A 0.5123g sample (molar mass 204.23g/mol) of KHP was dissolved in about 25 mL of distilled water and titrated to the phenolphthalein end point with 28.75 mL of a sodium hydroxide solution. Calculate the molar concentration of the hydroxide solution.
Useful info: Ka2 of KHP = 3.90x10^-6 and pKa2 = 5.408