Carbonic acid

Carbonic acid
Structural formula
Structural formula
Ball-and-stick model
Ball-and-stick model
Names
Preferred IUPAC name
Carbonic acid
Other names
  • Oxidocarboxylic acid
  • Hydroxyformic acid
  • Hydroxymethanoic acid
  • Carbonylic acid
  • Hydroxycarboxylic acid
  • Dihydroxycarbonyl
  • Carbon dioxide solution
  • Aerial acid
  • Metacarbonic acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.133.015 Edit this at Wikidata
EC Number
  • 610-295-3
25554
KEGG
UNII
  • InChI=1S/CH2O3/c2-1(3)4/h(H2,2,3,4) checkY
    Key: BVKZGUZCCUSVTD-UHFFFAOYSA-N checkY
  • InChI=1/H2O3/c2-1(3)4/h(H2,2,3,4)
    Key: BVKZGUZCCUSVTD-UHFFFAOYAU
  • O=C(O)O
Properties
H2CO3
Molar mass 62.024 g·mol−1
Appearance Colorless gas
Melting point −53 °C (−63 °F; 220 K) (sublimes)
Boiling point 127 °C (261 °F; 400 K) (decomposes)
Reacts to form carbon dioxide and water
Acidity (pKa)
  • pKa1 = 3.75 (25 °C; anhydrous)
  • pKa1 = 6.35 (hydrous)
  • pKa2 = 10.33
Conjugate base Bicarbonate, carbonate
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 0: Will not burn. E.g. waterInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
0
0
1
Structure
monoclinic
p21/c, No. 14
-
a = 5.392 Å, b = 6.661 Å, c = 5.690 Å
α = 90°, β = 92.66°, γ = 90°
(D2CO3 at 1.85 GPa, 25 °C (298 K))
204.12 Å3
4 formula per cell
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkYX markN ?)

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. In contrast to early-twentieth century textbooks, numerous studies conducted since ca. 1990 identified H2CO3 as a real molecule with a distinct Raman spectrum and with a first-order life-time of ca. 20 ms at 37 °C. More recently, different phases of crystalline hydrated carbonic acid have been obtained at pressures of the order of the GigaPascal . Solid anhydrous carbonic acid has also been isolated.

The interconversion of carbon dioxide and carbonic acid is related to the breathing process of all aerobic organisms and to the acidification of natural waters.

History

In the early days of chemistry, CO2 was known by several names. Led by Lavoisier, a group of chemists systematized the nomenclature of chemicals then known. CO2 was named "carbonic acid" in 1781, because it was produced by the combustion of charcoal (charbon in French), and it was considered an acid. Back then, an acid was something that, when dissolved in water, turned litmus red and had a distinctive acidic taste. Later, chemists reconceptualized "acid", and no longer accepted CO2 to be an acid, and "carbonic acid" became the systematic name of H2CO3 instead. It was thought that H2CO3 could not exist independently, and could only exist in a solution.

In the 1960s, experimenters produced adducts of H2CO3. The diethyl ether adduct H2CO3·O(CH2CH3)2 was prepared at -78 °C. The dimethyl ether adduct H2CO3·O(CH3)2 was synthesized at -30 °C using dimethyl ether and sodium carbonate, and confirmed by chemical, thermochemical, IR, and NMR methods. The pure H2CO3·O(CH3)2 is a solid that decomposes at 5 °C.

In 1987, gaseous H2CO3 was prepared by thermolysis of NH4HCO3, and confirmed by IR and collisional activation mass spectrometry. In 1991, solid H2CO3 was prepared by solid irradiation of a 1:1 H2O + CO2 ice mixture at 20 K (−253.2 °C). The result of this preparation route is termed α−H2CO3. Another synthesis route was to begin by reacting HBr and KHCO3 in an aqueous solution, then sublimate away water at 200 K (−73 °C). Confirmed by FTIR spectroscopy. The result of this preparation route is termed β−H2CO3. However, α−H2CO3 is later argued to be (CH3)O(COOH), a monomethyl ester.

This then leaves the question of why H2CO3 has "surprising kinetic stability", and why it took so long for solid-state H2CO3 to be isolated. An explanation using transition state theory is that pure H2CO3 is in fact rather metastable. At 300 K, its half-life is theoretically predicted to be ~105 years, but in the presence of 2 water molecules, it decreases to ~1 minute. In short, water catalyzes the decomposition of H2CO3.

