An unknown mass of Na2O (molar mass =61.979g/mol ) was dissolved in enough water to create a 150.0mL stock solution. A 5.00mL sample of the stock solution was transferred to a volumetric flask and diluted to 500.0mL. The pH of the dilute solution is 13.09. Calculate the concentration of OHions in the dilute solution. concentration: M Calculate the concentration of OHions in the stock solution. concentration: M Determine the original mass of Na2O dissolved in the stock solution. mass of Na2O : g