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Stoichiometric Calculations

Ozone is esti...

Question

Ozone is estimated in air by passing certain volume of air through an acidified or neutral or basic $K I$ solution when $O_{2}$ is evolved and $I^{⊝}$ is oxidised to $I_{2}$ . Free $I_{2}$ evolved is titrated with standard $N a_{2} S_{2} O_{3}$ solution. In an experiment, $10$ L of air at $1$ atm and $27^{o} C$ was passed through an alkaline $K I$ solution and $I_{2}$ liberated required $2$ mL of $\frac{M}{800}$ $N a_{2} S_{2} O_{3}$ solution. The volume percentage of $O_{3}$ in sample is :

2.463 \times 10^{- 3} %

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2.563 \times 10^{- 3} %

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2.473 \times 10^{- 3} %

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none of the above

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Solution

The correct option is B $2.463 \times 10^{- 3} %$
The balanced redox reactions in basic medium are as follows:
$2 I^{⊝} + H_{2} O + O_{3} \to O_{2} + I_{2} + 2 ⊝ O H$ $(n$ factor $O_{3} = 2)$
$I_{2} + 2 e^{-} \to 2 I^{⊝} (n = 2)$
$S_{2} O_{3}^{2 -} + 10 ⊝ O H \to 2 S O_{4}^{2 -} + 5 H_{2} O + 8 e^{-} (n = 8)$
$∴ m E q$ of $I_{2} = m E q$ of $N a_{2} S_{2} O_{3}$
$∴ 2 \times \frac{1}{800} \times 8$ $(n$ factor $)$ $= 0.02$
$m m o l e s$ of $I_{2} = \frac{0.02}{2} =$ $m m o l e s$ of $O_{3}$
$[∵ n = 2$ , for both or, Molar ratio of $O_{3} : I_{2} :: 1 : 1]$
$P_{O_{3}} = \frac{n R T}{V}$
$= \frac{0.01 \times 10^{- 3} \times 0.0821 \times 300}{10}$ $= 246.3 \times 10^{- 7} a t m$
Volume % of $O_{3} = 246.3 \times 10^{- 7} a t m$ $= 2.463 \times 10^{- 3}$ %

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Similar questions

Q. For estimating ozone in the air, a certain volume of air is passed through an acidified potassium iodide solution. Oxygen is evolved and iodide is then oxidized to give iodine. When such a solution is acidified, free iodine is evolved which can be titrated with standard sodium thio-sulphate solution. In an experiment

10 l i t r e

of air at

1

atm and

27^{o} C

were passed through an alkaline

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solution, at the end, the iodine entrapped in the solution on titration as above required

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0.01 N N a_{2} S_{2} O_{3}

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Q. In an experiment,

10

L of air (containing

O_{3}

) at

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solution. The molar percentage of

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solution was electrolyzed using inert electrodes by passing current till the

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638.0

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