Marine Science Faculty Publications

Interaction of B(OH)03 and HCO-3 in Seawater: Formation of B(OH)2CO-3

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boron, boric acid, carbonate, CO2 system, complexation, spectrophotometric pH

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Boron is known to interact with a wide variety of protonated ligands(HL) creating complexes of the form B(OH)2L-.Investigation of the interaction of boric acid and bicarbonate in aqueoussolution can be interpreted in terms of the equilibrium


The formation constant for this reaction at 25 °C and 0.7 molkg-1 ionic strength is


where brackets represent the total concentration of each indicatedspecies. This formation constant indicates that theB(OH)2 CO3−">CO−3CO3− concentration inseawater at 25 °C is on the order of 2 μmol kg-1. Dueto the presence of B(OH)2 CO3−">CO−3CO3− , theboric acid dissociation constant (K′B">K′BK′B ) in natural seawaterdiffers from K′B">K′BK′B determined in the absence of bicarbonate byapproximately 0.5%. Similarly, the dissociation constants of carbonicacid and bicarbonate in natural seawater differ from dissociation constantsdetermined in the absence of boric acid by about 0.1%. Thesedifferences, although small, are systematic and exert observable influenceson equilibrium predictions relating CO2 fugacity, pH, totalcarbon and alkalinity in seawater.

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Aquatic Geochemistry, v. 3, p. 345-356