[jjhixon]

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    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?)

[Borek]

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.