View source for Carbonic acid

{{short description|Chemical compound}}
{{Distinguish|Phenol{{!}}carbolic acid|carboxylic acid}}
{{Redirect|Carbonyl hydroxide|the chemical compound with formula COOH (carbonyl group linked to hydroxyl group)|Carboxylic acid}}
{{Use dmy dates|date=March 2021}}
{{Chembox
| Watchedfields = changed
| verifiedrevid = 477313558
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageFile = 
| ImageFile1 = Carbonic-acid-2D.svg
| ImageName1 = Structural formula
| ImageFile2=Carbonic-acid-3D-balls.png
| ImageName2=Ball-and-stick model
| OtherNames = {{ubl|Oxidocarboxylic acid|Hydroxyformic acid|Hydroxymethanoic acid|Carbonylic acid|Hydroxycarboxylic acid|Dihydroxycarbonyl|Carbon dioxide solution|Aerial acid|Metacarbonic acid}}
| IUPACName = Carbonic acid<ref name=iupac2013>{{cite book |title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book) |publisher=The [[Royal Society of Chemistry]] |date=2014 |location=Cambridge |pages=P001–4 |doi=10.1039/9781849733069-FP001 |isbn=978-0-85404-182-4 |chapter=Front Matter}}</ref>
| PIN = 
| SystematicName = 
| Section1 = {{Chembox Identifiers
| CASNo = 463-79-6
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 142M471B3J
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 28976
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 1161632
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 747
| DrugBank = DB14531
| EC_number = 610-295-3
| Gmelin = 25554
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C01353
| PubChem = 767
| InChI = 1/H2O3/c2-1(3)4/h(H2,2,3,4)
| InChIKey = BVKZGUZCCUSVTD-UHFFFAOYAU
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/CH2O3/c2-1(3)4/h(H2,2,3,4)
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = BVKZGUZCCUSVTD-UHFFFAOYSA-N
| SMILES = O=C(O)O
}}
| Section2 = {{Chembox Properties
| Appearance = Colorless gas
| Formula = {{chem|H|2|CO|3}}
| ConjugateBase = [[Bicarbonate]], [[carbonate]]
| pKa = {{ubl|p''K''<sub>a1</sub> {{=}} 3.75 (25 °C; anhydrous)<ref name=P82db>{{cite book|title=Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution|editor-first=D.&nbsp;D.|editor-last=Perrin|edition=2nd|series=[[IUPAC]] Chemical Data|issue=29|publisher=Pergamon|location=Oxford|year=1982|publication-date=1984|orig-date=1969|lccn=82-16524|isbn=0-08-029214-3|at="Carbonic Acid, H<sub>2</sub>CO<sub>3</sub>" entry}}</ref>|p''K''<sub>a1</sub> {{=}} 6.35 (hydrous)<ref name=P82db/>|p''K''<sub>a2</sub> {{=}} 10.33<ref name=P82db/>}}
| MeltingPtC = -53
| MeltingPt_ref = <ref name="sublime">{{cite journal |last1=W. Hage |first1=K. R. Liedl |last2=Liedl |first2=E. |title=Carbonic Acid in the Gas Phase and Its Astrophysical Relevance |journal=[[Science (journal)|Science]] |volume=279 |pages=1332–5
 |year=1998 |doi=10.1126/science.279.5355.1332 |pmid=9478889 |last3=Hallbrucker |first3=A |last4=Mayer |first4=E |issue=5355| bibcode=1998Sci...279.1332H}}</ref>
| MeltingPt_notes = (sublimes)
| BoilingPtC = 127
| BoilingPt_notes = (decomposes)
| BoilingPt_ref = 
| Solubility = Reacts to form [[carbon dioxide]] and [[water]]
 }}
| Section3 = {{Chembox Hazards
| NFPA-H = 0
| NFPA-F = 0
| NFPA-R = 1
}}
| Section4 = {{Chembox Structure
| Structure_ref = 
| CrystalStruct = monoclinic
| SpaceGroup = p21/c, No. 14
| PointGroup = -
| LattConst_a = 5.392 Å
| LattConst_b = 6.661 Å
| LattConst_c = 5.690 Å
| LattConst_alpha = 
| LattConst_beta = 92.66
| LattConst_gamma = 
| LattConst_Comment = ({{chem|D|2|CO|3}} at 1.85 GPa, 298 K)
| LattConst_ref = <ref name=neutron>{{cite journal |last1=Benz |first1=Sebastian |last2=Chen |first2=Da |last3=Möller |first3=Andreas |last4=Hofmann |first4=Michael |last5=Schnieders |first5=David |last6=Dronskowski |first6=Richard |title=The Crystal Structure of Carbonic Acid |journal=[[Inorganics]] |date=September 2022 |volume=10 |issue=9 |pages=132 |language=en |issn=2304-6740 |doi=10.3390/inorganics10090132 |doi-access=free}}</ref>
| UnitCellVolume = 204.12 Å<sup>3</sup>
| UnitCellFormulas = 4 formula per cell
| Coordination = 
| MolShape = 
| OrbitalHybridisation = 
| Dipole = 
 }}
| Section5 = 
| Section6 = 
}}

