Carbonate

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Carbonate
Carbonate-ion-localised-2D.png
Carbonate anion
Carbonate-ion-delocalised-partial-charges-2D.png
Resonant structure of the carbonate anion
Carbonate-3D-balls.png
Carbonate anion
   Carbon, C
   Oxygen, O
Names
Preferred IUPAC name
Carbonate
Systematic IUPAC name
Trioxidocarbonate [1] : 127 
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
UNII
  • InChI=1S/CH2O3/c2-1(3)4/h(H2,2,3,4)/p-2
    Key: BVKZGUZCCUSVTD-UHFFFAOYSA-L
  • InChI=1/CH2O3/c2-1(3)4/h(H2,2,3,4)/p-2
    Key: BVKZGUZCCUSVTD-NUQVWONBAE
  • C(=O)([O-])[O-]
Properties
CO2−3
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).

A carbonate is a salt of carbonic acid, H2CO3, [2] characterized by the presence of the carbonate ion, a polyatomic ion with the formula CO2−3. The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate groupO=C(−O−)2.

Contents

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.

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, CO2−3. 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"), Na2CO3, and potassium carbonate ("potash"), K2CO3, have been used since antiquity for cleaning and preservation, as well as for the manufacture of glass. Carbonates are widely used in industry, such as in iron smelting, as a raw material for Portland cement and lime manufacture, in the composition of ceramic glazes, and more. New applications of alkali metal carbonates include: thermal energy storage, [3] [4] catalysis [5] and electrolyte both in fuel cell technology [6] as well as in electrosynthesis of H2O2 in aqueous media. [7]

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 hydrogencarbonate (bicarbonate) [8] ion, HCO−3, which is the conjugate base of H2CO3, carbonic acid.

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 atom.

Carbonate-ion-localised-2D.png

This structure is incompatible with the observed symmetry of the ion, which implies that the three bonds are the same length 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 among three structures:

Carbonate-ion-resonance-2D.png

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

Stalactites and stalagmites are carbonate minerals. Labeled speleothems (cropped).jpg
Stalactites and stalagmites are carbonate minerals.

Metal carbonates generally decompose on heating, liberating carbon dioxide 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:

CaCO3 → CaO + CO2

As illustrated by its affinity for Ca2+, carbonate is a ligand for many metal cations. Transition metal carbonate and bicarbonate complexes feature metal ions covalently bonded to carbonate in a variety of bonding modes.

Lithium, sodium, potassium, rubidium, caesium, and ammonium carbonates are water-soluble salts, but carbonates of 2+ and 3+ ions are often poorly soluble in water. Of the insoluble metal carbonates, CaCO3 is important because, in the form of scale, it accumulates in and impedes flow through pipes. Hard water is rich in this material, giving rise to the need for infrastructural water softening.

Acidification of carbonates generally liberates carbon dioxide:

CaCO3 + 2 HCl → CaCl2 + CO2 + H2O

Thus, scale can be removed with acid.

In solution the equilibrium between carbonate, bicarbonate, carbon dioxide and carbonic acid is sensitive to pH, temperature, and pressure. Although di- and trivalent carbonates have low solubility, bicarbonate salts are far more soluble. This difference is related to the disparate lattice energies of solids composed of mono- vs dianions, as well as mono- vs dications.

In aqueous solution, carbonate, bicarbonate, carbon dioxide, and carbonic acid participate 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.

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 R−O−C(=O)−O−R′, or RR′CO3. Important organocarbonates include dimethyl carbonate, the cyclic compounds ethylene carbonate and propylene carbonate, and the phosgene replacement, triphosgene.

Buffer

Three reversible reactions control the pH balance of blood and act as a buffer to stabilise it in the range 7.37–7.43: [9] [10]

  1. H+ + HCO−3 ⇌ H2CO3
  2. H2CO3 ⇌ CO2(aq) + H2O
  3. CO2(aq) ⇌ CO2(g)

Exhaled CO2(g) depletes CO2(aq), which in turn consumes H2CO3, causing the equilibrium of the first reaction to try to restore the level of carbonic acid by reacting bicarbonate with a hydrogen ion, an example of Le Châtelier's principle. The result is to make the blood more alkaline (raise pH). By the same principle, when the pH is too high, the kidneys excrete bicarbonate (HCO−3) 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. [11]

Crucially, a similar 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 made 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 amount of CO2−3 available is on a geological scale and substantial quantities may eventually be redissolved into the sea and released to the atmosphere, increasing CO2 levels even more. [12]

Carbonate salts

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, [13] 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 Gusev [14] and Meridiani Planum. [15]

See also

Related Research Articles

<span class="mw-page-title-main">Acid</span> Chemical compound giving a proton or accepting an electron pair

An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid.

<span class="mw-page-title-main">Acid–base reaction</span> Chemical reaction between an acid and a base

In chemistry, an acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be used to determine pH via titration. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called the acid–base theories, for example, Brønsted–Lowry acid–base theory.

<span class="mw-page-title-main">Bicarbonate</span> Polyatomic 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−
3.

