Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: jjhixon 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?)
-
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.