'''Carbonic acid''' is a [[chemical compound]] with the chemical formula {{chem2|H2CO3|auto=on}}. 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]].<ref>{{Greenwood&Earnshaw2nd|page=310}}</ref><ref name="lo">{{cite journal |last1=Loerting |first1=Thomas |author1-link=Thomas Loerting |last2=Tautermann |first2=Christofer |last3=Kroemer |first3=Romano T. |last4=Kohl |first4=Ingrid |last5=Hallbrucker |first5=Andreas |last6=Mayer |first6=Erwin |last7=Liedl |first7=Klaus R. |last8=Loerting |first8=Thomas |last9=Tautermann |first9=Christofer |last10=Kohl |first10=Ingrid |last11=Hallbrucker |first11=Andreas |last12=Erwin |first12=Mayer |last13=Liedl |first13=Klaus R. |date=2000 |title=On the Surprising Kinetic Stability of Carbonic Acid (H<sub>2</sub>CO<sub>3</sub>) |journal=Angewandte Chemie International Edition |volume=39 |issue=5 |pages=891–4 |doi=10.1002/(SICI)1521-3773(20000303)39:5<891::AID-ANIE891>3.0.CO;2-E |pmid=10760883}}</ref> The interconversion of carbon dioxide and carbonic acid is related to the breathing cycle of animals and the [[ocean acidification|acidification of natural waters]].<ref name=neutron/>

In biochemistry and physiology, the name "carbonic acid" is sometimes applied to [[properties of water|aqueous solution]]s of [[carbon dioxide]]. These [[chemical species]] play an important role in the [[bicarbonate buffer system]], used to maintain [[acid–base homeostasis]].<ref>[https://www.anaesthesiamcq.com/AcidBaseBook/ab2_1.php Acid-Base Physiology 2.1 – Acid-Base Balance] by Kerry Brandis.</ref>

==Terminology in biochemical literature==
In [[chemistry]], the term "carbonic acid" strictly refers to the [[chemical compound]] with the formula {{chem|H|2|CO|3}}. Some [[biochemistry]] literature effaces the distinction between carbonic acid and carbon dioxide dissolved in extracellular fluid. 

In [[physiology]], carbon dioxide excreted by the [[lungs]] may be called ''volatile acid'' or ''respiratory acid''.

==Anhydrous carbonic acid==
At ambient temperatures, pure carbonic acid is a stable gas.<ref name="lo" /> There are two main methods to produce [[anhydrous]] carbonic acid: reaction of [[hydrogen chloride]] and [[potassium bicarbonate]] at [[Orders of magnitude (temperature)|100&nbsp;K]] in [[methanol]] and [[Proton beam|proton irradiation]] of pure [[solid carbon dioxide]].<ref name="sublime" /> Chemically, it behaves as a [[diprotic acid|diprotic]] [[Brønsted acid]].<ref name=peroxide /><ref name="Andersen" />

Carbonic acid [[monomers]] exhibit three [[conformational isomerism|conformational isomers]]: cis–cis, cis–trans, and trans–trans.<ref>{{cite journal |author1=Loerting, Thomas |author2=Bernard, Juergen |year=2010 |title=Aqueous Carbonic Acid (H<sub>2</sub>CO<sub>3</sub>) |journal=ChemPhysChem |issue=11 |pages=2305–9 |doi=10.1002/cphc.201000220}}</ref>

At low temperatures and [[atmospheric pressure]], solid carbonic acid is [[Amorphous solid|amorphous]] and lacks [[Bragg peak|Bragg peaks]] in [[X-ray diffraction]].<ref name="wi">{{cite journal |last1=Winkel |first1=Katrin |last2=Hage |first2=Wolfgang |last3=Loerting |first3=Thomas |last4=Price |first4=Sarah L. |last5=Mayer |first5=Erwin |date=2007 |title=Carbonic Acid: From Polyamorphism to Polymorphism |journal=Journal of the American Chemical Society |volume=129 |issue=45 |pages=13863–71 |doi=10.1021/ja073594f |pmid=17944463}}</ref> But at high pressure, carbonic acid crystallizes, and modern analytical spectroscopy can measure its geometry.

