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.unionised - 27-8-2023 at 03:15
The equilibrium composition won't be equimolar. Sodium sesquicarbonate may very well crystallize as a portion of the equilibrated salt mixture,
however.
