Eggshells are composed of approximately 95% calcium carbonate.
To test whether a mineral or rock contains calcium carbonate, strong acids like hydrochloric acid can be dropped with a dropper onto it. If it does contain the chemical, it will fizz and produce carbon dioxide; otherwise, it probably wouldn't react vigorously. For example, all of the rocks/mineral mentioned above will react with acid.
Preparation
The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. When pure calcium carbonate is required (e.g. for food or pharmaceutical use), it is prepared by passing carbon dioxide into a solution of calcium hydroxide: the calcium carbonate precipitates out, and this grade of product is referred to as a precipitate.
- Ca(OH)2 + CO2 → CaCO3 + H2O
Chemical properties
- See also: Carbonate
Calcium carbonate shares the typical properties of other carbonates. Notably:
- it reacts with strong acids, releasing carbon dioxide.
- CaCO3 + 2HCl → CaCl2 + CO2 + H2O
- it releases carbon dioxide on heating (to above 825 °C in the case of CaCO3), to form calcium oxide.
- CaCO3 → CaO + CO2
Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate.
- CaCO3 + CO2 + H2O → Ca(HCO3)2
This reaction is important in the erosion of carbonate rocks, forming caverns, and leads to hard water in many regions.
Uses
The main use of calcium carbonate is in the construction industry, either as a building material in its own right (e.g. marble) or as an ingredient of cement.
Calcium carbonate is widely used medicinally as an inexpensive calcium supplement, antacid, and/or phosphate binder. It is also used in the pharmaceutical industry as a base material for tablets of other pharmaceuticals.
Calcium carbonate is known as whiting in ceramics/glazing applications, where it is used as a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze.
It is commonly called chalk as it has been a major component of blackboard chalk. Chalk may consist of either calcium carbonate or gypsum, hydrated calcium sulfate CaSO4·2H2O.
Recently, calcium carbonate has begun to replace kaolin in the production of glossy paper.
It is also the substance from which the lens of the mammalian eye is made.
In 1989, Dr. Simmons introduced CaCO3 into the Whetstone Brook in Massachusetts. His hope was that the calcium carbonate would counter the acid in the stream from acid rain and save the trout that had ceased to spawn. Although his experiment was a success, it did increase the amounts of aluminum ions in the area of the brook that was not treated with the limestone. This shows that CaCO3 can be added to neutralize the affects of acid rain in river ecosystems.
As a food additive, it is used in some soy milk products.
External links
Template:Expandcs:Uhličitan vápenatý da:Calciumcarbonat de:Kalziumkarbonat es:Carbonato cálcico fr:Carbonate de calcium it:Carbonato di calcio he:סידן פחמתי ja:炭酸カルシウム nl:Calciumcarbonaat pl:Węglan wapnia sv:Kalciumkarbonat th:แคลเซียมคาร์บอเนต zh:碳酸鈣