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Topic: How do you determine pKa of an acid if you have...?  (Read 14573 times)

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Offline o1ocups

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How do you determine pKa of an acid if you have...?
« on: March 10, 2009, 03:53:03 PM »
A 0.446 g sample of an unknown monoprotic acid was titrated with 0.105 M KOH and the resulting titration curve is shown in the figure (Intro 1 figure)  Determine pka of the acid.

Using the information from the figure, I have already determined the molar mass of the unknown acid. For this question I know I have to use pH = pka + log([base]/[acid]) but I don't know how to get [base]/[acid] at the equivalence point. According to the figure the pH is about 8 at the equivalence point.

Any help would be greatly appreciated!!
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Offline sjb

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Re: How do you determine pKa of an acid if you have...?
« Reply #1 on: March 10, 2009, 04:28:33 PM »
What does equivalence mean, in this context?

S
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Offline Borek

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Re: How do you determine pKa of an acid if you have...?
« Reply #2 on: March 10, 2009, 05:04:32 PM »
There is a special point on the titration curve of a weak acid where pKa = pH.
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Offline o1ocups

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Re: How do you determine pKa of an acid if you have...?
« Reply #3 on: March 10, 2009, 05:29:09 PM »
I got it now. Thanks.
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