Unravelling the mysteries of carbonic acid
Researchers report the first detailed characterization of the hydration structure of carbonic dioxide gas as it dissolves in water to form carbonic acid.
Though carbonic acid exists for only a fraction of a second, it imparts a lasting impact on Earth’s atmosphere and geology, and on the human body.
Blink your eyes and it’s long gone. Carbonic acid exists for only a tiny fraction of a second when carbon dioxide gas dissolves in water before changing into a mix of protons and bicarbonate anions. Despite its short life, however, carbonic acid imparts a lasting impact on Earth’s atmosphere and geology, as well as on the human body.
However, because of its short lifespan, the detailed chemistry of carbonic acid has long been veiled in mystery. Researchers with Berkeley Lab and the University of California (UC) Berkeley are helping to lift this veil through a series of unique experiments.
In their latest study, they’ve shown how gaseous carbon dioxide molecules are solvated by water to initiate the proton transfer chemistry that produces carbonic acid and bicarbonate.
‘Through a combination of X-ray absorption spectroscopy (XAS), theoretical modeling and computational simulations, we’re able to report the first detailed characterization of the hydration structure of carbon dioxide gas dissolved in water,’ says Richard Saykally, a chemist with Berkeley Lab’s Chemical Sciences Division and professor of chemistry at UC Berkeley who leads this research. ‘Our results will help improve future theoretical modeling of this crucial chemistry by characterizing the initial state of the proton transfer reactions that occur in water.
‘This latest work follows a separate recent study in which the hydration structure of carbonic acid itself was characterized. Ultimately, such studies will lead to a complete understanding of how atmospheric carbon dioxide is captured and transformed by ocean surfaces, a crucial role in the carbon cycle.
They will also enable us to address how bicarbonate anions interact with calcium and magnesium cations in solution to create the nanoclusters that nucleate limestone formation, and how bicarbonate anions buffer blood and other bodily fluids.’
Saykally and his research group have overcome the challenge of carbonic acid’s short lifetime — about 26 milliseconds — by developing a unique liquid microjet mixing technology. In this technology, two aqueous samples rapidly mix and flow through a finely tipped nozzle that is made from fused silica and features an opening only a few micrometers in diameter. The resulting liquid beam is injected into a vacuum chamber and intersected by an X-ray beam before being collected and frozen out.
Saykally and his group installed their liquid microjet system at Berkeley Lab’s Advanced Light Source (ALS), an electron accelerator/storage ring that serves as a premier source of X-ray beams for scientific research. In earlier experiments, they used their microjet system and XAS technique to characterize the hydration structures of aqueous carbonate and bicarbonate.
In this new study, Saykally and his group were able to capture the XAS spectrum of carbon dioxide gas dissolved in water. All of these experiments were performed at ALS Beamline 8.0.1, a high flux undulator beamline that generates X-ray beams optimized for XAS studies.
Saykally and his colleagues determined the hydration structure of carbon dioxide in water by using their XAS spectral data in conjunction with molecular dynamics simulations carried out under the leadership of David Prendergast, a staff scientist in the Theory of Nanostructures Facility at Berkeley Lab’s Molecular Foundry. Calculations were performed utilizing the supercomputer resources of the National Energy Research Scientific Computing Center (NERSC).
The ALS, the Molecular Foundry and NERSC are all national user facilities funded by the U.S. Department of Energy (DOE)’s Office of Science.
The results of this study show that the carbonic acid molecule acts as a hydrophobe with an average hydrogen bond number of 0.56. The carbon atom interacts weakly with the oxygen of a single water molecule at a distance of greater than 2.67 Angstroms, and the carbonyl oxygens serve as weak hydrogen bond acceptors. The result is an enhanced tetrahedral water/hydrogen bonding structure, with a local cylindrical cavity carved out in the water solvent.
‘Calculated spectral energy shifts and intensities between aqueous carbonic acid, dissolved carbon dioxide and gaseous carbon dioxide correspond well with our experimentally measured spectra,’ Saykally says. ‘In future studies, we will focus on resolving some limitations of our current experimental design and the limitations of molecular dynamics modeling through the implementation of higher level ab initio theories.
