124. Solving a chemistry problem

3. Potentiometric titration of 20 ml of acetic acid solution with a standard solution of sodium hydroxide with a concentration of 0.100 mol/l was carried out and the following results were obtained (Vt, ml is the volume of added titrant):
Vt, ml 18.00 19.00 19.50 19.90 20.00 20.10 20.50 21.00
pH 5.71 6.04 6.35 7.05 8.79 10.52 11.22 11.51
Find the molar concentration and mass of acetic acid in the analyzed solution from the differential potentiometric titration curve.