Last updated
IUPAC name
Systematic IUPAC name
Trioxidocarbonate [1] :127
3D model (JSmol)
PubChem CID
Molar mass 60.008 g·mol−1
Conjugate acid Bicarbonate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

In chemistry, a carbonate is a salt of carbonic acid (H2CO3), [2] characterized by the presence of the carbonate ion, a polyatomic ion with the formula of CO2−
. The name may also refer to a carbonate ester, an organic compound containing the carbonate group C(=O)(O–)2.

Salt (chemistry) ionic compound

In chemistry, a salt is an ionic compound that can be formed by the neutralization reaction of an acid and a base. Salts are composed of related numbers of cations and anions so that the product is electrically neutral. These component ions can be inorganic, such as chloride (Cl), or organic, such as acetate ; and can be monatomic, such as fluoride (F), or polyatomic, such as sulfate.

Carbonic acid is a chemical compound with the chemical formula H2CO3 (equivalently OC(OH)2). It is also a name sometimes given to solutions of carbon dioxide in water (carbonated water), because such solutions contain small amounts of H2CO3. In physiology, carbonic acid is described as volatile acid or respiratory acid, because it is the only acid excreted as a gas by the lungs. It plays an important role in the bicarbonate buffer system to maintain acid–base homeostasis.

Polyatomic ion as a molecular ion, is a charged chemical species (ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered to be acting as a single unit

A polyatomic ion, also known as a molecular ion, is a charged chemical species (ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered to be acting as a single unit. The prefix poly- means "many," in Greek, but even ions of two atoms are commonly referred to as polyatomic. In older literature, a polyatomic ion is also referred to as a radical, and less commonly, as a radical group. In contemporary usage, the term radical refers to free radicals that are species with an unpaired electron.


The term is also used as a verb, to describe carbonation: the process of raising the concentrations of carbonate and bicarbonate ions in water to produce carbonated water and other carbonated beverages either by the addition of carbon dioxide gas under pressure, or by dissolving carbonate or bicarbonate salts into the water.

Carbonation refers to reactions of carbon dioxide to give carbonates, bicarbonates, and carbonic acid. In chemistry, the term is sometimes used in place of carboxylation, which refers to the formation of carboxylic acids.

Bicarbonate anion

In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula HCO

Carbonated water water containing dissolved carbon dioxide gas

Carbonated water or soda water is water containing dissolved carbon dioxide gas, either artificially injected under pressure or occurring due to natural geological processes. Carbonation causes small bubbles to form, giving the water an effervescent quality. Common forms include sparkling natural mineral water, club soda, and commercially produced sparkling water.

In geology and mineralogy, the term "carbonate" can refer both to carbonate minerals and carbonate rock (which is made of chiefly carbonate minerals), and both are dominated by the carbonate ion, CO2−
. Carbonate minerals are extremely varied and ubiquitous in chemically precipitated sedimentary rock. The most common are calcite or calcium carbonate, CaCO3, the chief constituent of limestone (as well as the main component of mollusc shells and coral skeletons); dolomite, a calcium-magnesium carbonate CaMg(CO3)2; and siderite, or iron(II) carbonate, FeCO3, an important iron ore. Sodium carbonate ("soda" or "natron") and potassium carbonate ("potash") have been used since antiquity for cleaning and preservation, as well as for the manufacture of glass. Carbonates are widely used in industry, e.g. in iron smelting, as a raw material for Portland cement and lime manufacture, in the composition of ceramic glazes, and more.

Geology The study of the composition, structure, physical properties, and history of Earths components, and the processes by which they are shaped.

Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology significantly overlaps all other earth sciences, including hydrology and the atmospheric sciences, and so is treated as one major aspect of integrated earth system science and planetary science.

Mineralogy Scientific study of minerals and mineralised artifacts

Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical properties of minerals and mineralized artifacts. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.

Carbonate minerals Nickel–Strunz 9 ed mineral class number 5

Carbonate minerals are those minerals containing the carbonate ion, CO32−.

Structure and bonding

The carbonate ion is the simplest oxocarbon anion. It consists of one carbon atom surrounded by three oxygen atoms, in a trigonal planar arrangement, with D3h molecular symmetry. It has a molecular mass of 60.01  g/mol and carries a total formal charge of −2. It is the conjugate base of the hydrogen carbonate (bicarbonate) ion, HCO
, which is the conjugate base of H
, carbonic acid.