Anhydrous carbonic acid

According to quantum chemical calculations, at room temperature (300 K), pure carbonic acid is expected to be a kinetically stable gas. There are two main methods to produce anhydrous carbonic acid: reaction of hydrogen chloride and potassium bicarbonate at 100 K in methanol and proton irradiation of pure solid carbon dioxide. Chemically, it behaves as a diprotic Brønsted acid.

Carbonic acid monomers exhibit three conformational isomers: cis–cis, cis–trans, and trans–trans.

At low temperature and atmospheric pressure, solid carbonic acid is amorphous and lacks Bragg peaks in X-ray diffraction. But at high pressure, carbonic acid crystallizes, and modern analytical spectroscopy can measure its geometry, which under certain conditions have space group Cmc21.

According to neutron diffraction of dideuterated carbonic acid (D2CO3) in a hybrid clamped cell (Ni–Cr–Al Russian alloy/copper-beryllium) at 1.85 GPa, the molecules are planar and form dimers joined by pairs of hydrogen bonds. All three C-O bonds are nearly equidistant at 1.34 Å, intermediate between typical C-O and C=O distances (respectively 1.43 and 1.23 Å). The unusual C-O bond lengths are attributed to delocalized 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 Å), through the 136° O-H-O angle imposed by the doubly hydrogen-bonded 8-membered rings. The crystal has space group P21/C. Longer O—O distances are observed in strong intramolecular hydrogen bonds, e.g. in oxalic acid, where the distances exceed 2.4 Å. Trimers and higher polymers are predicted to be even more stable. Based on the stability, it was suggested that solid carbonic acid can be used to sequestrate carbon.

In aqueous solution

In the presence of even a slight amount of water, carbonic acid dehydrates to carbon dioxide and water, which then catalyzes further decomposition.

The hydration equilibrium constant at 25 °C is [H2CO3]/[CO2] ≈ 1.7×10−3 in pure water and ≈ 1.2×10−3 in seawater. Hence the majority of carbon dioxide at geophysical or biological air-water interfaces does not convert to carbonic acid, remaining dissolved CO2 gas. However, the uncatalyzed equilibrium is reached quite slowly: the rate constants are 0.039 s−1 for hydration and 23 s−1 for dehydration.

In biological solutions

In the presence of the enzyme carbonic anhydrase, equilibrium is instead reached rapidly, and the following reaction takes precedence:

HCO3− + H+ ⇌ CO2 + H2O

When the carbon dioxide concentration exceeds its solubility, gas evolves, and a third equilibrium CO2(aq) ⇌ CO2(g) must also be considered. The equilibrium constant for this reaction is defined by Henry's law.

The two reactions can be combined for the equilibrium in solution: HCOA3A−+HA+↽−−⇀COA2(aq)+HA2OK3=[HA+][HCOA3A−][COA2(aq)] 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.

In water pH control

In wastewater treatment and agricultural irrigation, carbonic acid is used to acidify the water, similar to sulfuric acid and sulfurous acid produced by sulfur burners.

Under high CO2 partial pressure

In the beverage industry, sparkling or "fizzy water" is usually referred to as carbonated water. It is made by dissolving carbon dioxide in water under a small positive pressure. Many soft drinks are treated the same way and effervesce.

Significant amounts of molecular H2CO3 exist in aqueous solutions subjected to pressures of multiple gigapascals (tens of thousands of atmospheres) in planetary interiors. Pressures of 0.6–1.6 GPa at 100 K, and 0.75–1.75 GPa at 300 K are attained in the cores of large icy satellites such as Ganymede, Callisto, and Titan, where water and carbon dioxide are present. Pure carbonic acid, being denser than ice, is expected to have sunk beneath the ice layers and separated them from the rocky cores of these moons.

