Calculating Concentration of Acid using a pH Titration Curve

[Justinboln]

Homework Statement

calculate the concentration of the acid, HA.

Relevant Equations

not too sure

Use the equivalence volume from the pH curve to calculate the concentration of the acid, HA.
I'm not sure which equation to use or how to approach this question (Attached).
Please elaborate on the steps on how to answer the question.

Thank you!

 

[Borek]

Hint: this is a simple stoichiometry (combined with n=CV). Titration curve is just a way of finding out when the amount of added titrant was equivalent to the amount of the acid present.