Carbonate

Carbonate Ion, CO₃^2-

Acid Equilibria:

CO₃^2-(aq) + H₂O(l) <==> HCO₃^-(aq) + OH^-(aq) K_b = 2.0 x 10^-4

HCO₃^-(aq) + H₂O(l) <==> H₂CO₃(aq) + OH^-(aq) K_b = 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.

Solubility:

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

BaCO₃(s) <==> Ba²⁺(aq) + CO₃^2-(aq) K_sp = 5.0 x 10^-9

CaCO₃(s) <==> Ca²⁺(aq) + CO₃^2-(aq) K_sp = 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.

Oxidation-Reduction:

None.

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