PH of water in limestone

1. Dec 11, 2009

coookiemonste

1. The problem statement, all variables and given/known data
Find the pH of water in limestone (CaCO3) quarry.
H2CO3 pk1=6.37, pk2=10.32

2. Relevant equations
pH=pKa + log [conjugate base]/[acid]
Kw=10^-14

3. The attempt at a solution
CO3 2- + H2O -> HCO3- + OH-
Ka= [HCO3-][OH-]/[CO3 2-]
10^-10.32=x^2/[10^-6.37]
[OH-]=x=.01059
-log[OH-]=1.98
14-1.98=12.02
is this correct?

Last edited: Dec 11, 2009
2. Dec 11, 2009

wallace13

since its a salt, I think you can do pH= 1/2 (pKa1 + pKa2)

3. Dec 12, 2009

Staff: Mentor

No, that would work for solution of amphiprotic salt, here you start with fully neutralized carbonate.

A lot depends on the initial cncentration of carbonates - and this depends on the calcium carbonate solubility product. Besides, solubility will increase due to carbonates hydrolyzis, so finding an exact answer can be tricky. No idea how deep you are expected to get into it.

Why do you think [CO32-] = Ka1?

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