I am given that volume of an unknown acid is 25 mL, volume of NaOH is 13 mL and concentration of NaOH is 1.0 M. I have a graph of a titration curve where the equivalence point is pH=9 (pH on y axis and volume of NaOH on x axis)
How would i find the pKa value as well as the Ka value?
Read the volume on the graph at the equivalence point, take half that volume, look on the graph and find the pH at that 1/2 volume point, that will give you the pH at the half way point and that will be pKa. Convert to Ka.
What you are doing is using the Henderson-Hasselbalch equation of
pH = pKa + log (base)/(acid)
When the acid/base titration curve is at the exact half way point to the equivalence point then exactly half of the acid or base has been neutralized and exactly half of the acid or base remains un-neutralized. So (base) = (acid) and base/acid in the HH equation is 1, log 1 is zero, and pH = pKa. Neat, eh?