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Standard XII

Chemistry

Types of Solution

1.6 g of pyro...

Question

$1.6 g$ of pyrolusite ore was treated with $50 c m^{3}$ of $1.0 N$ oxalic acid and some sulphuric acid. The oxalic acid left undecomposed was raised to $250 c m^{3}$ in a flask. $25 c m^{3}$ of this solution when titrated with $0.1 N K M n O_{4}$ required $32 c m^{3}$ of the solution. Find the percentage of pure $M n O_{2}$ in the sample and also the percentage of available oxygen.

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Solution

$25 c m^{3}$ of undecomposed oxalic acid required
$= 32 c m^{3} 0.1 N K M n O_{4}$ solution
Thus, $250 c m^{3}$ of undecomposed oxalic acid required
$= 320 c m^{3} 0.1 N K M n O_{4}$ solution
$\equiv 32 c m^{3} 1 N K M n O_{4}$ solution
$= 32 c m^{3} 1 N$ oxalic acid solution
Oxalic acid used by pyrolusite
$= (50 - 32) c m^{3} 1 N$ solution
$= 18 c m^{3} 1 N$ solution
$\equiv 18 c m^{3} 1 N M n O_{2}$ solution
Mass of $M n O_{2} = \frac{N \times E \times V}{1000} = \frac{1 \times 18 \times 87}{1000 \times 2} = 0.783 g$
Percentage of $M n O_{2} = \frac{0.783}{1.6} \times 100 = 48.9$
$M n O_{2} 87 g \to M n O + O 16 g$
Oxygen given by $0.783 g M n O_{2} = \frac{16}{87} \times 0.783 = 0.144 g$
% of available oxygen $= \frac{0.144}{1.6} \times 100 = 9.0$ .

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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

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0.01 N

K M n O_{4}

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mL of the solution. The percentage of pure

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3.2 g

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

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Given: Atomic mass of

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3.2 g

of pyrolusite

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0.5 M

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

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1.6 g

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Q. A

1.5

g sample containing oxalic acid and some inert impurity was dissolved in enough water and volume was made up to

250

mL. A

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30

mL of an alkali solution. The resulting solution was then treated with stoichiometric amount of

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just needed for precipitation of oxalate as

C a C_{2} O_{4}

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8.0

mL of acid was required to reach the equivalence point. At last the above neutral solution was treated with excess of

A g N O_{3}

solution and

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g. Determine the mass percentage of oxalic acid in the original sample.

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