Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Uwe on October 13, 2020, 08:24:17 PM
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It is sometimes stated that CaCO3 precipitation in seawater can occur either following
(1) Ca2+ + Co32- -> CaCO3
or
(2) Ca2+ + HCO32- -> CaCO3 + H+
In an abiotic system, in which CaCO3 precipitation only follows thermodynamics, why would CaCO3 precipitation follow equation 2?
It is sometime stated that this would occur as DIC at a the pH range of seawater is mainly composed of HCO32-. But the CaCO3 lattice is composed of Ca2+ and carbonate, not bicarbonate ions, so ultimately the precipitation reaction will again be equation 1
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Think about it this way: first equation refers to the overall process consisting of a dissociation followed by the precipitation.