When a 15.0 mL sample of 5.45 g/L solution of a diprotic acid was titrated against 0.15 M KOH, it required 24.50 mL of the base to reach the endpoint. The pH values at the first and second equivalence points were 5.75 and 10.75, respectively. Calculate the pKa1, pKa2, and the molecular weight of the acid.