A 0.518 g sample of limestone is dissolved in HCl and then the calcium is precipitated as CaC2O4. After filtering and washing the precipitate, it requires 40.0 mL of 0.250 N KMnO4 solution acidified with H2SO4 to titrate it as. The percentage of CaO in the sample isMnO4- + H+ + C2O4-2 →  Mn2+ +CO2 + 2H2O