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  4. 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 is: MnO-4 + H+ + C2O42 → Mn2+ + CO2 + 2H2O

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Q. A 0.518 g sample of limestone is dissolved in HCl and then the calcium is precipitated as $CaC_{2}O_{4}$. After filtering and washing the precipitate, it requires $40.0$ mL of $0.250 N KMnO_{4}$ solution acidified with $H_{2}SO_{4}$ to titrate it as. The percentage of CaO in the sample is:
$MnO^{-}_{4} + H^{+} + C_{2}O_{4}^{2} \to Mn^{2+} + CO_{2} + 2H_{2}O$

Redox Reactions

Solution:

M eq. of $KMnO_{4} =$ M eq. of $C_{2}O_{4}^{2-} =$ M eq. of $CaCO_{3}$
$40 \times .25 =$ Meq of $CaO$
$\frac{10 \times10^{-3}}{2} =$ mol of $Cao$
$\% Cao =\frac{5\times10^{-3} \times56\times100}{.518}$
$Cao =54 \%$