From CO2 clathrate hydrate

Recently, crystalline hydrated carbonic acid was synthesised via a solid-state reaction starting from CO2 clathrate hydrate. The CO2 clathrate hydrate is compressed at a temperature of 130 K up to pressures higher than 4 GPa. During this compression the clathrate undergoes a progressive amorphisation. At 4 GPa, the sample is isobarically heated up to ambient temperature. Carbonic acid molecules appears during the isobaric heating at 190 K and then organise in a hydrated crystal at 280 K. When the isobaric heating is performed above 5 GPa, the temperatures required for the crystallization of the hydrated carbonic acid are higher and crystals with different stoechiometry and symmetry are obtained .

Relationship to bicarbonate and carbonate

Bjerrum plot of speciation for a hypothetical monoprotic acid: AH concentration as a function of the difference between pK and pH

Carbonic acid is the formal Brønsted–Lowry conjugate acid of the bicarbonate anion, stable in alkaline solution. The protonation constants have been measured to great precision, but depend on overall ionic strength I. The two equilibria most easily measured are as follows: COA3A2−+HA+↽−−⇀HCOA3A−β1=[HCOA3A−][HA+][COA3A2−]COA3A2−+2HA+↽−−⇀HA2COA3β2=[HA2COA3][HA+]2[COA3A2−] where brackets indicate the concentration of species. At 25 °C, these equilibria empirically satisfylog⁡(β1)=0.54I2−0.96I+9.93log⁡(β2)=−2.5I2−0.043I+16.07log(β1) decreases with increasing I, as does log(β2). In a solution absent other ions (e.g. I = 0), these curves imply the following stepwise dissociation constants:pK1=log⁡(β2)−log⁡(β1)=6.77pK2=log⁡(β1)=9.93 Direct values for these constants in the literature include pK1 = 6.35 and pK2 - pK1 = 3.49.

To interpret these numbers, note that two chemical species in an acid equilibrium are equiconcentrated when pK = pH. In particular, the extracellular fluid (cytosol) in biological systems exhibits pH ≈ 7.2, so that carbonic acid will be almost 50%-dissociated at equilibrium.

Ocean acidification

Carbonate speciation in seawater (ionic strength 0.7 mol/dm3). The expected change shown is due to the current anthropogenic increase in atmospheric carbon dioxide concentration.

A Bjerrum plot (also known as a Sillén diagram) shows typical equilibrium concentrations of carbon dioxide and its derived species in solution (or seawater) as a function of pH. As human industrialization has 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 acidify those waters, generating a decrease in pH. 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 historical pre-industrial levels.

