See also: Carbonate (homonymy)
In Chemistry, carbonate indicates a Ion formed of a Atome of Carbone and three atoms of Oxygène carrying a double negative electric charge (CO32-), as well as a chemical Composé including/understanding this Anion.
StructureIn the Ion CO32-, each carbon atom is in the center of an equilateral triangle whose each top is occupied by an atom of Oxygène. No ion oxygen is common to two triangular groupings carbon-oxygens; those must be regarded as distinct units in the structure of carbonated minerals and they are mainly responsible for the particular properties of this group.
The connection between central carbon and oxygens is less strong than in the Carbon dioxide. In the presence of the hydrogen ion, the radical carbonate becomes unstable and breaks. This instability is at the origin of the tests to the acid which make it possible to recognize carbonates in an organic compound or inorganic. In contact with a solution of Hydrochloric acid HCl, the CO32- ions form CO2 carbon dioxide, whose gaseous emission is observable in the form of effervescence.
When the ion carbonate is combined with the divalent Cation S (Ca2+, Fe2+…), it forms compounds of simple geometrical structure, generally Rhomboédrique or Orthorhombique. The calcium carbonate crystallizes at the same time with the rhomboedric structure of the Calcite and the orthorhombic structure of the Aragonite.
PropertiesThe carbonates are mineral that one finds in abundance on the surface of the Earth. The calcium carbonate is the constituent main thing of the shell S of many organizations. One especially finds it in the Lithosphère in the form of the rocks known as limestones, most abundant among the sedimentary rocks. This considerable carbon stock is fed by the Métabolisme living beings in the form of carbonic gas, which gives in particular, while combining with divalent metals, of the insoluble compounds under the normal conditions of the lithosphere: carbonates. Later dissociations can however intervene, with the favor of which carbon put in reserve is restored with the biosphere and the atmosphere. Thus the carbonates are with cross cycles biochemical and geochemical of carbon, primarily localized in the surface zone of the lithosphere. The presence of carbonates in the rocks of internal origin is, indeed, exceptional and it poses one of the most interesting problems of petrology, that of the “primary” origin of in-depth carbon.
The alkaline carbonates dissociate only at very high temperature, the alkaline-earth carbonates and the lithium carbonate at less high temperature; the temperature to which a given carbonic gas pressure is reached decrease barium carbonate to magnesium carbonate, while passing by strontium then calcium. The water soluble alkaline carbonates are hydrolized.
Carbonate calciumThe Roche S carbonated are sedimentary rocks made up of a great proportion of carbonate; often carbonate of Calcium (CaCO3).
Examples:Calcite (system rhomboedric) which is the most stable form and the Aragonite (orthorhombic system) which is the form which crystallizes naturally in the current oceans. Another variety is the Vatérite, but this form is very unstable under the conditions of pressure and temperature normals.
Various types of carbonates
- Carbonate of Calcium and Magnesium:
- * Dolomite
- Carbonate of Iron:
- * Siderite
- Carbonate of Copper:
- Carbonate of Sodium and Bicarbonate of sodium:
- * Natron
- Carbonate of Calcium, Iron, Manganese and Magnesium:
- * Ankérite
- carbonate of Lead
- * Cerusite: The white lead, of formula (PbCO3) 2 Pb (OH) 2, called white lead or white lead, has been used for more than two thousand years like white pigment. It is also used as coating for ceramics and manufacture of other pigments. Because of the dangers of poisoning by lead, the use of paintings containing this product for interior decoration was mainly prohibited.
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