<span class="mw-page-title-main">Carbon dioxide</span> Chemical compound with formula CO₂

Carbon dioxide is a chemical compound with the chemical formula CO2. It is made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature, and as the source of available carbon in the carbon cycle, atmospheric CO2 is the primary carbon source for life on Earth. In the air, carbon dioxide is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas. Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. When carbon dioxide dissolves in water, it forms carbonate and mainly bicarbonate, which causes ocean acidification as atmospheric CO2 levels increase.

<span class="mw-page-title-main">Hydroxide</span> Chemical compound

Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single 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. The corresponding electrically neutral compound HO• is the hydroxyl radical. The corresponding covalently bound group –OH of atoms is the hydroxy group. Both the hydroxide ion and hydroxy group are nucleophiles and can act as catalysts in organic chemistry.

Carbon compounds are defined as chemical substances containing carbon. More compounds of carbon exist than any other chemical element except for hydrogen. Organic carbon compounds are far more numerous than inorganic carbon compounds. In general bonds of carbon with other elements are covalent bonds. Carbon is tetravalent but carbon free radicals and carbenes occur as short-lived intermediates. Ions of carbon are carbocations and carbanions are also short-lived. An important carbon property is catenation as the ability to form long carbon chains and rings.

<span class="mw-page-title-main">Calcium carbonate</span> Chemical compound

Calcium carbonate is a chemical compound with the chemical formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls. Materials containing much calcium carbonate or resembling it are described as calcareous. Calcium carbonate is the active ingredient in agricultural lime and is produced when calcium ions in hard water react with carbonate ions to form limescale. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues.

<span class="mw-page-title-main">Carbonic acid</span> Chemical compound

Carbonic acid is a chemical compound with the chemical formula H2CO3. The molecule rapidly converts to water and carbon dioxide in the presence of water. However, in the absence of water, it is quite stable at room temperature. The interconversion of carbon dioxide and carbonic acid is related to the breathing cycle of animals and the acidification of natural waters.

<span class="mw-page-title-main">Base (chemistry)</span> Type of chemical substance

In chemistry, there are three definitions in common use of the word "base": Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rouelle in the mid-18th century.

<span class="mw-page-title-main">Sodium carbonate</span> Chemical compound

Sodium carbonate is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water. Historically, it was extracted from the ashes of plants grown in sodium-rich soils, and because the ashes of these sodium-rich plants were noticeably different from ashes of wood, sodium carbonate became known as "soda ash". It is produced in large quantities from sodium chloride and limestone by the Solvay process, as well as by carbonating sodium hydroxide which is made using the Chlor-alkali process.

<span class="mw-page-title-main">Magnesium carbonate</span> Chemical compound

Magnesium carbonate, MgCO3, is an inorganic salt that is a colourless or white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.

A hydrogen ion is created when a hydrogen atom loses an electron. A positively charged hydrogen ion (or proton) can readily combine with other particles and therefore is only seen isolated when it is in a gaseous state or a nearly particle-free space. Due to its extremely high charge density of approximately 2×1010 times that of a sodium ion, the bare hydrogen ion cannot exist freely in solution as it readily hydrates, i.e., bonds quickly. The hydrogen ion is recommended by IUPAC as a general term for all ions of hydrogen and its isotopes. Depending on the charge of the ion, two different classes can be distinguished: positively charged ions and negatively charged ions.

The Solvay process or ammonia–soda process is the major industrial process for the production of sodium carbonate (soda ash, Na2CO3). The ammonia–soda process was developed into its modern form by the Belgian chemist Ernest Solvay during the 1860s. The ingredients for this are readily available and inexpensive: salt brine (from inland sources or from the sea) and limestone (from quarries). The worldwide production of soda ash in 2005 was estimated at 42 million tonnes, which is more than six kilograms (13 lb) per year for each person on Earth. Solvay-based chemical plants now produce roughly three-quarters of this supply, with the remaining being mined from natural deposits. This method superseded the Leblanc process.

The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere, biosphere, lithosphere and the hydrosphere. The pedosphere is the foundation of terrestrial life on Earth.

<span class="mw-page-title-main">Alkalinity</span> Capacity of water to resist changes in pH that would make the water more acidic

Alkalinity (from Arabic: القلوية, romanized: al-qaly, lit. 'ashes of the saltwort') is the capacity of water to resist acidification. It should not be confused with basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength of a buffer solution composed of weak acids and their conjugate bases. It is measured by titrating the solution with an acid such as HCl until its pH changes abruptly, or it reaches a known endpoint where that happens. Alkalinity is expressed in units of concentration, such as meq/L (milliequivalents per liter), μeq/kg (microequivalents per kilogram), or mg/L CaCO3 (milligrams per liter of calcium carbonate). Each of these measurements corresponds to an amount of acid added as a titrant.

Calcium bicarbonate, also called calcium hydrogencarbonate, has the chemical formula Ca(HCO3)2. The term does not refer to a known solid compound; it exists only in aqueous solution containing calcium (Ca2+), bicarbonate (HCO−
3), and carbonate (CO2−
3) 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.

