[sarah9625]

I need to determine the molecular weight of a weak acid from titration data?
I nkow that I use the ml of NaOH added at the titration curve x M of NaOH=mmol of OH. Then I take mass of my sample / mmol of OH. But how do I find the mmol of NaOH?
   0.220 g acid     =  molar mass
   4x10-4mole acid

Also, how do I determine the Ka values for this titration? I know that I am to use the equation of Ka=(H3O)(A)/(HA) iknow :
Ka = [H3O+][A]
                [HA]

For example I titrated an unknown soild that was mixed with 100 ml of distilled water with NaOH until it became basic. I made a titration curve on a graph. Is there a way to find out the the molecular weight of the weak acid?
Heres my data:
pH          NaOH added(ml)
2.8          0
3.3          1
4          2
5.1          3
6          4
7          4
8          4
9*Eqv.pt          4*
10          4
11.2          4
11.6          5
11.8          6
12          7
12.1          8
12.2          9
12.2          10