Since the diprotic acid is unknown, let's represent this as: H₂X. So, the reaction would proceed as:
H₂X + 2 NaOH --> Na₂X + 2 H₂O
The solution is as follows:
0.2 mol/L NaOH * 30 mL * 1 L/1000 mL * 1 mol H₂X/2 mol NaOH = 0.003 mol H₂X
Concentration = 0.003 mol H₂X/25 mL * 1000 mL/1 L = 0.12 M H₂X