<span class="mw-page-title-main">Dissolved inorganic carbon</span> Sum of inorganic carbon species in a solution

Dissolved inorganic carbon (DIC) is the sum of the aqueous species of inorganic carbon in a solution. Carbon compounds can be distinguished as either organic or inorganic, and as dissolved or particulate, depending on their composition. Organic carbon forms the backbone of key component of organic compounds such as – proteins, lipids, carbohydrates, and nucleic acids.

<span class="mw-page-title-main">Alkali soil</span> Soil type with pH > 8.5

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.

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.

<span class="mw-page-title-main">Total inorganic carbon</span> Sum of the inorganic carbon species

Total inorganic carbon is the sum of the inorganic carbon species.

References

  1. ↑ International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN   0-85404-438-8. Electronic version.
  2. 1 2 Chisholm, Hugh, ed. (1911). "Carbonates"  . Encyclopædia Britannica (11th ed.). Cambridge University Press.
  3. ↑ Navarrete, N.; Nithiyanantham, U.; Hernández, L.; Mondragón, R. (2022-03-01). "K2CO3–Li2CO3 molten carbonate mixtures and their nanofluids for thermal energy storage: An overview of the literature". Solar Energy Materials and Solar Cells. 236: 111525. doi:10.1016/j.solmat.2021.111525. hdl: 10234/196651 . ISSN   0927-0248. S2CID   245455194.
  4. ↑ Lambrecht, Mickaël; García-Martín, Gustavo; de Miguel, María Teresa; Lasanta, María Isabel; Pérez, Francisco Javier (2023-08-01). "Temperature dependence of high-temperature corrosion on nickel-based alloy in molten carbonates for concentrated solar power applications". Corrosion Science. 220: 111262. Bibcode:2023Corro.22011262L. doi: 10.1016/j.corsci.2023.111262 . ISSN   0010-938X.
  5. ↑ Hayakawa, Mamiko; Tashiro, Kenshiro; Sumiya, Daiki; Aoyama, Tadashi (2023-06-18). "Simple methods for the synthesis of N -substituted acryl amides using Na 2 CO 3 /SiO 2 or NaHSO 4 /SiO 2". Synthetic Communications. 53 (12): 883–892. doi:10.1080/00397911.2023.2201454. ISSN   0039-7911. S2CID   258197818.
  6. ↑ Milewski, Jarosław; Wejrzanowski, Tomasz; Fung, Kuan-Zong; Szczśniak, Arkadiusz; Ćwieka, Karol; Tsai, Shu-Yi; Dybiński, Olaf; Skibiński, Jakub; Tang, Jhih-Yu; Szabłowski, Łukasz (2021-04-21). "Supporting ionic conductivity of Li2CO3/K2CO3 molten carbonate electrolyte by using yttria stabilized zirconia matrix". International Journal of Hydrogen Energy. International Workshop of Molten Carbonates & Related Topics 2019 (IWMC2019). 46 (28): 14977–14987. doi:10.1016/j.ijhydene.2020.12.073. ISSN   0360-3199. S2CID   234180559.
  7. ↑ Anodic generation of hydrogen peroxide in continuous flow, DOI: 10.1039/D2GC02575B (Paper) Green Chem., 2022, 24, 7931-7940
  8. ↑ Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005 (PDF), IUPAC, p. 137, archived (PDF) from the original on 2017-05-18
  9. ↑ "Chemical of the Week -- Biological Buffers". Archived from the original on 2011-07-21. Retrieved 2010-09-05.
  10. ↑ Acid–Base Regulation and Disorders at The Merck Manual of Diagnosis and Therapy Professional Edition
  11. ↑ Silverthorn, Dee Unglaub (2016). Human physiology. An integrated approach (Seventh, Global ed.). Harlow, England: Pearson. pp. 607–608, 666–673. ISBN   978-1-292-09493-9.
  12. ↑ IPCC (2019). "Summary for Policymakers" (PDF). IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. pp. 3–35.
  13. ↑ Kemper, F., Molster, F.J., Jager, C. and Waters, L.B.F.M. (2001) The mineral composition and spatial distribution of the dust ejecta of NGC 6302. Astronomy & Astrophysics394, 679–690.
  14. ↑ Squyres, S. W.; et al. (2007). "Pyroclastic Activity at Home Plate in Gusev Crater, Mars" (PDF). Science. 316 (5825): 738–742. Bibcode:2007Sci...316..738S. doi:10.1126/science.1139045. hdl: 2060/20070016011 . PMID   17478719. S2CID   9687521. Archived (PDF) from the original on 2017-09-22.
  15. ↑ Squyres, S. W.; et al. (2006). "Overview of the Opportunity Mars Exploration Rover Mission to Meridiani Planum: Eagle Crater to Purgatory Ripple" (PDF). Journal of Geophysical Research: Planets. 111 (E12): n/a. Bibcode:2006JGRE..11112S12S. doi: 10.1029/2006JE002771 . hdl:1893/17165. Archived (PDF) from the original on 2017-08-08.
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