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Byju's Answer

Standard X

Chemistry

Oxidation and Reduction

As2O3 is inso...

Question

$A s_{2} O_{3}$ is insoluble in water but soluble in 10% NaOH solution. The solution of $A s_{2} O_{3}$ in NaOH is titrated against iodine (in presence of $N a H C O_{3}$ which does not react with iodine, but neutralises the $H I$ formed). The two steps are represented as:

$A s_{2} O_{3} + 6 N a O H \to 2 N a_{3} A s O_{3} + 3 H_{2} O$
$2 N a_{3} A s O_{3} + 2 I_{2} + 2 H_{3} O \to 2 N a_{3} A s O_{4} + 4 H I$

The equivalent weight of $A s_{2} O_{3}$ is (At. wt. of $A s = 75$ ):

198

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49.5

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Solution

The correct option is D 49.5
The molecular weight of $A s_{2} O_{3}$ is $2 (75) + 3 (16) = 198 g / m o l$ .
The oxidation number of As changes from $+ 3$ to $+ 5$ .
The change in the oxidation number per As atom is $+ 2$ .
Total change in the oxidation number for 2 As atoms is $+ 4$ .
The equivalent weight of $A s_{2} O_{3}$ is $\frac{Molecular weight}{change in the oxidation number} = \frac{198}{4} = 49.5$ .

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Similar questions

Q. A mixture containing

A s_{2} O_{3}

and

A s_{2} O_{5}

required

20.10

mL of

0.05 N

iodine for titration. The resulting solution is then acidified and excess of

K I

was added. The liberated iodine required

1.1113

g hypo

(N a_{2} S_{2} O_{3} .5 H_{2} O)

for complete reaction. Calculate the mass of mixture. The reactions are as follows:

A s_{2} O_{3} + 2 I_{2} + 2 H_{2} O ⟶ A s_{2} O_{5} + 4 H^{+} + 4 I^{-}

A s_{2} O_{5} + 4 H^{+} + 4 I^{-} ⟶ A s_{2} O_{3} + 2 I_{2} + 2 H_{2} O

Q. A

0.1097 g

sample of

A s_{2} O_{3}

required

36.10 m L

K M n O_{4}

solution for its titration. The molarity of

K M n O_{4}

solution is (Given Molecular mass of

A s_{2} O_{3} = 198

)

Q. An impure sample of

A s_{2} O_{3}

weighing

20 g m

was dissolved in water containing

10 g m o f N a H C O_{3}

and the final solution was diluted to

400 m L

20 m L

of this solution was oxidised by

25 m L

of a solution of

I_{2}

. Another solution of hypo containing

1.24 g m

N a_{2} S_{2} O_{3} .5 H_{2} O

40 m L

was used to exactly reduce

25 m L

of same

I_{2}

solution (impurities inert) calculate % of

A s_{2} O_{3}

in the sample (at. wt. of As = 75)

Q. A

0.1097 g

sample of

A s_{2} O_{3}

required

36.10 m L

K M n O_{4}

solution for its titration. The molarity of

K M n O_{4}

solution is (Given Molecular mass of

A s_{2} O_{3} = 198

)

Q. The solubility product of

A s_{2} O_{3}

10.8 \times 10^{- 9}

. It is 50% dissociated in a saturated solution. The solubility of salt is:

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