According to [[neutron diffraction]] of [[deuterium|dideuterated]] carbonic acid ({{chem|D|2|CO|3}}) in a [[hybrid clamped cell]] ([[Russian alloy]]/[[Copper beryllium alloy|copper-beryllium]]) at 1.85&nbsp;GPa, the molecules are planar and form [[Dimerization (chemistry)|dimers]] joined by pairs of [[hydrogen bond]]s. All three [[Carbon–oxygen bond|C-O bonds]] are nearly equidistant at 1.34&nbsp;[[Angstrom|Å]], intermediate between typical C-O and C=O distances (respectively 1.43 and 1.23&nbsp;Å). The unusual C-O bond lengths are attributed to delocalized [[Pi bond|π bonding]] in the molecule's center and extraordinarily strong hydrogen bonds. The same effects also induce a very short O—O separation (2.13&nbsp;Å), through the 136° O-H-O [[angle]] imposed by the doubly hydrogen-bonded 8-membered rings.<ref name="neutron" /> Longer O—O distances are observed in strong intramolecular hydrogen bonds, e.g. in [[oxalic acid]], where the distances exceed 2.4&nbsp;Å.<ref name="wi" />

==In aqueous solution==
In even a slight presence of water, carbonic acid [[Dehydration reaction|dehydrates]] to [[carbon dioxide]] and [[water]], which then [[Autocatalysis|catalyzes]] further decomposition.<ref name="lo" /> For this reason, carbon dioxide can be considered the carbonic [[Acidic oxide|acid anhydride]].

The [[hydrate|hydration]] [[equilibrium constant]] at 25&nbsp;°C is {{awrap|[{{chem|H|2|CO|3}}]/[{{CO2}}]&nbsp;≈ 1.7×10<sup>−3</sup>}} in pure water<ref name="HS">{{cite book |last1=Housecroft |first1=C.E. |title=Inorganic Chemistry |last2=Sharpe |first2=A.G. |date=2005 |publisher=Prentice-Pearson-Hall |isbn=0-13-039913-2 |edition=2nd |page=368 |oclc=56834315}}</ref> and ≈&nbsp;1.2×10<sup>−3</sup> in [[seawater]].<ref name="SB">{{cite journal |last=Soli |first=A. L. |author2=R. H. Byrne |year=2002 |title=CO<sub>2</sub> system hydration and dehydration kinetics and the equilibrium CO<sub>2</sub>/H<sub>2</sub>CO<sub>3</sub> ratio in aqueous NaCl solution |journal=Marine Chemistry |volume=78 |issue=2–3 |pages=65–73 |doi=10.1016/S0304-4203(02)00010-5}}</ref> Hence the majority of carbon dioxide at geophysical or biological [[Surface water|air-water interfaces]] does not convert to carbonic acid, remaining dissolved {{CO2}} gas. However, the [[catalyst|uncatalyzed]] equilibrium is reached quite slowly: the [[rate constant]]s are 0.039&nbsp;[[Second|s]]<sup>−1</sup> for hydration and 23&nbsp;s<sup>−1</sup> for dehydration.

===In biological solutions===
In the presence of the enzyme [[carbonic anhydrase]], equilibrium is instead reached rapidly, and the following reaction takes precedence:<ref name="Lindskog_1997">{{cite journal |vauthors=Lindskog S |year=1997 |title=Structure and mechanism of carbonic anhydrase |journal=Pharmacology & Therapeutics |volume=74 |issue=1 |pages=1–20 |doi=10.1016/S0163-7258(96)00198-2 |pmid=9336012}}</ref> <chem display=block>HCO3^- {+} H^+ <=> CO2 {+} H2O</chem>

When the created carbon dioxide exceeds its solubility, gas evolves and a third equilibrium <chem display=block>CO_2 (soln) <=> CO_2 (g)</chem> must also be taken into consideration. The equilibrium constant for this reaction is defined by [[Henry's law#Fundamental types and variants of Henry's law constants|Henry's law]]. 

