Some Basic Concepts of Chemistry - Result Question 24
24. For the reaction, $I^{-}+ClO _3^{-}+H _2 SO _4 \longrightarrow Cl^{-}+HSO _4^{-}+I _2$ the correct statement(s) in the balanced equation is/are
(2014 Adv)
(a) stoichiometric coefficient of $HSO _4^{-}$is 6
(b) iodide is oxidised
(c) sulphur is reduced
(d) $H _2 O$ is one of the products
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Answer:
Correct Answer: 24. (a, b, d)
Solution:
PLAN This problem includes concept of redox reaction. A redox reaction consists of oxidation half-cell reaction and reduction half-cell reaction. Write both half-cell reactions, i.e. oxidation half-cell reaction and reduction half-cell reaction.Then balance both the equations.
Now determine the correct value of stoichiometry of $\mathrm{H}_2 \mathrm{SO}_4$. Oxidation half-reaction, $2 \mathrm{I}^{-} \longrightarrow \mathrm{I}_2+2 e^{-}………..(i) $
Here, $\mathrm{I}^{-}$is converted into $\mathrm{I}_2$. Oxidation number of I is increasing from -1 to 0 hence, this is a type of oxidation reaction.
Reduction half-reaction
$6 \mathrm{H}^{+}+\mathrm{ClO}_3^{-}+6 e^{-} \longrightarrow \mathrm{Cl}^{-}+3 \mathrm{H}_2 \mathrm{O}………..(ii) $
- Here, $\mathrm{H}_2 \mathrm{O}$ releases as a product. Hence, option (d) is correct. Multiplying equation (i) by 3 and adding in equation (ii)
$\begin{aligned} 6 \mathrm{I}^{-}+\mathrm{ClO}_3^{-}+6 \mathrm{H}^{+} \longrightarrow \mathrm{Cl}^{-}+3 \mathrm{I}_2+3 \mathrm{H}_2 \mathrm{O} \\ 6 \mathrm{I}^{-}+\mathrm{ClO}_3^{-}+6 \mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{Cl}^{-}+3 \mathrm{I}_2+3 \mathrm{H}_2 \mathrm{O}+6 \mathrm{HSO}_4^{-} \end{aligned}$
- Stoichiometric coefficient of $\mathrm{HSO}_4^{-}$is 6 . Hence, option (a), (b) and (d) are correct.
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