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Standard XII

Chemistry

Osmotic Pressure

1.6 g of pyro...

Question

$1.6$ g of pyrolusite ore was treated with $50$ mL of $0.1 N$ oxalic acid and some sulphuric acid. The oxalic acid left in excess was raised to $250$ mL in a flask. $25$ mL of this solution when titrated with $0.01 N$ $K M n O_{4}$ required $30$ mL of the solution. The percentage of pure $M n O_{2}$ in the sample is :

10.86 %

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5.43 %

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1.086 %

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none of the above

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Solution

The correct option is B $5.43 %$
$M n O_{2} (1.6 g) + H_{2} C_{2} O_{4} 50 m L / 0.1 N ↓ e x c e s s 25 m L \equiv 0.01 N / 30 m L o f K M n O_{4} \to M n^{2 +}$
mEq of $K M n O_{4} \equiv$ mEq of $H_{2} C_{2} O_{4}]_{e x c e s s i n 25 m L}$
$\Rightarrow$ Excess mEq of $H_{2} C_{2} O_{4}$ in $25 m L$
$= 0.01 \times 30 = 0.30$
Excess mEq of $H_{2} C_{2} O_{4}$ in $250 m L = 3.0$
mEq of $H_{2} C_{2} O_{4}$ used $= 5 - 3 = 2$
mEq of $M n O_{2} = 2$
$\frac{W e i g h t}{87 / 2} \times 1000 = 2 \Rightarrow W e i g h t = 0.087 g$
$%$ $M n O_{2} = \frac{0.087}{1.6} \times 100 = 5.43 %$

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1.6 g of pyrolusite ore was treated with 50 mL of 0.1 N oxalic acid and some sulphuric acid. The oxalic acid left in excess was raised to 250 mL in a flask. 25 mL of this solution when titrated with 0.01 N KMnO4 required 30 mL of the solution. The percentage of pure MnO2 in the sample is :