The two reactions can be combined for the equilibrium in solution: <math chem="" display="block">\begin{align}
\ce{HCO3^{-}{} + H+{} <=> CO2(soln){} + H2O} && K_3 = \frac{[\ce{H+}][\ce{HCO3^-}]}{[\ce{CO2(soln)}]}
\end{align}</math> When Henry's law is used to calculate the denominator '''care is needed''' with regard to units since Henry's law constant can be commonly expressed with 8 different dimensionalities.<ref>{{Cite journal |last=Sander |first=Rolf |last2=Acree |first2=William E. |last3=Visscher |first3=Alex De |last4=Schwartz |first4=Stephen E. |last5=Wallington |first5=Timothy J. |date=2022-01-01 |title=Henry’s law constants (IUPAC Recommendations 2021) |url=https://www.degruyter.com/document/doi/10.1515/pac-2020-0302/html |journal=Pure and Applied Chemistry |language=en |volume=94 |issue=1 |pages=71–85 |doi=10.1515/pac-2020-0302 |issn=1365-3075|doi-access=free}}</ref>

=== In water pH control ===
In wastewater treatment and agriculture irrigation, carbonic acid is used to acidify the water similar to [[sulfuric acid]] and [[sulfurous acid]] produced by sulfur burners.<ref>{{Cite web |last=Meneses |first=Adolfo |date=November 19, 2024 |title=Irrigation water acidification using captured CO2; An option to traditional acidification systems. |url=https://www.worldagexpo.com/wp-content/uploads/sites/2/2020/11/Soil-acidification-r.-1.0.pdf |access-date=November 19, 2024 |website=World Ag Expo}}</ref>

=== Under high CO<sub>2</sub> partial pressure ===
In the [[beverage industry]], sparkling or "fizzy water" is usually referred to as [[carbonated water]]. It is made by dissolving carbon dioxide under a small [[positive pressure]] in water. Many [[soft drink]]s treated the same way [[effervescent|effervesce]].

Significant amounts of molecular {{chem|H|2|CO|3}} exist in aqueous solutions subjected to pressures of multiple [[Gigapascal|gigapascals]] (tens of thousands of atmospheres) in planetary interiors.<ref>{{cite journal |last1=Wang |first1=Hongbo |last2=Zeuschner |first2=Janek |last3=Eremets |first3=Mikhail |last4=Troyan |first4=Ivan |last5=Williams |first5=Jonathon |date=27 January 2016 |title=Stable solid and aqueous H<sub>2</sub>CO<sub>3</sub> from CO<sub>2</sub> and H<sub>2</sub>O at high pressure and high temperature |journal=Scientific Reports |volume=6 |issue=1 |page=19902 |bibcode=2016NatSR...619902W |doi=10.1038/srep19902 |pmc=4728613 |pmid=26813580 |doi-access=free}}</ref><ref>{{cite journal |last1=Stolte |first1=Nore |last2=Pan |first2=Ding |date=4 July 2019 |title=Large presence of carbonic acid in CO<sub>2</sub>-rich aqueous fluids under Earth's mantle conditions |journal=The Journal of Physical Chemistry Letters |volume=10 |issue=17 |pages=5135–41 |arxiv=1907.01833 |doi=10.1021/acs.jpclett.9b01919 |pmid=31411889 |s2cid=195791860}}</ref> Pressures of 0.6–1.6&nbsp;[[gigapascal|GPa]] at 100&nbsp;[[kelvin|K]], and 0.75–1.75&nbsp;GPa at 300&nbsp;K are attained in the cores of large icy satellites such as [[Ganymede (moon)|Ganymede]], [[Callisto (moon)|Callisto]], and [[Titan (moon)|Titan]], where water and carbon dioxide are present. Pure carbonic acid, being denser, is expected to have sunk under the ice layers and separate them from the rocky cores of these moons.<ref name="Saleh-Scirep">{{cite journal |author1=G. Saleh |author2=A. R. Oganov |date=2016 |title=Novel Stable Compounds in the C-H-O Ternary System at High Pressure |journal=Scientific Reports |volume=6 |page=32486 |bibcode=2016NatSR...632486S |doi=10.1038/srep32486 |pmc=5007508 |pmid=27580525}}</ref>

