SnailsAttack
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Bicarbonate content of sodium carbonate at equilibrium with the atmosphere
Sodium carbonate will absorb water and carbon dioxide from the atmosphere to form sodium bicarbonate, like so:
Na₂CO₃ + CO₂ + H₂O -> 2NaHCO₃
In absence of water vapor and atmospheric CO₂ (particularly at elevated temperatures), the reaction reverses to produce sodium carbonate:
2NaHCO₃ -> Na₂CO₃ + CO₂ + H₂O
Thus the carbonate:bicarbonate ratio of a given dry sample at equilibrium with the atmosphere depends on the temperature and the ambient partial
pressures of CO₂ and H₂O.
For an aqueous solution, the carbonate:bicarbonate ratio depends on the temperature, the ambient partial pressure of CO₂, and the concentration of
the solution (I believe).
What I'd like to know is how one might go about calculating the ratio of carbonate to bicarbonate for a given set of conditions. I'm mostly curious
about this for the purpose of understanding the formation, stability and composition of carbonate evaporite deposits.
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unionised
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I think the eqm is with this stuff
https://en.wikipedia.org/wiki/Sodium_sesquicarbonate
rather than bicarbonate.
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SnailsAttack
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The equilibrium composition won't be equimolar. Sodium sesquicarbonate may very well crystallize as a portion of the equilibrated salt mixture,
however.
[Edited on 8/27/2023 by SnailsAttack]
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