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[APD] pH at which CaCO3 dissolves

The question came up: at what pH does CaCO3 dissolve?

Here is a quick calculation:

Equations used:

CO3-- <-----> HCO3- + OH-
H2CO3 <-----> H+ + HCO3-

The solubility product constant of CaCO3 is 8.7x10^-9. Therefore, the
concentration of CO3-- is 9.3x10^-5M at saturation.

The 1st dissociation constant of carbonic acid is 4.3x10^-7. Therefore,
4.3x10^-7 x 9.3x10^-5M = [HCO3-][OH-]. Therefore, [OH-]=6.3x10^-6 and
pOH=5.2 and pH=8.8

At what pH does CaCO3 dissolve? pH=8.8

Hope this helps.
Augustine Rodriguez
McFarland, WI USA

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