== Relationship to bicarbonate and carbonate ==
[[File:Weak acid speciation.svg|thumb|right|[[Bjerrum plot]] of speciation for a hypothetical monoprotic acid: AH concentration as a function of the difference between {{Math|''p''K}} and {{Math|''p''H}}]]
Carbonic acid is the formal [[Brønsted–Lowry]] [[conjugate acid]] of the [[bicarbonate]] anion, stable in [[Base (chemistry)|alkaline solution]]. The protonation constants have been measured to great precision, but depend on overall [[ionic strength]] {{Mvar|I}}. The two equilibria most easily measured are as follows: <math chem display="block">\begin{align}
\ce{CO3^{2-}{} + H+{} <=> HCO3^-} && \beta_1 = \frac{[\ce{HCO3^-}]}{[\ce{H+}][\ce{CO3^{2-}}]} \\
\ce{CO3^{2-}{} + 2H+{} <=> H2CO3} && \beta_2 = \frac{[\ce{H2CO3}]}{[\ce{H+}]^2[\ce{CO3^{2-}}]}
\end{align}</math> where brackets indicate the [[concentration]] of [[Species (chemistry)|species]]. At 25&nbsp;°C, these equilibria empirically satisfy<ref>[[IUPAC]] (2006). "[https://old.iupac.org/publications/scdb/index.html Stability constants]" (database). </ref><math display="block">\begin{alignat}{6}
\log(\beta_1) =&& 0&.54&I^2 - 0&.96&I +&& 9&.93 \\
\log(\beta_2) =&& -2&.5&I^2 - 0&.043&I +&& 16&.07
\end{alignat}</math>{{Math|log(''&beta;''<sub>1</sub>)}} decreases with increasing {{Mvar|I}}, as does {{Math|log(''&beta;''<sub>2</sub>)}}. In a solution absent other ions (e.g. {{Math|''I'' {{=}} 0}}), these curves imply the following [[Dissociation constant|stepwise dissociation constants]]:<math display="block">\begin{alignat}{3}
p\text{K}_1 &= \log(\beta_2) - \log(\beta_1) &= 6.77 \\
p\text{K}_2 &= \log(\beta_1) &= 9.93
\end{alignat}</math> Direct values for these constants in the literature include {{math|''p''K<sub>1</sub> {{=}} 6.35}} and {{math|''p''K<sub>2</sub> - ''p''K<sub>1</sub> {{=}} 3.49}}.<ref>{{cite journal |last1=Pines |first1=Dina |last2=Ditkovich |first2=Julia |last3=Mukra |first3=Tzach |last4=Miller |first4=Yifat |last5=Kiefer |first5=Philip M. |last6=Daschakraborty |first6=Snehasis |last7=Hynes |first7=James T. |last8=Pines |first8=Ehud |date=2016 |title=How Acidic Is Carbonic Acid? |journal=J Phys Chem B |volume=120 |issue=9 |pages=2440–51 |doi=10.1021/acs.jpcb.5b12428 |pmc=5747581 |pmid=26862781}}</ref>

To interpret these numbers, note that two chemical species in an acid equilibrium are [[Equinumerosity|equiconcentrated]] when {{Math|''p''K {{=}} ''p''H}}. In particular, the [[extracellular fluid]] ([[cytosol]]) in biological systems exhibits {{Math|''p''H &approx; 7.2}}, so that carbonic acid will be almost 50%-dissociated at equilibrium.

=== Ocean acidification ===
[[File:Carbonate system of seawater.svg|thumb|upright=1.4|Carbonate speciation in seawater (ionic strength 0.7&nbsp;mol/dm<sup>3</sup>). The expected change shown is due to the [[Greenhouse gas emissions|current anthropogenic increase]] in [[atmospheric carbon dioxide]] concentration.|left]]

