Calculate the pH-value of a solution that does not contain water

[broegger]

Hi,

How do one calculate the pH-value of a solution that does not contain water, pH being equal to -log([H3O+])?

I need to calculate the pH-value of a solution where BaCO3 and SrCO3 is dissolved in acetic acid (4 M). The only information I am given is, that half of the acetic acid is consumed in the reaction. Any hints?

 

[mrjeffy321]

You are given that the acetic acid is 4 Molar solution, and more likely than not, it is dissolve in water.

 

[broegger]

Ok, I see. The reaction is this (right?):

CO3^2- + CH3COOH -> HCO3^- CH3COO^-​

How can I determine pH? All I know is that half of the CH3COOH is used up in this reaction.

 

[Astronuc]

If one can calculate the pH of an acetic acid solution based on Molarity, it would seem that if one has 4 M acetic acid, and half the acid is used, then the effective Molarity is 2 M. Then one calculates the pH based on 2 M acetic acid. Also, think of the dissociation constant of acetic acid.

http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/pH-strong-acid-dilution.shtml

 

[broegger]

Thanks, man! :-)

 

[Astronuc]

It would appear that the addition of BaCO₃ and SrCO₃ with acetic acid is a buffered solution, much the same as CaCO₃ would buffer aspirin (acetylsalicylic acid).

The solubility constants, K_sp, of BaCO₃ and SrCO₃ are much lower, 8.1 x 10^-9 and 1.6 x 10^-9, than the 1.754 x 10^-5 at 25°C.

Here are two more references for acid-base solutions and pH.
http://www.science.uwaterloo.ca/~cchieh/cact/c123/buffer.html
http://www.shodor.org/unchem/basic/ab/

 

[Borek]

Carbonates will decompose in acetic acid. You will be left with acetic buffer.

Although in so concentrated solution ionic strength is too high for any serious calculations.