Oxocarbon anion

In chemistry, an oxocarbon anion is a negative ion consisting solely of carbon and oxygen atoms, and therefore having the general formula C
for some integers x, y, and n.

Oxygen Chemical element with atomic number 8

Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O
. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up almost half of the Earth's crust.

In chemistry, the molar massM is a physical property defined as the mass of a given substance divided by the amount of substance. The base SI unit for molar mass is kg/mol. However, for historical reasons, molar masses are almost always expressed in g/mol.

The Lewis structure of the carbonate ion has two (long) single bonds to negative oxygen atoms, and one short double bond to a neutral oxygen.

Lewis structures, also known as Lewis dot diagrams, Lewis dot formulas,Lewis dot structures, electron dot structures, or Lewis electron dot structures (LEDS), are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. A Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. The Lewis structure was named after Gilbert N. Lewis, who introduced it in his 1916 article The Atom and the Molecule. Lewis structures extend the concept of the electron dot diagram by adding lines between atoms to represent shared pairs in a chemical bond.


This structure is incompatible with the observed symmetry of the ion, which implies that the three bonds are equally long and that the three oxygen atoms are equivalent. As in the case of the isoelectronic nitrate ion, the symmetry can be achieved by a resonance between three structures:

Nitrate anion

Nitrate is a polyatomic ion with the molecular formula NO
and a molecular mass of 62.0049 u. Organic compounds that contain the nitrate ester as a functional group (RONO2) are also called nitrates.

In chemistry, resonance is a way of describing bonding in certain molecules or ions by the combination of several contributing structures into a resonance hybrid in valence bond theory. It has particular value for describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis structure.


This resonance can be summarized by a model with fractional bonds and delocalized charges:

Carbonate-ion-delocalised-partial-charges-2D.png Carbonate-3D-vdW.png

Chemical properties

Metal carbonates generally decompose on heating, liberating carbon dioxide from the long term carbon cycle to the short term carbon cycle and leaving behind an oxide of the metal. [2] This process is called calcination, after calx, the Latin name of quicklime or calcium oxide, CaO, which is obtained by roasting limestone in a lime kiln.

A carbonate salt forms when a positively charged ion, M+
, M2+
, or M3+
, associates with the negatively charged oxygen atoms of the ion by forming electrostatic attractions with them, forming an ionic compound:

2 M+
+ CO2−
+ CO2−
2 M3+
+ 3 CO2−

Most carbonate salts are insoluble in water at standard temperature and pressure, with solubility constants of less than 1 × 10−8. Exceptions include lithium, sodium, potassium and ammonium carbonates, as well as many uranium carbonates.

In 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 bicarbonate ion 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 carbonate is basic, sodium bicarbonate is weakly basic, while carbon dioxide itself is a weak acid.

Carbonated water is 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.

Although the carbonate salts of most metals are insoluble in water, the same is not true of the bicarbonate salts. In solution this equilibrium between carbonate, bicarbonate, carbon dioxide and carbonic acid changes constantly to the changing temperature and pressure conditions. In the case of metal ions with insoluble carbonates, e.g. CaCO3, formation of insoluble compounds results. This is an explanation for the buildup of scale inside pipes caused by hard water.

Carbonate in the Inorganic nomenclature

Systematic additive IUPAC name for carbonate anion is trioxidocarbonate(2−). [1] :127 Similarly, cyanide anion CN is named nitridocarbonate(1−). [1] :291 Following this logic, e.g. carbonate(4−) in the systematic additive nomenclature would mean carbide anion, but it is not the case. [1] :287

Organic carbonates

In organic chemistry a carbonate can also refer to a functional group within a larger molecule that contains a carbon atom bound to three oxygen atoms, one of 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 carbonate and propylene carbonate, and the phosgene replacement, triphosgene.

Biological significance

It works as a buffer in the blood as follows: when pH is low, the concentration of hydrogen ions is too high, so one exhales CO2. This will cause the equation to shift left,[ further explanation needed ] 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 (HCO
). This causes the equation to shift right, essentially increasing the concentration of hydrogen ions, causing a more acidic pH.