The [[Bjerrum plot]] shows typical equilibrium concentrations, in solution, in [[seawater]], of carbon dioxide and the various species derived from it, as a function of [[pH]].<ref name="peroxide">{{cite journal |last1=Pangotra |first1=Dhananjai |last2=Csepei |first2=Lénárd-István |last3=Roth |first3=Arne |last4=Ponce de León |first4=Carlos |last5=Sieber |first5=Volker |last6=Vieira |first6=Luciana |year=2022 |title=Anodic production of hydrogen peroxide using commercial carbon materials |journal=Applied Catalysis B: Environmental |volume=303 |page=120848 |doi=10.1016/j.apcatb.2021.120848 |s2cid=240250750}}</ref><ref name="Andersen">{{cite journal |last=Andersen |first=C. B. |year=2002 |title=Understanding carbonate equilibria by measuring alkalinity in experimental and natural systems |journal=Journal of Geoscience Education |volume=50 |issue=4 |pages=389–403 |doi=10.5408/1089-9995-50.4.389 |bibcode=2002JGeEd..50..389A |s2cid=17094010}}</ref> As human industrialization has [[Greenhouse gas emissions|increased the proportion]] of [[carbon dioxide in Earth's atmosphere]], the proportion of carbon dioxide dissolved in sea- and freshwater as carbonic acid is also expected to increase. This rise in dissolved acid is also expected to [[Acidifying agent|acidify]] those waters, generating a decrease in pH.<ref name="cald03">{{cite journal |last=Caldeira |first=K. |author2=Wickett, M. E. |title=Anthropogenic carbon and ocean pH |journal=[[Nature (journal) |Nature]] |volume=425 |issue=6956 |pages=365 |year=2003 |s2cid=4417880 |pmid=14508477 |bibcode=2001AGUFMOS11C0385C |doi=10.1038/425365a |doi-access=free |url=https://zenodo.org/record/1233227}}</ref><ref name="sabine">{{cite journal |last=Sabine |first=C. L. |year=2004 |title=The Oceanic Sink for Anthropogenic CO<sub>2</sub> |journal=Science |volume=305 |issue=5682 |pages=367–371 |pmid=15256665 |bibcode=2004Sci...305..367S |hdl=10261/52596 |hdl-access=free |s2cid=5607281 |doi=10.1126/science.1097403 |url=https://www.science.org/doi/abs/10.1126/science.1097403 |access-date=22 June 2021 |url-status=live |archive-url=https://web.archive.org/web/20080706143710/http://www.sciencemag.org/cgi/content/short/305/5682/367 |archive-date=6 July 2008}}</ref> It has been estimated that the increase in dissolved carbon dioxide has already caused the ocean's average surface pH to decrease by about 0.1 from pre-industrial levels.

==Further reading==
*{{WsPSM2|Climate and Carbonic Acid|59|July 1901}}
*{{cite journal |last1=Welch |first1=M. J. |last2=Lifton |first2=J. F. |last3=Seck |first3=J. A. |title=Tracer studies with radioactive oxygen-15. Exchange between carbon dioxide and water |journal=[[J. Phys. Chem.]] |volume=73 |issue=335 |year=1969 |page=3351 |doi=10.1021/j100844a033}}
*{{cite book |last=Jolly |first=W. L. |title=Modern Inorganic Chemistry |edition=2nd|publisher=McGraw-Hill |year=1991 |isbn=978-0-07-112651-9}}
*{{cite journal |last1=Moore |first1=M. H. |last2=Khanna |first2=R. |title=Infrared and Mass Spectral Studies of Proton Irradiated H<sub>2</sub>O+CO<sub>2</sub> Ice: Evidence for Carbonic Acid Ice: Evidence for Carbonic Acid |journal=[[Spectrochimica Acta Part A |Spectrochimica Acta]] |volume=47A |pages=255–262 |year=1991 |issue=2 |bibcode=1991AcSpA..47..255M |doi=10.1016/0584-8539(91)80097-3 |url=https://zenodo.org/record/1258549}}
*{{cite journal |last1=W. Hage |first1=K. R. Liedl |last2=Liedl |first2=E. |last3=Hallbrucker |first3=A |last4=Mayer |first4=E |title=Carbonic Acid in the Gas Phase and Its Astrophysical Relevance |journal=[[Science (journal)|Science]] |volume=279 |pages=1332–5 |year=1998 |pmid=9478889 |issue=5355 |bibcode=1998Sci...279.1332H |doi=10.1126/science.279.5355.1332}}
*{{cite journal |last1=Hage |first1=W. |last2=Hallbrucker |first2=A. |last3=Mayer |first3=E. |title=A Polymorph of Carbonic Acid and Its Possible Astrophysical Relevance |journal=[[J. Chem. Soc. Faraday Trans.]] |volume=91 |pages=2823–6 |year=1995 |issue=17 |bibcode=1995JCSFT..91.2823H |doi=10.1039/ft9959102823}}

{{clear}}

==References==
<references />

==External links==
*[http://www.iq.usp.br/gutz/Curtipot_.html Carbonic acid/bicarbonate/carbonate equilibrium in water: pH of solutions, buffer capacity, titration, and species distribution vs. pH, computed with a free spreadsheet]
*[https://web.archive.org/web/20091018082042/http://www.chem.usu.edu/~sbialkow/Classes/3600/Overheads/Carbonate/CO2.html How to calculate concentration of carbonic acid in water]

{{Inorganic compounds of carbon}}
{{Carbonates}}
{{Hydrogen compounds}}
{{Oxides of carbon}}

{{Authority control}}
[[Category:Carbonates]]
[[Category:Carboxylic acids]]
[[Category:Inorganic carbon compounds]]
[[Category:Mineral acids]]