Use Mn = 55, Na = 23, C = 12, O = 16. A 0.500 g sample of pyrolusite (impure MnO2) is heated with 0.670 g of Na2C2O4 and excess dilute H2SO4 (MnO2 reduced to Mn^2+, oxalate oxidised to CO2). The unreacted oxalate needs 18.4 mL of 0.0200 M KMnO4 (to Mn^2+). Find the mass percentage of MnO2 in the sample (two decimals).

JEE Advanced levelNumerical answerDifficulty 3 of 3rx153

Use Mn = 55, Na = 23, C = 12, O = 16. A $0.500 g$ sample of pyrolusite (impure $MnO X_{2}$ ) is heated with $0.670 g$ of $Na X_{2} C X_{2} O X_{4}$ and excess dilute $H X_{2} SO X_{4}$ ( $MnO X_{2}$ reduced to $Mn X^{2 +}$ , oxalate oxidised to $CO X_{2}$ ). The unreacted oxalate needs $18.4 mL$ of $0.0200 M$ $KMnO X_{4}$ (to $Mn X^{2 +}$ ). Find the mass percentage of $MnO X_{2}$ in the sample (two decimals).

Numerical answer type, answer in %, tolerance 0.05.

Oxalate added

= 0.670/134 = 5.00

mmol. Excess oxalate

= 18.4 \times 0.0200 \times (5/2) = 0.92

mmol. Oxalate used

= 4.08

mmol.

MnO X_{2}

(

n = 2

) and oxalate (

n = 2

) react 1:1, so

MnO X_{2} = 4.08

mmol

= 0.3550 g

. Percentage

= 70.99%