Editing Module:Carbonate

{{short description|Salt or ester of carbonic acid}}
{{about||organic carbonates|Carbonate ester|the town in Colorado|Carbonate, Colorado}}
{{distinguish|Carbon trioxide}}

{{Chembox
| ImageFile1 = Carbonate-ion-localised-2D.png
| ImageCaption1 = Carbonate anion
| ImageClass1 = skin-invert-image
| ImageFile2 = Carbonate-ion-delocalised-partial-charges-2D.png
| ImageCaption2 = [[Resonance (chemistry)|Resonant]] structure of the carbonate [[anion]]
| ImageClass2 = skin-invert-image
| ImageFile3 = Carbonate-3D-balls.png
| ImageAlt3 = Ball-and-stick model of the carbonate anion
| ImageCaption3 = Carbonate anion{{legend|rgb(64, 64, 64)|[[Carbon]], C}}{{legend|red|[[Oxygen]], O}}
| PIN = Carbonate
| SystematicName = Trioxidocarbonate<ref name="redbook">{{RedBookRef}}</ref>{{rp|127}}
| OtherNames =
| Section1 = {{Chembox Identifiers
| CASNo = 3812-32-6
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 7UJQ5OPE7D
| PubChem = 19660
| ChemSpiderID = 18519
| InChI = 1/CH2O3/c2-1(3)4/h(H2,2,3,4)/p-2
| InChIKey = BVKZGUZCCUSVTD-NUQVWONBAE
| StdInChI = 1S/CH2O3/c2-1(3)4/h(H2,2,3,4)/p-2
| StdInChIKey = BVKZGUZCCUSVTD-UHFFFAOYSA-L
| SMILES = C(=O)([O-])[O-]}}
| Section2 = {{Chembox Properties
| Formula = {{chem2|CO3(2-)}}
| C=1|O=3
| ConjugateAcid = [[Bicarbonate]]
| Appearance =
| Solubility = }}
| Section7 = {{Chembox Hazards
| MainHazards =
 }}
}}

A '''carbonate''' is a [[salt (chemistry)|salt]] of [[carbonic acid]], ({{chem2|H2CO3}}),<ref name=EB1911>{{cite EB1911|wstitle=Carbonates}}</ref> characterized by the presence of the '''carbonate ion''', a [[polyatomic ion]] with the formula {{chem2|CO3(2-)}}. The word "carbonate" may also refer to a [[carbonate ester]], an organic compound containing the '''carbonate group''' {{chem2|O\dC(\sO\s)2}}.