Three important reversible reactions control the above pH balance: [3]

  1. H2CO3(aq) H+(aq) + HCO
  1. H2CO3(aq) CO2(aq) + H2O(l)
  1. CO2(aq) CO2(g)

Exhaled CO2(g) depletes CO2(aq), which in turn consumes H2CO3, causing the aforementioned shift left in the first reaction by Le Châtelier's principle. By the same principle, when the pH is too high, the kidneys excrete bicarbonate (HCO
) into urine as urea via the urea cycle (or Krebs–Henseleit ornithine cycle). By removing the bicarbonate, more H+ is generated from carbonic acid (H2CO3), which comes from CO2(g) produced by cellular respiration.

Crucially, this same buffer operates in the oceans. It is a major factor in climate change and the long-term carbon cycle, due to the large number of marine organisms (especially coral) which are formed of calcium carbonate. Increased solubility of carbonate through increased temperatures results in lower production of marine calcite and increased concentration of atmospheric carbon dioxide. This, in turn, increases Earth temperature. The tonnage of CO2−
is on a geological scale and may all be redissolved into the sea and released to the atmosphere, increasing CO2 levels even more.[ citation needed ]

Carbonate salts

H2CO3 He
BeCO3 BC (NH4)2CO3,
Al2(CO3)3 SiPSClAr
ScTiVCr MnCO3 FeCO3 CoCO3 NiCO3 CuCO3 ZnCO3 GaGeAsSeBrKr
Rb2CO3 SrCO3 YZrNbMoTcRuRhPd Ag2CO3 CdCO3 InSnSbTeIXe
BaCO3  HfTaWReOsIrPtAuHg Tl2CO3 PbCO3 (BiO)2CO3 PoAtRn
FrRa RfDbSgBhHsMtDsRgCnNhFlMcLvTsOg
La2(CO3)3 Ce2(CO3)3 PrNdPmSmEuGdTbDyHoErTmYbLu
AcThPa UO2CO3 NpPuAmCmBkCfEsFmMdNoLr

Presence outside Earth

It is generally thought that the presence of carbonates in rock is strong evidence for the presence of liquid water. Recent observations of the planetary nebula NGC 6302 show evidence for carbonates in space, [4] where aqueous alteration similar to that on Earth is unlikely. Other minerals have been proposed which would fit the observations.

Until recently carbonate deposits have not been found on Mars via remote sensing or in situ missions, even though Martian meteorites contain small amounts. Groundwater may have existed at both Gusev [5] and Meridiani Planum. [6]

See also

Related Research Articles

Hydroxide anion

Hydroxide is a diatomic anion with chemical formula OH. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. A hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation (H+), making the parent compound an acid.

Calcium carbonate Chemical compound

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which is a type of sedimentary rock consisting mainly of calcite) and is the main component of pearls and the shells of marine organisms, snails, and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous.

Sodium bicarbonate chemical compound

Sodium bicarbonate (IUPAC name: sodium hydrogen carbonate), commonly known as baking soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation (Na+) and a bicarbonate anion (HCO3). Sodium bicarbonate is a white solid that is crystalline, but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of washing soda (sodium carbonate). The natural mineral form is nahcolite. It is a component of the mineral natron and is found dissolved in many mineral springs.

Sodium carbonate chemical compound

Sodium carbonate, Na2CO3, (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, water-soluble salts. All forms have a strongly alkaline taste and give moderately alkaline solutions in water. Historically it was extracted from the ashes of plants growing in sodium-rich soils. Because the ashes of these sodium-rich plants were noticeably different from ashes of wood (once used to produce potash), sodium carbonate became known as "soda ash". It is produced in large quantities from sodium chloride and limestone by the Solvay process.

The common-ion effect states that in a chemical solution in which several species reversibly associate with each other by an equilibrium process, increasing the concentration of any one of its dissociated components by adding another chemical that also contains it will cause an increased amount of association. This result is a consequence of Le Chatelier's principle for the equilibrium reaction of the association/dissociation. The effect is commonly seen as an effect on the solubility of salts and other weak electrolytes. Adding an additional amount of one of the ions of the salt generally leads to increased precipitation of the salt, which reduces the concentration of both ions of the salt until the solubility equilibrium is reached. The effect is based on the fact that both the original salt and the other added chemical have one ion in common with each other.

