Q15 / 90 · JEE Main 2024 (08 Apr Shift 1) · Chemistry

Thiosulphate reacts differently with iodine and bromine in the reactions given below: \(\begin{aligned} & 2 \mathrm{~S}_2 \mathrm{O}_3^{2-}+\mathrm{I}_2 \rightarrow \mathrm{S}_4 \mathrm{O}_6^{2-}+2 \mathrm{I}^{-} \\ & \mathrm{S}_2 \mathrm{O}_3^{2-}+5 \mathrm{Br}_2+5 \mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{SO}_4^{2-}+4 \mathrm{Br}^{-}+10 \mathrm{H}^{+} \end{aligned}\) Which of the following statement justifies the above dual behaviour of thiosulphate?

  • Correct answer
    A
    Bromine is a stronger oxidant than iodine
  • B
    Thiosulphate undergoes oxidation by bromine and reduction by iodine in these reaction
  • C
    Bromine is a weaker oxidant than iodine
  • D
    Bromine undergoes oxidation and iodine undergoes reduction in these reactions

Solution

In the reaction of $\mathrm{S}_2 \mathrm{O}_3{ }^{2-}$ with $\mathrm{I}_2$, oxidation state of sulphur changes to +2 to +2.5 In the reaction of $\mathrm{S}_2 \mathrm{O}_3{ }^{2-}$ with $\mathrm{Br}_2$, oxidation state of sulphur changes from +2 to +6 . $\therefore$ Both $\mathrm{I}_2$ and $\mathrm{Br}_2$ are oxidant (oxidising agent) and $\mathrm{Br}_2$ is stronger oxidant than $\mathrm{I}_2$.

Hence, the correct answer is option: 'A'.

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