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{{snd}}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, {{chem2|CO3(2-)}}. Carbonate minerals are extremely varied and ubiquitous in chemically precipitated [[sedimentary rock]]. The most common are [[calcite]] or [[calcium carbonate]], {{chem2|CaCO3}}, the chief constituent of [[limestone]] (as well as the main component of [[mollusc]] shells and [[coral]] skeletons); [[Dolomite (mineral)|dolomite]], a calcium-magnesium carbonate {{chem2|CaMg(CO3)2}}; and [[siderite]], or [[iron(II) carbonate]], {{chem2|FeCO3}}, an important [[iron ore]]. [[Sodium carbonate]] ("soda" or "natron"), {{chem2|Na2CO3}}, and [[potassium carbonate]] ("potash"), {{chem2|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 (mineral)|lime]] manufacture, in the composition of [[ceramic glaze]]s, and more. New applications of alkali metal carbonates include: thermal energy storage,<ref>{{Cite journal |last1=Navarrete |first1=N. |last2=Nithiyanantham |first2=U. |last3=Hernández |first3=L. |last4=Mondragón |first4=R. |date=2022-03-01 |title=K2CO3–Li2CO3 molten carbonate mixtures and their nanofluids for thermal energy storage: An overview of the literature |url=https://www.sciencedirect.com/science/article/pii/S0927024821005614 |journal=Solar Energy Materials and Solar Cells |volume=236 |pages=111525 |doi=10.1016/j.solmat.2021.111525 |s2cid=245455194 |issn=0927-0248|hdl=10234/196651 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Lambrecht |first1=Mickaël |last2=García-Martín |first2=Gustavo |last3=de Miguel |first3=María Teresa |last4=Lasanta |first4=María Isabel |last5=Pérez |first5=Francisco Javier |date=2023-08-01 |title=Temperature dependence of high-temperature corrosion on nickel-based alloy in molten carbonates for concentrated solar power applications |journal=Corrosion Science |volume=220 |pages=111262 |doi=10.1016/j.corsci.2023.111262 |issn=0010-938X|doi-access=free|bibcode=2023Corro.22011262L }}</ref> catalysis<ref>{{Cite journal |last1=Hayakawa |first1=Mamiko |last2=Tashiro |first2=Kenshiro |last3=Sumiya |first3=Daiki |last4=Aoyama |first4=Tadashi |date=2023-06-18 |title=Simple methods for the synthesis of N -substituted acryl amides using Na 2 CO 3 /SiO 2 or NaHSO 4 /SiO 2 |url=https://www.tandfonline.com/doi/full/10.1080/00397911.2023.2201454 |journal=Synthetic Communications |language=en |volume=53 |issue=12 |pages=883–892 |doi=10.1080/00397911.2023.2201454 |s2cid=258197818 |issn=0039-7911}}</ref> and electrolyte both in fuel cell technology<ref>{{Cite journal |last1=Milewski |first1=Jarosław |last2=Wejrzanowski |first2=Tomasz |last3=Fung |first3=Kuan-Zong |last4=Szczśniak |first4=Arkadiusz |last5=Ćwieka |first5=Karol |last6=Tsai |first6=Shu-Yi |last7=Dybiński |first7=Olaf |last8=Skibiński |first8=Jakub |last9=Tang |first9=Jhih-Yu |last10=Szabłowski |first10=Łukasz |date=2021-04-21 |title=Supporting ionic conductivity of Li2CO3/K2CO3 molten carbonate electrolyte by using yttria stabilized zirconia matrix |url=https://www.sciencedirect.com/science/article/pii/S0360319920346383 |journal=International Journal of Hydrogen Energy |series=International Workshop of Molten Carbonates & Related Topics 2019 (IWMC2019) |volume=46 |issue=28 |pages=14977–14987 |doi=10.1016/j.ijhydene.2020.12.073 |s2cid=234180559 |issn=0360-3199}}</ref> as well as in electrosynthesis of [[Hydrogen peroxide|{{chem2|H2O2}}]] in aqueous media.<ref>Anodic generation of hydrogen peroxide in continuous flow, DOI: 10.1039/D2GC02575B (Paper) Green Chem., 2022, '''24''', 7931–7940</ref>

==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 ''D''<sub>3h</sub> [[Molecular symmetry#Point Group|molecular symmetry]]. It has a molecular mass of 60.01&nbsp;[[Molar mass|g/mol]] and carries a total [[formal charge]] of −2. It is the [[conjugate acid|conjugate base]] of the [[bicarbonate|hydrogencarbonate (bicarbonate)]]<ref>{{Citation |url = http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf |title = Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005 |publisher = IUPAC |page = 137 |url-status = live |archive-url = https://web.archive.org/web/20170518230415/http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf |archive-date = 2017-05-18}}</ref> ion, {{chem2|HCO3-}}, which is the conjugate base of {{chem2|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.

:[[File:Carbonate-ion-localised-2D.png|100px|Simple, localised Lewis structure of the carbonate ion|class=skin-invert-image]]

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 (chemistry)|resonance]] among three structures:

:[[File:Carbonate-ion-resonance-2D.png|400px|Resonance structures of the carbonate ion|class=skin-invert-image]]

This resonance can be summarized by a model with fractional bonds and [[delocalization|delocalized]] charges:

:[[File:Carbonate-ion-delocalised-partial-charges-2D.png|120px|Delocalisation and partial charges on the carbonate ion|class=skin-invert-image]] [[File:Carbonate-3D-vdW.png|80px|Space-filling model of the carbonate ion]]

