[MuskieMan33]

I did a lab recently, using 3 acids of unknown concentration (HCl, acetic, and maleic, all 3 titrated with 0.260 M NaOH), a pH meter, and making a titration curve from the data. Finding the concentration of the HCl, I understand how to do [antilog(-initial pH)]. But when it comes to calculating the Ka of HCl, I get lost when determining what numbers go in which part of the equation. I know that Ka=[H+][A-]/[HA]. This stumped me on my test recently as well.
When it comes to the maleic acid and acetic acid, I don't even know where to begin. I'm not looking for someone to do my calculations for me, just an explanation of how to approach it so I can finally learn this and lay it to rest. I do have the titration curves for all 3 solutions. I know where the equivalence and half equivalence points are as well on the HCl and acetic acids, but another question I had was when it come to the diprotic maleic acid, do I use the first or second equivalence point? The steeper of the two? I would appreciate any input anyone has in helping me come closer to solving this chemistry hump I've hit!

[enahs]

http://www.chem.ufl.edu/~itl/2045/lectures/lec_z2.html

[MuskieMan33]

It seems that that article had the acids concentration, as that is what I'm trying to determine. Can I just use antilog(-pH) for a weak acid as well? I didn't think I could, I was under the impression that I had to use the half equivalence point and equivalence point in some way to determine the concentration? Sorry for being a pain. Also, on calculation B, is it necessary for me to know the number of moles of OH- in determining the concentration of a weak acid? Thanks for posting that article, I'm going to re-read it and hopefully pick up some more to make better sense of everything.