The results of this latest study have been published as an Editor’s Choice feature article in Chemical Physical Letters. The paper is titled ‘The hydration structure of dissolved carbon dioxide from X-Ray absorption spectroscopy.’ Saykally is the corresponding author. Other co-authors, in addition to Prendergast, are Royce Lam, Alice England, Jacob Smith, Anthony Rizzuto and Orion Shih.
See more here: sciencedaily.com
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Joseph Olson
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Carbon8c Acid, H2CO3 is very weak, unstable acid with a 26 millisecond life outside of test tube. The oceans are at maximum saturation of CO2 gas, transient H2CO3 is never a threat to coral feefs in an ALKALINE ocean with pH range of 7.8 to 8.4 > ocean acidification is another Carbon forcing LIE.
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Artelia
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Washing soda is NaCO3. Is sea water diluted washing soda?
If we have dilutions of H2CO3 in our seas and dilutions of NaCl,
would we not also have dilutions of NaCO3?
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Climate Heretic
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These equations will tear shreds in anyone’s argument that the oceans are becoming more (acidic) sic.
.
CaSiO3 + H2CO3 = CaCO3 + H2O + SiO2
CaCO3 + H2CO3 = Ca(HCO3)2
Regards
Climate Heretic
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Artelia
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Carbonic dioxide is actually known as carbon dioxide.
Carbonic acid is CO2, dissolved in water and we can buy
this to drink in the supermarkets.
So if this is not CH2O3, what is it? It does last for months,
if not years but quickly goes flat once the bottle is opened.
WE have a dilution of carbonic acid in rainwater too.
What is this about it only lasting for seconds?
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Jerry Krause
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Hi PSI Readets.
Until Artella wrote “Carbonic dioxide” (5:14pm) I had not noticed that this article’s author had written “carbonic dioxide gas”. Now, we do not know if this was purposeful or merely a mistake.
However, when Joseph wrote “Carbon8c Acid, H2CO3 is very weak, unstable acid with a 26 millisecond life outside of test tube.”, I (ignoring the 8) believe that he purposefully wrote “26 millisecond life outside of test tube.” So, I, a chemist, have ask Joseph, an engineer, how it is that he knows this?
For I believe that when a carbon dioxide (CO2) molecule dissolves in liquid water that it reacts with a water molecule (H2O) to form the molecule H2CO3 (aq). Which further reacts with another water molecule to dissociate into the ions [H3O^+ (aq)] and [HCO3^- (aq)]. And then the anion [HCO3^- (aq) reacts with another water molecule to form another [H3O^+ (aq)} and {CO3^2- (aq)}. Now the question becomes: In which particle: aqueous (aq) molecule or aqueous anions containing a carbon atom does many more than a billion dissolved carbon dioxide gaseous molecules end up to create a natural sea water solution with a pH range of 7.8 to 8.4 (ALKALINE) and not (ACIDIC—pH less than 7).
The analysis to answer this CHEMICAL EQUILIBRIUM question is well beyond the general purpose of this PSI website. But natural pH range does allow a chemist to conclude that the predominant dissolved particle is H2CO3 (aq).
Have a good day, Jerry
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Joseph Olson
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“….challenging carbonic acid’s short lifetime – ABOUT 26 MILLISECONDS” ~ read the article
(sometimes fat fingers on tiny tablets make a typo or two, get over it)
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Jerry Krause
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Hi Joseph,
I read: “Through a combination of X-ray absorption spectroscopy (XAS), theoretical modeling and computational simulations, we’re able to report the first detailed characterization of the hydration structure of carbon dioxide gas dissolved in water,’ says Richard Saykally, ” The only observed data is the x-ray absorption spectroscopy. So if it completely defines (describes) what is known, what is the need for theoretical modeling and computational simulations??? I have described the only theoretical modeling about which I know.
And I know from experience that a computer only does what it is programed to do. There is no such thing as artificial intelligence. So, I cannot imagine how the molecule H2CO3 (aqueous) can ever escape from the liquid solution in which it was formed.
Have a good day, Jerry
Reply