Calcium bicarbonate

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Calcium bicarbonate
Calcium bicarbonate
Identifiers
PubChem 10176262
ChemSpider 8351767 YesY
Jmol-3D images Image 1
Properties
Molecular formula Ca(HCO3)2
Molar mass 162.11464 g/mol
Solubility in water 16.1 g/100 mL (0 °C)
16.6 g/100 mL (20°C)
18.4 g/100 mL (100 °C)
Hazards
R-phrases R36
Main hazards Irritant
Flash point Non-Flammable
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Calcium bicarbonate, also called calcium hydrogen carbonate, has a chemical formula Ca(HCO3)2. The term does not refer to a known solid compound; it exists only in aqueous solution containing the calcium (Ca2+), bicarbonate (HCO3), and carbonate (CO32–) ions, together with dissolved carbon dioxide (CO2). The relative concentrations of these carbon-containing species depend on the pH; bicarbonate predominates within the range 6.36-10.25 in fresh water.

All waters in contact with the atmosphere absorb carbon dioxide, and as these waters come into contact with rocks and sediments they acquire metal ions, most commonly calcium and magnesium, so most natural waters that come from streams, lakes, and especially wells, can be regarded as dilute solutions of these bicarbonates. These hard waters tend to form carbonate scale in pipes and boilers and they react with soaps to form an undesirable scum.

Attempts to prepare compounds such as calcium bicarbonate by evaporating its solution to dryness invariably yield the solid carbonate instead: Ca(HCO3)2(aq) → CO2(g) + H2O(l) + CaCO3(s).[1] Very few solid bicarbonates other than those of the alkali metals and ammonium ion are known to exist.

The above reaction is very important to the formation of stalactites, stalagmites, columns, and other speleothems within caves and, for that matter, in the formation of the caves themselves. As water containing carbon dioxide (including extra CO2 acquired from soil organisms) passes through limestone or other calcium carbonate containing minerals, it dissolves part of the calcium carbonate and hence becomes richer in bicarbonate. As the groundwater enters the cave, the excess carbon dioxide is released from the solution of the bicarbonate, causing the much less soluble calcium carbonate to be deposited.

Dissolved carbon dioxide (CO2) in rainwater (H2O) reacts with limestone, calcium carbonate (CaCO3) to form soluble calcium bicarbonate (Ca(HCO3)2). This soluble compound is then washed away with the rainwater. This is form of weathering is called 'Carbonation'.

References[edit]

  1. ^ http://www.newton.dep.anl.gov/askasci/chem99/chem99492.htm