==Chemical properties==
[[image:Labeled speleothems (cropped).jpg|right|thumb|190px|Stalactites and stalagmites are carbonate minerals.]]
Metal carbonates generally decompose on heating, liberating carbon dioxide leaving behind an oxide of the metal.<ref name=EB1911/> 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]]:
:{{chem2|CaCO3 → CaO + CO2}}
As illustrated by its affinity for {{chem2|Ca(2+)}}, 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 carbonate|Lithium]], [[sodium carbonate|sodium]], [[potassium carbonate|potassium]], [[rubidium carbonate|rubidium]], [[caesium carbonate|caesium]], and [[ammonium carbonate|ammonium]] carbonates are water-soluble salts, but carbonates of 2+ and 3+ ions are often poorly soluble in water. Of the insoluble metal carbonates, [[calcium carbonate|{{chem2|CaCO3}}]] is important because, in the form of [[limescale|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]]:
:{{chem2|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 energy|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 [[chemical equilibrium|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]], {{chem2|CO2(aq)}}, is the main form, which, with water, {{chem2|H2O}}, is in equilibrium with carbonic acid{{snd}}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==
{{main|Carbonate ester}}
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 {{chem2|R\sO\sC(\dO)\sO\sR′}}, or {{chem2|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 solution|buffer]] to stabilise it in the range 7.37–7.43:<ref>{{cite web |url=http://www.scifun.org/chemweek/BioBuff/BioBuffers.html |title=Chemical of the Week -- Biological Buffers |access-date=2010-09-05 |url-status=dead |archive-url=https://web.archive.org/web/20110721174437/http://www.scifun.org/chemweek/BioBuff/BioBuffers.html |archive-date=2011-07-21}}</ref><ref>{{MerckManual|12|157|a||Acid–Base Regulation and Disorders}}</ref>

# {{chem2|H+ + HCO3- ⇌ H2CO3}}
# {{chem2|H2CO3 ⇌ CO2(aq) + H2O}}
# {{chem2|CO2(aq) ⇌ CO2(g)}}

Exhaled {{chem2|CO2(g)}} depletes {{chem2|CO2(aq)}}, which in turn consumes {{chem2|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 ({{chem2|HCO3-}}) into urine as urea via the [[urea cycle]] (or Krebs–Henseleit ornithine cycle). By removing the bicarbonate, more {{chem2|H+}} is generated from carbonic acid ({{chem2|H2CO3}}), which comes from {{chem2|CO2(g)}} produced by [[cellular respiration]].<ref>{{cite book |last1= Silverthorn |first1= Dee Unglaub |title= Human physiology. An integrated approach |edition= Seventh, Global |year= 2016 |publisher= Pearson |location=Harlow, England |isbn=978-1-292-09493-9 |pages= 607–608, 666–673}}</ref>

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 {{chem2|CO3(2-)}} available is on a geological scale and substantial quantities may eventually be redissolved into the sea and released to the atmosphere, increasing {{chem2|CO2}} levels even more.<ref>{{cite book |ref={{harvid|IPCC SROCC Summary for Policymakers|2019}} |chapter=Summary for Policymakers |chapter-url=https://www.ipcc.ch/site/assets/uploads/sites/3/2019/11/03_SROCC_SPM_FINAL.pdf |author=IPCC |author-link=IPCC |year=2019 |title=IPCC Special Report on the Ocean and Cryosphere in a Changing Climate |pages=3–35}}</ref>

==Carbonate salts==
{{see also|Category:Carbonates}}
* Carbonate overview:
{{Carbonates}}

==Presence outside Earth==
It is generally thought that the presence of carbonates in [[Rock (geology)|rock]] is strong evidence for the presence of liquid water. Recent observations of the [[planetary nebula]] [[NGC 6302]] show evidence for carbonates in space,<ref>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 & Astrophysics'' '''394''', 679–690.</ref> where aqueous alteration similar to that on Earth is unlikely. Other minerals have been proposed which would fit the observations.

