A solution contains oxalic acid, H₂C₂O₄, and sodium hydrogen oxalate, NaHC₂O₄. A 25.0 mL portion needs 20.0 mL of 0.100 mol L⁻¹ NaOH to reach the phenolphthalein end point. A second 25.0 mL portion, in acid, needs 16.0 mL of 0.0400 mol L⁻¹ KMnO₄, where 2 MnO₄⁻ + 5 C₂O₄²⁻ + 16 H⁺ → 2 Mn²⁺ + 10 CO₂ + 8 H₂O. What is the molarity of NaHC₂O₄ in the solution? | StemPy Lab