An unknown mass of Na2O (molar mass=61.979 g/mol) was dissolved in enough water to create a 100.0 mL stock solution. A 5.00 mL sample of the stock solution was transferred to a volumetric flask and diluted to 500.0 mL . The pH of the dilute solution is 13.05. Calculate the concentration of OH− ions in the dilute solution. Calculate the concentration of OH− ions in the stock solution. Determine the original mass of Na2O dissolved in the stock solution.