Calcium carbonate
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Calcium carbonate is a chemical compound, with chemical formula CaCO3.
It is commonly used as an antacid, and 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.
Occurance
Calcium carbonate is found naturally as the following minerals and rocks:
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 precipitated.
- 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 in the pharmaceutical industry, either as an antacid or 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 also the main component of blackboard chalk.