0.4850 g of limestone is dissolved in acid and all calcium is precipitated as CaC2O4. The precipitate is filtered, dissolved in dilute H2SO4 and the oxalate titrated with 0.0200 M KMnO4, requiring 29.7 mL. Taking CaCO3=100, find the percentage of CaCO3 in the limestone (two decimals).

JEE Advanced levelNumerical answerDifficulty 3 of 3eq199

$0.4850 g$ of limestone is dissolved in acid and all calcium is precipitated as $CaC X_{2} O X_{4}$ . The precipitate is filtered, dissolved in dilute $H X_{2} SO X_{4}$ and the oxalate titrated with $0.0200 M$ $KMnO X_{4}$ , requiring $29.7 mL$ . Taking $CaCO X_{3} = 100$ , find the percentage of $CaCO X_{3}$ in the limestone (two decimals).

Numerical answer type, answer in %, tolerance 0.05.

Mmol of oxalate

= 29.7 \times 0.0200 \times 5/2 = 1.485

, and each oxalate corresponds to one

Ca X^{2 +}

and hence one

CaCO X_{3}

. Mass

= 1.485 \times 100 = 148.5

mg. Percentage

= 148.5/485.0 \times 100 = 30.62%