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Re: [APD] pH at which CaCO3 dissolves



Thanks, Augustine,  I aske dthe question and promise to
write down the answer this time ;-)

Scott H.
--- Augustine Rodriguez <r0dr1gaj at jvlnet_com> wrote:
> 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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