Small amounts of [[Carbonates on Mars|carbonate deposits]] have been found on Mars via spectral imaging <ref>{{Cite journal |last1=Fairén |first1=Alberto G. |last2=Fernández-Remolar |first2=David |last3=Dohm |first3=James M. |last4=Baker |first4=Victor R. |last5=Amils |first5=Ricardo |date=September 2004 |title=Inhibition of carbonate synthesis in acidic oceans on early Mars |url=https://www.nature.com/articles/nature02911 |journal=Nature |volume=431 |issue=7007 |pages=423–426 |doi=10.1038/nature02911 |pmid=15386004 |bibcode=2004Natur.431..423F |issn=1476-4687}}</ref> and Martian meteorites also contain small amounts. Groundwater may have existed at [[Gusev crater|Gusev]]<ref>{{Cite journal |last1=Squyres |first1=S. W. |last2=Aharonson |first2=O. |last3=Clark |first3=B.C. |last4=Cohen |first4=B. A. |last5=Crumpler |first5=L. |last6=De Souza |first6=P. A. |last7=Farrand |first7=W. H. |last8=Gellert |first8=R. |last9=Grant |first9=J. |display-authors=1 |year=2007 |title=Pyroclastic Activity at Home Plate in Gusev Crater, Mars |journal=Science |volume=316 |issue=5825 |pages=738–742 |bibcode=2007Sci...316..738S |doi=10.1126/science.1139045 |pmid=17478719 |last10=Grotzinger |first10=J. P. |last11=Haldemann |first11=A. F. C. |last12=Johnson |first12=J. R. |last13=Klingelhofer |first13=G. |last14=Lewis |first14=K. W. |last15=Li |first15=R. |last16=McCoy |first16=T. |last17=McEwen |first17=A. S. |last18=McSween |first18=H. Y. |last19=Ming |first19=D. W. |last20=Moore |first20=J. M. |last21=Morris |first21=R. V. |last22=Parker |first22=T. J. |last23=Rice |first23=J. W. |last24=Ruff |first24=S. |last25=Schmidt |first25=M. |last26=Schroder |first26=C. |last27=Soderblom |first27=L. A. |last28=Yen |first28=A.|url=https://authors.library.caltech.edu/36849/7/Squyres.SOM.pdf |archive-url=https://web.archive.org/web/20170922134035/http://authors.library.caltech.edu/36849/7/Squyres.SOM.pdf |archive-date=2017-09-22 |url-status=live |hdl=2060/20070016011 |s2cid=9687521 |hdl-access=free}}</ref> and [[Meridiani Planum]].<ref>{{Cite journal |last1=Squyres |first1=S. W. |last2=Arvidson |first2=R. E. |last3=Bollen |first3=D. |last4=Bell |first4=J. F. |last5=Brückner |first5=J. |last6=Cabrol |first6=N. A. |last7=Calvin |first7=W. M. |last8=Carr |first8=M. H. |last9=Christensen |first9=P. R. |display-authors=1 |year=2006 |title=Overview of the Opportunity Mars Exploration Rover Mission to Meridiani Planum: Eagle Crater to Purgatory Ripple |journal=Journal of Geophysical Research: Planets |volume=111 |issue=E12 |bibcode=2006JGRE..11112S12S |doi=10.1029/2006JE002771 |last10=Clark |first10=B. C. |last11=Crumpler |first11=L. |last12=Des Marais |first12=D. J. |last13=d'Uston |first13=C. |last14=Economou |first14=T. |last15=Farmer |first15=J. |last16=Farrand |first16=W. H. |last17=Folkner |first17=W. |last18=Gellert |first18=R. |last19=Glotch |first19=T. D. |last20=Golombek |first20=M. |last21=Gorevan |first21=S. |last22=Grant |first22=J. A. |last23=Greeley |first23=R. |last24=Grotzinger |first24=J. |last25=Herkenhoff |first25=K. E. |last26=Hviid |first26=S. |last27=Johnson |first27=J. R. |last28=Klingelhöfer |first28=G. |last29=Knoll |first29=A. H. |last30=Landis |first30=G.|pages=n/a |url=http://dspace.stir.ac.uk/bitstream/1893/17165/1/Squyres2006_Overview_of_the_Opportunity_Mars_Exploration_Rover_Mission_to_Meridiani_Planum-Eagle_Crater_to_Purgatory_Ripple.pdf |archive-url=https://web.archive.org/web/20170808163157/http://dspace.stir.ac.uk/bitstream/1893/17165/1/Squyres2006_Overview_of_the_Opportunity_Mars_Exploration_Rover_Mission_to_Meridiani_Planum-Eagle_Crater_to_Purgatory_Ripple.pdf |archive-date=2017-08-08 |url-status=live |hdl=1893/17165 |doi-access=free}}</ref>

==See also==
* [[Cap carbonate]]s
* [[Orthocarbonic acid]], {{chem2|H4CO4}}, or {{chem2|C(OH)4}}, a hypothetic unstable molecule
* [[Oxalate]]
* [[Peroxocarbonate]]
* [[Sodium percarbonate]]

== References ==
{{reflist}}

==External links==
{{Commons category|Carbonates}}
* [http://www2.iq.usp.br/docente/gutz/Curtipot_.html Carbonate/bicarbonate/carbonic acid equilibrium in water: pH of solutions, buffer capacity, titration and species distribution vs. pH computed with a free spreadsheet]
* {{cite encyclopedia|title=Carbonate|url=http://dictionary.reference.com/browse/carbonate|dictionary=Dictionary.com|access-date=5 April 2014}}

{{Oxides of carbon}}
{{Carbon compounds}}
{{Authority control}}

[[Category:Carbonates| ]]
[[Category:Carbon oxyanions]]
[[Category:Oxocarbon anions]]