References

  1. ↑ "Front Matter". Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. pp. 001–4. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
  2. 1 2 W. Hage, K. R. Liedl; Liedl, E.; Hallbrucker, A; Mayer, E (1998). "Carbonic Acid in the Gas Phase and Its Astrophysical Relevance". Science. 279 (5355): 1332–5. Bibcode:1998Sci...279.1332H. doi:10.1126/science.279.5355.1332. PMID 9478889.
  3. 1 2 3 Perrin, D. D., ed. (1984) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon. "Carbonic Acid, H2CO3" entry. ISBN 0-08-029214-3. LCCN 82-16524. {{cite book}}: Check date values in: |year= / |publication-date= mismatch (help)
  4. 1 2 3 4 Benz, Sebastian; Chen, Da; Möller, Andreas; Hofmann, Michael; Schnieders, David; Dronskowski, Richard (September 2022). "The Crystal Structure of Carbonic Acid". Inorganics. 10 (9): 132. doi:10.3390/inorganics10090132. ISSN 2304-6740.
  5. 1 2 3 4 Loerting, Thomas; Tautermann, Christofer; Kroemer, Romano T.; Kohl, Ingrid; Hallbrucker, Andreas; Mayer, Erwin; Liedl, Klaus R.; Loerting, Thomas; Tautermann, Christofer; Kohl, Ingrid; Hallbrucker, Andreas; Erwin, Mayer; Liedl, Klaus R. (2000). "On the Surprising Kinetic Stability of Carbonic Acid (H2CO3)". Angewandte Chemie International Edition. 39 (5): 891–4. doi:10.1002/(SICI)1521-3773(20000303)39:5<891::AID-ANIE891>3.0.CO;2-E. PMID 10760883.
  6. 1 2 3 do Lago, Claudimir Lucio (2024). "A History of Carbonic Acid and the Central Role of Bicarbonate in the CO2/H2O System" (PDF). Química Nova. doi:10.21577/0100-4042.20240038.
  7. ↑ Falcke, H.; Eberle, S.H. (June 1990). "Raman spectroscopic identification of carbonic acid". Water Research. 24 (6): 685–688. Bibcode:1990WatRe..24..685F. doi:10.1016/0043-1354(90)90023-Y.
  8. ↑ Garg, Lal C.; Maren, Thomas H. (January 1972). "The rates of hydration of carbon dioxide and dehydration of carbonic acid at 37°". Biochimica et Biophysica Acta (BBA) - General Subjects. 261 (1): 70–76. doi:10.1016/0304-4165(72)90315-7. PMID 5012475.
  9. ↑ Abramson, Evan H.; Bollengier, Olivier; Brown, J. Michael; Journaux, Baptiste; Kaminsky, Werner; Pakhomova, Anna (1 September 2018). "Carbonic acid monohydrate". American Mineralogist. 103 (9): 1468–1472. Bibcode:2018AmMin.103.1468A. doi:10.2138/am-2018-6554. ISSN 0003-004X.
  10. ↑ Abramson, E. H.; Bollengier, O.; Brown, J. M. (11 April 2017). "Water-carbon dioxide solid phase equilibria at pressures above 4 GPa". Scientific Reports. 7 (1) 821. Bibcode:2017NatSR...7..821A. doi:10.1038/s41598-017-00915-0. ISSN 2045-2322. PMC 5429767. PMID 28400579.
  11. ↑ Berni, Selene; Scelta, Demetrio; Romi, Sebastiano; Fanetti, Samuele; Alabarse, Frederico; Pagliai, Marco; Bini, Roberto (2024). "Exploring High-Pressure Polymorphism in Carbonic Acid through Direct Synthesis from Carbon Dioxide Clathrate Hydrate". Angewandte Chemie International Edition. 63 (22) e202403953. doi:10.1002/anie.202403953. ISSN 1521-3773. PMID 38536217.
  12. ↑ Berni, Selene; Scelta, Demetrio; Romi, Sebastiano; Fanetti, Samuele; Alabarse, Frederico; Wehinger, Bjorn; Bini, Roberto (2025). "Understanding the formation mechanism of crystalline hydrated polymorphs of carbonic acid from CO 2 clathrate hydrate". Chemical Science. 16 (47): 22769–22780. doi:10.1039/D5SC02241J. ISSN 2041-6520. PMC 12577018. PMID 41181234.
  13. ↑ Scelta, Demetrio; Berni, Selene; Romi, Sebastiano; Fanetti, Samuele; Alabarse, Frederico; Bini, Roberto (27 October 2026). "Exceptional thermal stability of carbonic acid-rich very high-density amorphous ice". The Journal of Chemical Physics. 165 (16): 164509. doi:10.1063/5.0347503. ISSN 0021-9606. PMID 42937155.
