The balanced reaction would be as follows:
3NaOH + H3PO4 --> Na3PO4 + 3H20
We are given the concentration and the amount of the reactants to be used. We use these values for the calculations as follows:
How many mL of .225 M NaOH will react with 4.568g H3PO4?
4.568 g (1 mol / 98 g) ( 3 mol NaOH / 1 mol H3PO4 ) ( 1 L / .225 mol NaOH ) = 0.621 L or 621 mL of .225 NaOH