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Topic: pH calculation lectures - comments welcomed  (Read 7357 times)

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Offline Borek

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pH calculation lectures - comments welcomed
« on: June 23, 2005, 06:44:03 PM »
For anybody interested in pH calculation some lectures and some questions:

http://www.chembuddy.com/?left=pH-calculation&right=toc

I will be adding questions, no plans about changes in lectures (unless there will be some mistake crying for correction).
« Last Edit: June 23, 2005, 06:51:05 PM by Borek »
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hannibal

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Re:pH calculation lectures - comments welcomed
« Reply #1 on: June 25, 2005, 01:35:52 AM »
i have a solution containing ethanol,water,acetic acid and ethyl acetate(basically an esterification reaction mixture). is there any software online which can find the ph of this solution.
one very crude method would be to find the dissociation of acetic acid in water and in alcohol ,assuming them to be separate mixture find H+ in each and then add the H+ of each mixture to get the total amount of H+ present. from this we can get the pH....but i dont know how accurate it is,pls help me out

Offline Borek

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Re:pH calculation lectures - comments welcomed
« Reply #2 on: June 25, 2005, 07:31:39 AM »
Idea of adding H+ concentrations seems wrong to me, but that's only intuition. No idea how to do the calculations, never heard of such programs (but then I have spent last 20 years farfrom chemistry). Whenever I see information about experiments done in mixed solvents pH is measured, not calculated, and to obtain correct pH acid or base is added while controlling pH with pH-meter. (This is a monster-phrase, but I am too tired after 30 miles on bike to think in English :) ).
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Offline lemonoman

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Re:pH calculation lectures - comments welcomed
« Reply #3 on: June 25, 2005, 03:53:36 PM »
(I'm assuming you designed this page yourself):

Man, that stuff looks 'ill' as all da ganstaz say - that means awesome.

I've always thought that the Internet needed an 'authority' on analytical chemistry - a subject that REALLY seems to throw people off balance.  I knew that to be used and popular, it had to be in layman's terms, so that maybe even highschool students could understand - and it had to be easy to use, and appealing to look at.

This site does all three.

That's awesome man, keep it up.

Offline Borek

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Re:pH calculation lectures - comments welcomed
« Reply #4 on: June 25, 2005, 06:05:47 PM »
(I'm assuming you designed this page yourself):

I did.

Quote
Man, that stuff looks 'ill' as all da ganstaz say - that means awesome.

You are welcome :)
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Offline jdurg

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Re:pH calculation lectures - comments welcomed
« Reply #5 on: June 27, 2005, 03:22:39 PM »
Idea of adding H+ concentrations seems wrong to me, but that's only intuition. No idea how to do the calculations, never heard of such programs (but then I have spent last 20 years farfrom chemistry). Whenever I see information about experiments done in mixed solvents pH is measured, not calculated, and to obtain correct pH acid or base is added while controlling pH with pH-meter. (This is a monster-phrase, but I am too tired after 30 miles on bike to think in English :) ).

If you have two Ka's, wouldn't it be just like if you had a diprotic acid?  Couldn't you calculate the overall pH based upon the two different Ka's you have?
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Offline Borek

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Re:pH calculation lectures - comments welcomed
« Reply #6 on: June 27, 2005, 05:55:20 PM »
If you have two Ka's, wouldn't it be just like if you had a diprotic acid?  Couldn't you calculate the overall pH based upon the two different Ka's you have?

No idea what two Ka's you are talking about :(

As I see it Ka is a function of solution composition, with highest value for 100% H2O and lowest for 0% H2O. Perhaps dependence is linear - I doubt, but then it may be so close to linear that it doesn't matter. Knowing Ka as a function of - say - water molar fraction, one may try to do the classic calculations of pH for weak acid. As we don't know the dependence between Ka and solution composition whole idea is academic.

But Ka is only part of the problem. What happens with activities in the solution containing other than water, less polar solvent? Activities are partially dependent on electrostatic interactions between ions, these will depend on dielectric constant which changes with the solution composition. No idea what will be the outcome.
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