Consider 2.50 L of a buffer solution made from NaOH and 3.50 M H3PO4 at pH 2.16 that has a total concentration of phosphate containing species of 0.151 M. What volume of 3.50 M H3PO4 was required to make the buffer solution? What mass of NaOH was required to make the buffer solution? How many mL of 2.00 M HCl must be added to the buffer solution to change its pH by 1.25 units?