  14. 1 2 3 Spahr, Dominik; Bayarjargal, Lkhamsuren; Brüning, Lukas; Kovalev, Valentin; Wedek, Lena M.; Bykov, Maxim; Milman, Victor; Giordano, Nico; Winkler, Björn; Bykova, Elena (8 August 2025). "Synthesis and characterization of crystalline polymeric carbonic acid (H2CO3) with sp3-hybridized carbon at elevated pressures". Communications Chemistry. 8 (1) 237. Bibcode:2025CmChe...8..237S. doi:10.1038/s42004-025-01614-y. ISSN 2399-3669. PMC 12334750. PMID 40781154.
  15. ↑ Galinos, Andreas G.; Carotti, Arrigo A. (February 1961). "The Isolation of Etherated Carbonic Acid". Journal of the American Chemical Society. 83 (3): 752. Bibcode:1961JAChS..83..752G. doi:10.1021/ja01464a053. ISSN 0002-7863.
  16. ↑ Gattow, G.; Gerwarth, U. (March 1968). "Über chalkogenocarbonate. XXX. Versuche zur Isolierung der "freien kohlensäure"︁ OC(OH) 2". Zeitschrift für anorganische und allgemeine Chemie. 357 (1–2): 78–91. doi:10.1002/zaac.19683570110. ISSN 0044-2313.
  17. ↑ Terlouw, Johan K.; Lebrilla, Carlito B.; Schwarz, Helmut (April 1987). "Thermolysis of NH4HCO3 —A Simple Route to the Formation of Free Carbonic Acid (H2CO3) in the Gas Phase". Angewandte Chemie International Edition in English. 26 (4): 354–355. doi:10.1002/anie.198703541. ISSN 0570-0833.
  18. ↑ Moore, M.H.; Khanna, R.K. (January 1991). "Infrared and mass spectral studies of proton irradiated H2O + CO2 ice: Evidence for carbonic acid". Spectrochimica Acta Part A: Molecular Spectroscopy. 47 (2): 255–262. Bibcode:1991AcSpA..47..255M. doi:10.1016/0584-8539(91)80097-3.
  19. ↑ Reisenauer, Hans Peter; Wagner, J. Philipp; Schreiner, Peter R. (27 October 2014). "Gas-Phase Preparation of Carbonic Acid and Its Monomethyl Ester". Angewandte Chemie International Edition. 53 (44): 11766–11771. Bibcode:2014ACIE...5311766R. doi:10.1002/anie.201406969. ISSN 1433-7851. PMID 25196920.
  20. 1 2 Pangotra, Dhananjai; Csepei, Lénárd-István; Roth, Arne; Ponce de León, Carlos; Sieber, Volker; Vieira, Luciana (2022). "Anodic production of hydrogen peroxide using commercial carbon materials". Applied Catalysis B: Environmental. 303 120848. Bibcode:2022AppCB.30320848P. doi:10.1016/j.apcatb.2021.120848. S2CID 240250750.
  21. 1 2 Andersen, C. B. (2002). "Understanding carbonate equilibria by measuring alkalinity in experimental and natural systems". Journal of Geoscience Education. 50 (4): 389–403. Bibcode:2002JGeEd..50..389A. doi:10.5408/1089-9995-50.4.389. S2CID 17094010.
  22. 1 2 3 4 Winkel, Katrin; Hage, Wolfgang; Loerting, Thomas; Price, Sarah L.; Mayer, Erwin (1 November 2007). "Carbonic Acid: From Polyamorphism to Polymorphism". Journal of the American Chemical Society. 129 (45): 13863–13871. Bibcode:2007JAChS.12913863W. doi:10.1021/ja073594f. ISSN 0002-7863. PMID 17944463.
  23. ↑ Loerting, Thomas; Bernard, Juergen (2010). "Aqueous Carbonic Acid (H2CO3)". ChemPhysChem. 11 (11): 2305–9. doi:10.1002/cphc.201000220. PMID 20397242.
  24. ↑ Zhao, Yueqi; Tian, Feifei; Sun, Zhaoru (9 May 2025). "Ab initio deep neural network simulations reveal that carbonic acid dissociation is dominated by minority cis-trans conformers". Science Advances. 11 (19) eadu6525. Bibcode:2025SciA...11.6525Z. doi:10.1126/sciadv.adu6525. ISSN 2375-2548. PMC 12057677. PMID 40333980.
  25. ↑ Tossell, J. A. (1 April 2009). "H2CO3(s): A New Candidate for CO2 Capture and Sequestration". Environmental Science & Technology. 43 (7): 2575–2580. Bibcode:2009EnST...43.2575T. doi:10.1021/es802393s. ISSN 0013-936X. PMID 19452919.
  26. ↑ Housecroft, C.E.; Sharpe, A.G. (2005). Inorganic Chemistry (2nd ed.). Prentice-Pearson-Hall. p. 368. ISBN 0-13-039913-2. OCLC 56834315.
