chemistry, a carbonate is a salt or esterof carbonic acid.
To test for the presence of the carbonate anion in a salt, the addition of dilute mineral acid (e.g.
hydrochloric acid) will yield carbon dioxide gas.
salts are industrially and mineralogically ubiquitous. The term "carbonate" is also commonly used to refer to one of these salts or carbonate minerals. Most common is calcite, or calcium carbonate, CaCO3, the chief constituent of limestone. The process of removing carbon dioxide from these salts by heating is called calcination.
The term is also used as a verb, to describe the process of raising carbonate and
bicarbonateconcentrations in soda, see also carbonated water, either by the introduction under pressure of carbon dioxidegas into the bottle, or by dissolving carbonate or bicarbonate salts into the water.
tructure and bonding
The carbonate ion is a polyatomic
anionwith the empirical formulaCO32− and a molecular mass of 60.01 daltons; it consists of one central carbon atomsurrounded by three identical oxygen atoms in a trigonal planararrangement, and has "D"3h molecular symmetry. The carbonate ion carries a negative two formal chargeand is the conjugate base of the hydrogen carbonate ion, HCO3−, which is the conjugate base of H2CO3, carbonic acid.
The structure and bonding of the carbonate ion cannot be properly represented by its
Lewis structure, which depicts CO32− with two long single bonds and one short double bond:
Resonance structures can be used to depict the carbonate ion:
In reality, CO32− has three equally long C-O bonds:
A carbonate salt forms when a positively charged ion attaches to the negatively charged oxygen atoms of the ion, forming an ionic compound:
:2M+ + CO32− → M2CO3
:M2+ + CO32− → MCO3
:2M3+ + 3CO32− → M2(CO3)3
Most carbonate salts are insoluble in
waterat standard temperature and pressure, with solubility constants of less than 1×10−8. Exceptions include sodium, potassium and ammonium carbonates.
aqueous solution, carbonate, bicarbonate, carbon dioxide, and carbonic acid exist together in a dynamic equilibrium. In strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the bicarbonateion is prevalent. In more acid conditions, aqueous carbon dioxide, CO2(aq), is the main form, which, with water, H2O, is in equilibrium with carbonic acid - the equilibrium lies strongly towards carbon dioxide. Thus sodium carbonateis basic, sodium bicarbonateis weakly basic, while carbon dioxide itself is a weak acid. Carbonated wateris formed by dissolving CO2 in water under pressure. When the partial pressure of CO2 is reduced, for example when a can of soda is opened, the equilibrium for each of the forms of carbonate (carbonate, bicarbonate, carbon dioxide, and carbonic acid) shifts until the concentration of CO2 in the solution is equal to the solubility of CO2 at that temperature and pressure. In living systems an enzyme, carbonic anhydrase, speeds the interconversion of CO2 and carbonic acid.
The carbonate ion (CO32−) is a moderately strong base. It is a conjugate base of the weakly acidic
bicarbonate( IUPACname hydrogen carbonate HCO3−), itself a moderately strong conjugate base of the still weakly acidic carbonic acid. As such in aqueous solution, the carbonate ion seeks to reclaim hydrogen atoms.
organic chemistrya carbonate can also refer to a functional groupwithin a larger molecule that contains a carbon atom bound to three oxygen atoms, one which is double bonded. These compounds are also known as organocarbonates or carbonate esters, and have the general formula ROCOOR′, or RR′CO3. Important organocarbonates include dimethyl carbonate, the cyclic compounds ethylene carbonateand propylene carbonate, and the toxic triphosgene.
It works as a buffer in the blood as follows:when pH is too low, the concentration of hydrogen ions is too high, so you exhale CO2. This will cause the equation to shift left, essentially decreasing the concentration of H+ ions, causing a more basic pH.
When pH is too high, the concentration of hydrogen ions in the blood is too low, so the kidneys excrete bicarbonate (HCO3−). This causes the equation to shift right, essentially increasing the concentration of hydrogen ions, causing a more acidic pH.
* Carbonate overview:
It is generally thought that the presence of carbonates in rock is unequivocal evidence for the presence of liquid water. Recent observations of the
Planetary nebula NGC 6302shows evidence for carbonates in space [Kemper, F., Molster, F.J., Jager, C. and Waters, L.B.F.M. (2002) The mineral composition and spatial distribution of the dust ejecta of NGC 6302. "Astronomy & Astrophysics" 394, 679-690.] , where aqueous alteration similar to that on Earth is unlikely. Other minerals have been proposed which would fit the observations.
Significant carbonate deposits have not been found on Mars via remote sensing or in situ missions, even though Martian meteorites contain small amounts and groundwater may have existed at both Gusev [Squyres et al., (2007) [http://dx.doi.org/10.1126/science.1139045 doi 10.1126/science.1139045] ] and Meridiani Planum [Squyres et al., (2006) [http://dx.doi.org/10.1029/2006JE002771 doi 10.1029/2006JE002771] ] .
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