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Equivalent Mass

3.2 g of pyro...

Question

$3.2 g$ of pyrolusite $(M n O_{2})$ was treated with $50 m L$ of $0.5 M$ oxalic acid and some sulphuric acid. The oxalic acid left undecomposed was raised to $250 m L$ in a flask. $25 m L$ of this solution when treated with $0.02 M K M n O_{4}$ required $32 m L$ of the solution. Find the percentage of $M n O_{2}$ in the sample.
Given: Atomic mass of $M n$ is $55 g m o l^{- 1}$

A

4.5 %

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B

24.4 %

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C

54.0 %

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D

11.5 %

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Solution

The correct option is B $24.4 %$
$n-factor = | Change in O.S. | \times Number of atoms$

Redox changes are
${+ 3 C}_{2} O_{4}^{2 -} \to 2 + 4 C O_{2}$ (n-factor = 2)
$+ 7 M n O_{4}^{-} \to + 2 M n^{2 +}$ (n-factor = 5)
$+ 4 M n O_{2} \to + 2 M n^{2 +}$ (n-factor = 2)

$Milliequivalents of oxalic acid left (in 25 m L) = Milliequivalents of K M n O_{4} = 32 \times 0.02 \times 5 = 3.2$
$Milliequivalents of oxalic acid left (in 250 m L) = 3.2 \times \frac{250}{25} = 32$

$Milliequivalents of oxalic acid taken = 50 \times 0.5 \times 2 = 50$
$Milliequivalents of M n O_{2} = Milliequivalents of (oxalic acid taken - oxalic acid left (in 250 m L))$
$∴ Milliequivalents of M n O_{2} = 50 - 32 = 18$
$\frac{W_{M n O_{2}}}{M_{M n O_{2}}} \times 2 \times 1000 = 18$
$\Rightarrow \frac{W_{M n O_{2}}}{55 + 2 (16)} \times 2 \times 1000 = 18$
$∴ W_{M n O_{2}} = 0.783 g$
$∴ % o f M n O_{2} = \frac{0.783}{3.2} \times 100 = 24.4 %$

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Similar questions

3.2 g

(M n O_{2})

was treated with

50 m L

0.5 M

oxalic acid and some sulphuric acid. The oxalic acid left undecomposed was raised to

250 m L

25 m L

of this solution when treated with

0.02 M K M n O_{4}

32 m L

of the solution. Find the percentage of

M n O_{2}

in the sample.
Given: Atomic mass of

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55 g m o l^{- 1}

3.2 g

(M n O_{2})

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oxalic acid and some sulphuric acid. The oxalic acid left undecomposed was raised to

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of this solution when treated with

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Given: Atomic mass of

M n

55 g m o l^{- 1}

1.6

g of pyrolusite ore was treated with

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oxalic acid and some sulphuric acid. The oxalic acid left in excess was raised to

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Equivalent Mass

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