  27. ↑ Soli, A. L.; R. H. Byrne (2002). "CO2 system hydration and dehydration kinetics and the equilibrium CO2/H2CO3 ratio in aqueous NaCl solution". Marine Chemistry. 78 (2–3): 65–73. Bibcode:2002MarCh..78...65S. doi:10.1016/S0304-4203(02)00010-5.
  28. ↑ Lindskog S (1997). "Structure and mechanism of carbonic anhydrase". Pharmacology & Therapeutics. 74 (1): 1–20. doi:10.1016/S0163-7258(96)00198-2. PMID 9336012.
  29. ↑ Sander, Rolf; Acree, William E.; Visscher, Alex De; Schwartz, Stephen E.; Wallington, Timothy J. (1 January 2022). "Henry's law constants (IUPAC Recommendations 2021)". Pure and Applied Chemistry. 94 (1): 71–85. Bibcode:2022PApCh..94...71S. doi:10.1515/pac-2020-0302. ISSN 1365-3075.
  30. ↑ Meneses, Adolfo (19 November 2024). "Irrigation water acidification using captured CO2; An option to traditional acidification systems" (PDF). World Ag Expo. Retrieved 19 November 2024.
  31. ↑ Wang, Hongbo; Zeuschner, Janek; Eremets, Mikhail; Troyan, Ivan; Williams, Jonathon (27 January 2016). "Stable solid and aqueous H2CO3 from CO2 and H2O at high pressure and high temperature". Scientific Reports. 6 (1) 19902. Bibcode:2016NatSR...619902W. doi:10.1038/srep19902. PMC 4728613. PMID 26813580.
  32. ↑ Stolte, Nore; Pan, Ding (4 July 2019). "Large presence of carbonic acid in CO2-rich aqueous fluids under Earth's mantle conditions". The Journal of Physical Chemistry Letters. 10 (17): 5135–41. arXiv:1907.01833. Bibcode:2019JPCL...10.5135S. doi:10.1021/acs.jpclett.9b01919. PMID 31411889. S2CID 195791860.
  33. ↑ G. Saleh; A. R. Oganov (2016). "Novel Stable Compounds in the C-H-O Ternary System at High Pressure". Scientific Reports. 6 32486. Bibcode:2016NatSR...632486S. doi:10.1038/srep32486. PMC 5007508. PMID 27580525.
  34. ↑ Berni, Selene; Scelta, Demetrio; Romi, Sebastiano; Fanetti, Samuele; Alabarse, Frederico; Pagliai, Marco; Bini, Roberto (2024). "Exploring High-Pressure Polymorphism in Carbonic Acid through Direct Synthesis from Carbon Dioxide Clathrate Hydrate". Angewandte Chemie International Edition. 63 (22) e202403953. doi:10.1002/anie.202403953. ISSN 1521-3773. PMID 38536217.
  35. ↑ Berni, Selene; Scelta, Demetrio; Romi, Sebastiano; Fanetti, Samuele; Alabarse, Frederico; Wehinger, Bjorn; Bini, Roberto (2025). "Understanding the formation mechanism of crystalline hydrated polymorphs of carbonic acid from CO 2 clathrate hydrate". Chemical Science. 16 (47): 22769–22780. doi:10.1039/D5SC02241J. ISSN 2041-6520. PMC 12577018. PMID 41181234.
  36. ↑ Scelta, Demetrio; Berni, Selene; Romi, Sebastiano; Fanetti, Samuele; Alabarse, Frederico; Bini, Roberto (27 October 2026). "Exceptional thermal stability of carbonic acid-rich very high-density amorphous ice". The Journal of Chemical Physics. 165 (16): 164509. doi:10.1063/5.0347503. ISSN 0021-9606. PMID 42937155.
  37. ↑ IUPAC (2006). "Stability constants" (database).
  38. ↑ Pines, Dina; Ditkovich, Julia; Mukra, Tzach; Miller, Yifat; Kiefer, Philip M.; Daschakraborty, Snehasis; Hynes, James T.; Pines, Ehud (2016). "How Acidic Is Carbonic Acid?". J Phys Chem B. 120 (9): 2440–51. Bibcode:2016JPCB..120.2440P. doi:10.1021/acs.jpcb.5b12428. PMC 5747581. PMID 26862781.
  39. ↑ Caldeira, K.; Wickett, M. E. (2003). "Anthropogenic carbon and ocean pH". Nature. 425 (6956): 365. Bibcode:2001AGUFMOS11C0385C. doi:10.1038/425365a. PMID 14508477. S2CID 4417880.
  40. ↑ Sabine, C. L. (2004). "The Oceanic Sink for Anthropogenic CO2". Science. 305 (5682): 367–371. Bibcode:2004Sci...305..367S. doi:10.1126/science.1097403. hdl:10261/52596. PMID 15256665. S2CID 5607281. Archived from the original on 6 July 2008. Retrieved 22 June 2021.

Further reading