Would you know a relationship that predicts the ratio between CO2 hydration (CO2+H2O -->H2CO3) relative to CO2 hydroxylation (CO2+OH- -->HCO3-) as a function of the solution pH, salinity and temperature? I have the constant of reactions (function of temperature and salinity) for both hydration and hydroxylation from Johnson (1982) but not sure how to get the relative occurrence of these two reactions for a given set of environmental parameters.
I have a set of equations and references relating to this on my webpage
http://www.microcosmofscience.com/CO2%20and%20TIC%20calculator.html
pH, salinity and temperature affect the carbonate dissociation constants K1 and K2. Once these have been computed for the appropriate water type, the ionization fraction (α0, α1, α2) of TIC into H2CO3, HCO3- and CO3-- can be calculated.
The book 'Aquatic Chemistry: Chemical Equilibria and Rates in Natural Waters' by Stumm & Morgan is the go-to reference for this kind of aquatic chemistry.
Thank you Damian, your webpage is very handy.
I am ok with carbonate speciation, I wanted to calculate the ratio between the two reactions that leads to CO2 dissolution in in water. CO2 reacts with H2O only at low pH (hydration) and progressively more with OH- as the pH increases (hydroxylation).
With more reading I found that this ratio can be calculated from the equation of Johnson (1982): K’ = K(CO2), + K(OH) . Kw / [H+]
where K' is the constant of CO2 dissolution, K(CO2) cst of hydration reation, K(OH) cst of hydroxylation, Kw water dissotiation cst
Johnson (1982) provides the equation for each K as function temperature and salinity.
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