Carbonate Ion, CO32-

 Acid Equilibria:

CO32-(aq) + H2O(l) <==> HCO3-(aq) + OH-(aq) Kb = 2.0 x 10-4

HCO3-(aq) + H2O(l) <==> H2CO3(aq) + OH-(aq) Kb = 2.5 x 10-8

H2CO3(aq) <==> H2O(l) + CO2(g)

Carbonate ion, a moderately strong base, undergoes considerable hydrolysis in aqueous solution. In strongly acidic solution, CO2 gas is evolved.


Carbonate ion can be precipitated from solution as white barium or calcium salts that have low solubilities:

BaCO3(s) <==> Ba2+(aq) + CO32-(aq) Ksp = 5.0 x 10-9

CaCO3(s) <==> Ca2+(aq) + CO32-(aq) Ksp = 7.5 x 10-9

Although many carbonate salts are insoluble, those of Na+, K+, and NH4+ are quite soluble. All bicarbonate (HCO3-) salts are soluble. Because of this, even insoluble carbonate salts dissolve in acid.



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