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Topic: Buffer solution  (Read 3257 times)

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Offline ham123

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Buffer solution
« on: April 23, 2012, 09:10:50 AM »
A solution of pH 3.8 is to be made by mixing 1 M solution of ethanoic acid (pKa=4.74) and sodium ethanoate. What proportion by volume should two solutions be mixed?
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Offline ham123

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Re: Buffer solution
« Reply #1 on: April 23, 2012, 09:23:15 AM »
http://answers.yahoo.com/question/index?qid=20110821143137AAg5ThX

I saw the question over here. however, I don't really understand how to use the Henderson hassalbalch equation. I hope somebody could explain that to be without using the equation.

pH = pKa + log (moles base/ moles acid)
3.80 = 4.74 + log (base/acid)
-0.94 = log (base/acid)
10^-0.94 = (base/acid)
0.115 = (base/acid)

ratio of moles of base to acid = 0.115:1.
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Offline AWK

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Re: Buffer solution
« Reply #2 on: April 23, 2012, 09:29:00 AM »
Convert pH to H3O+ concentration and use dissociation expression for acetic acid instead.
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Offline Borek

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Re: Buffer solution
« Reply #3 on: April 23, 2012, 10:20:36 AM »
Hendrson-Hasselbalch equation is just a rearranged dissociation constant, so it doesn't matter which one you use.
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