Calcium+carbonate

Calcium carbonate has the chemical formula of CaCO 3. It is found in chalk, limestone, and marble, and accounts for 4% of earth's crust. When it comes in contact with any acid, it produces carbon dioxide. Other than being used on blackboards in classrooms, it can be used in mining and as a dietary supplement.

Carbonate is found frequently in geologic settings and constitute an enormous carbon reservoir.

Calcium carbonate can reacts with strong acids, releasing carbon dioxide. It can be divided into two parts on heating (above 840 °C), forming calcium oxide and releasing carbon dioxide.

Calcite commonly occurs as sediments in marine settings. Calcite is typically found around the warm tropic environments. Calcite precipitates in warmer shallow environments more than it does under colder environments because warmer environments do not favor the dissolution of CO2. This is analogous to CO2 being dissolved in soda. When you take the cap off of a soda bottle, the CO2 rushes out. As the soda warms up, carbon dioxide is released. This same principle can be applied to calcite in the ocean. Cold-water carbonates do exist at higher latitudes but have a very slow growth rate.

Calcium carbonate may cause side effects. upset stomach, vomiting, stomach pain, belching, constipation, dry mouth, increased urination, loss of appetite, metallic taste


 * Chemical properties **

Calcium carbonate shares the typical properties of other carbonates. Notably:


 * it reacts with strong acids, releasing carbon dioxide:

CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
 * it releases carbon dioxide on heating (to above 840 °C in the case of CaCO3), to form calcium oxide, commonly called quicklime , with reaction enthalpy 178 kJ / mole:

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.


 * Preparation **

The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (e.g. for food or pharmaceutical use), can be produced from a pure quarried source (usually marble).

Alternatively, calcium carbonate is prepared by calcining crude calcium oxide. Water is added to give calcium hydroxide, and carbon dioxide is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate (PCC):

CaCO3 → CaO + CO2CaO + H2O → Ca(OH)2Ca(OH)2 + CO2 → CaCO3 + H2O