[Seks]

300 ml of 0.2 M of one of the 20 standard amino acids.
Titrate with 1.0M NaOH.
I am given a titration curve.

How do I determine which amino acid got titrated?

.3*0.2 = .06 mol of amino acid

Assuming using .3L of NaOH,

.3*1 = .3 mol of NaOH

I'm not sure where to go from here? 

For some reason I always have trouble with titration problems 

[Borek]

It's a shape of the curve that holds necessary information.

[enahs]

Here are the pKa's for the 20 amino acids and their acidic groups.

http://www.bmrb.wisc.edu/referenc/aapka.html


Also notice and memorize the general pKa's for the Carboxylic group and the amine group.

[Seks]

On the curve,

0.5 OH- added, it's at pH 2
1.5 OH- added, it's at pH 8
2.5 OH- added, it's at pH 10ish

(pH for 1.0, 2.0, 3.0 OH- added are indicated but I dont' think those values are relevant??)

I use that pH = pKa + log [A-]/[HA] equation, where A- = .3 and HA = .06.

But for pH 2 and 8, I get pKa 1.3 and 7.3 respectively. And those values don't jive with any pKa values on my table of amino acids.

I must be missing something? or a step somewhere...

[Yggdrasil]

Exactly between equivalence points of a titration curve, [A-] = [HA].  What does this tell you about the pKa values for the various functional groups on the amino acid?

[edit: thanks for the correction Borek]

[Borek]

At the equivalence point of a titration curve (where pH changes sharply with added OH), [A-] = [HA].

Sounds like one of these "before coffee" answers

What Ygg is trying to point out is that there are points on the curve where pH=pKa without any further corrections.

[Seks]

Well, when 0.5 OH- is added, pKa = pH, so which means that's pKa 2.
1.5 OH-, pKa = 8
so on

But using 1 mol/L of OH- for 0.3L of 0.2 mol/L amino acid, how will those amounts/quantities affect what I'm trying to find?

[Borek]

But using 1 mol/L of OH- for 0.3L of 0.2 mol/L amino acid, how will those amounts/quantities affect what I'm trying to find?

Assuming 0.5 OH^- means just molar ratio of base added to your aminoacid, concentrations don't matter (much, they do a little, but the effect can be neglected). It is their ratio that counts - and ratio is what you use as input.