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Topic: calculating the pH after titrating?  (Read 1929 times)

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Offline SOS

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calculating the pH after titrating?
« on: June 11, 2011, 09:55:52 PM »
http://answers.yahoo.com/question/index?qid=20100326105220AAweUVk&pa=FZB6NXXtFWMW0cLWwOod.OFv5Q0dJ1pTr7OXJIZ47CcpqI8pDJU-&paid=add_watch

is Dr. A wrong here? Isn't according to the H-H equation it is the pH= pKa + log([H]/[HA])? He's using moles not the concentrations of [H] and [HA].

EDIT: Also, can you always use the H-H equation when your have weak acid/base leftover after the titrating? is it always reliable?
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Offline Borek

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Re: calculating the pH after titrating?
« Reply #1 on: June 12, 2011, 06:09:57 AM »
Ratio of concentrations is identical to ratio of number of moles - volume cancels out.

See Henderson-Hasselbalch equation for the discussion of the HH equation applicability.
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Offline lillybeans

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Re: calculating the pH after titrating?
« Reply #2 on: June 16, 2011, 05:53:34 PM »
Well, I never use the formula, I always do it the long way but I arrived at the same answer as Dr.A I got pH = 4.5, close enough. So he should be right.

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