Magnesium carbonate chemical compound

Magnesium carbonate, MgCO3 (archaic name magnesia alba), is an inorganic salt that is a white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.

Neutralization (chemistry) chemical reaction

In chemistry, neutralization or neutralisation is a chemical reaction in which an acid and a base react quantitatively with each other. In a reaction in water, neutralization results in there being no excess of hydrogen or hydroxide ions present in the solution. The pH of the neutralized solution depends on the acid strength of the reactants. Neutralization is used in many applications.

Chromate and dichromate anion, CrO₄²⁻, a moderately strong oxidizing agent

Chromate salts contain the chromate anion, CrO2−
. Dichromate salts contain the dichromate anion, Cr
. They are oxoanions of chromium in the 6+ oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.

Limescale hard, off-white, chalky deposit found in kettles, hot-water boilers

Limescale is a hard, off-white, chalky deposit often found in kettles and hot water boilers and on the inside of hot water pipework. It is also often found as a similar deposit on the inner surfaces of old pipes and other surfaces where "hard water" has evaporated.

Metabolic acidosis lactic acidosis that has material basis in high levels of acid

Metabolic acidosis is a condition that occurs when the body produces excessive quantities of acid or when the kidneys are not removing enough acid from the body. If unchecked, metabolic acidosis leads to acidemia, i.e., blood pH is low (less than 7.35) due to increased production of hydrogen ions by the body or the inability of the body to form bicarbonate (HCO3) in the kidney. Its causes are diverse, and its consequences can be serious, including coma and death. Together with respiratory acidosis, it is one of the two general causes of acidemia.

Alkalinity The capacity of water to resist changes in pH that would make the water more acidic

Alkalinity is the capacity of water to resist changes in pH that would make the water more acidic. Alkalinity is the strength of a buffer solution composed of weak acids and their conjugate bases. It is measured by titrating the solution with a monoprotic acid such as HCl until its pH changes abruptly, or it reaches a known endpoint where that happens. Alkalinity is expressed in units of meq/L, which corresponds to the amount of monoprotic acid added as a titrant in millimoles per liter.

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 (HCO
), and carbonate (CO2−
) 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.

Alkali soil soil type

Alkali, or Alkaline, soils are clay soils with high pH, a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and difficult to clarify/settle. They derive their name from the alkali metal group of elements, to which sodium belongs, and which can induce basicity. Sometimes these soils are also referred to as alkaline sodic soils.
Alkaline soils are basic, but not all basic soils are alkaline.

Chloride shift (also known as the Hamburger phenomenon or lineas phenomenon, named after Hartog Jakob Hamburger) is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO3) and chloride (Cl) across the membrane of red blood cells (RBCs).

The dealkalization of water refers to the removal of alkalinity ions from water. Chloride cycle anion ion exchange dealkalizers remove alkalinity from water.

Residual sodium carbonate index

The residual sodium carbonate (RSC) index of irrigation water or soil water is used to indicate the alkalinity hazard for soil. The RSC index is used to find the suitability of the water for irrigation in clay soils which have a high cation exchange capacity. When dissolved sodium in comparison with dissolved calcium and magnesium is high in water, clay soil swells or undergoes dispersion which drastically reduces its infiltration capacity.

Oilfield scale inhibition is the process of preventing the formation of scale from blocking or hindering fluid flow through pipelines, valves, and pumps used in oil production and processing. Scale inhibitors (SIs) are a class of specialty chemicals that are used to slow or prevent scaling in water systems. Oilfield scaling is the precipitation and accumulation of insoluble crystals (salts) from a mixture of incompatible aqueous phases in oil processing systems. Scale is a common term in the oil industry used to describe solid deposits that grow over time, blocking and hindering fluid flow through pipelines, valves, pumps etc. with significant reduction in production rates and equipment damages. Scaling represents a major challenge for flow assurance in the oil and gas industry. Examples of oilfield scales are calcium carbonate (limescale), iron sulfides, barium sulfate and strontium sulfate. Scale inhibition encompasses the processes or techniques employed to treat scaling problems.


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  3. "Archived copy". Archived from the original on 2011-07-21. Retrieved 2010-09-05.CS1 maint: Archived copy as title (link)
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