A sample of 0.1276 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.0633 M NaOH solution. The volume of base required to reach the equivalence point was 18.4 mL. (a) Calculate the molar mass of the acid, (b) After 10.0 mL of base had been added to the titration, the pH was deter- mined to be 5.87. What is the K_a of the unknown acid?