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

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Discussion Overview

The discussion centers around calculating the pH of a solution containing BaCO3 and SrCO3 dissolved in acetic acid, specifically in a scenario where the acetic acid is not in water and half of it is consumed in the reaction. The scope includes theoretical considerations of pH calculation, acid-base reactions, and buffering effects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how to calculate the pH of a non-aqueous solution, specifically with BaCO3 and SrCO3 in acetic acid.
  • Another participant suggests that the acetic acid is likely dissolved in water, implying a potential oversight in the original question.
  • A participant proposes a reaction equation involving carbonate ions and acetic acid, seeking to determine the pH based on the consumption of half the acetic acid.
  • One participant argues that if half of the 4 M acetic acid is consumed, the effective molarity for pH calculation would be 2 M, and mentions the importance of considering the dissociation constant of acetic acid.
  • Another participant introduces the idea that the solution behaves as a buffered system due to the presence of BaCO3 and SrCO3, comparing it to the buffering of aspirin by CaCO3.
  • It is noted that carbonates will decompose in acetic acid, leading to an acetic buffer, but the high ionic strength of the concentrated solution may complicate calculations.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the solution and the implications for pH calculation. There is no consensus on the correct approach to determining the pH in this specific context.

Contextual Notes

Participants highlight potential limitations related to the assumptions made about the solution's composition and the effects of ionic strength on calculations. The discussion remains open regarding the appropriate method for calculating pH in a non-aqueous environment.

broegger
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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?
 
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You are given that the acetic acid is 4 Molar solution, and more likely than not, it is dissolve in water.
 
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.
 
Last edited:
Thanks, man! :-)
 
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, Ksp, 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/
 
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.
 

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