12. Solving a chemistry problem

3. The analyzed solution of hydrochloric acid with a volume of 25.0 ml was diluted with distilled water to 100 ml and the test solution was obtained. We took 20.0 ml of the test solution, carried out its potentiometric titration with a standard 0.1000 mol/l sodium hydroxide solution and obtained the following results (Vt, ml are the volumes of added titrant):
Tue 18.00 19.00 19.90 20.00 20.10 21.00 22.00
pH 2.28 2.59 3.60 7.00 10.60 11.49 11.68
Determine the molar concentration of hydrochloric acid in the analyzed solution.