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Topic: Amino Acid Titration with weak Base  (Read 2569 times)

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Offline jjhixon

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Amino Acid Titration with weak Base
« on: September 21, 2009, 12:10:39 AM »
Question is as follows..

50 ml of 1.0 M cysteine solution, initially at pH 0 (completely protonated) is titrated with 0.1 M of NaOH to final pH of 13. pKa values of Cysteine are 2.3, 8.3 and 9.6.

What are the values of NaOH need to reach the pKa values?

What i tried

- Basically i need to know how to begin the question.

i've tried balancing the equation and assigning the mmoles

5cys + 1NaOH   :rarrow: 5cys + h20

(0.050) x (0.1)= 5 mmoles of cys
1 mmole of NaOH

after this I'm completely lost, anyone have any suggestions (if im even doing the above steps incorrectly?)
« Last Edit: September 21, 2009, 12:23:22 AM by jjhixon »

Offline Borek

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Re: Amino Acid Titration with weak Base
« Reply #1 on: September 21, 2009, 03:05:48 AM »
What do you know about concentrations of acid and conjugate base at pH=pKa?

BTW, if your prof will tell you correct volume to reach pH 2.3 is 250 mL, look for a better teacher. First volume is around 700 mL. And this is no joke - this is a serious error that I have already seen made by narrowly thinking teachers.
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