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7. Redox reactions — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistry7. Redox reactions1 Mark
MCQ
Thiosulphate reacts differently with iodine and bromine in the reaction given below :

$ 2 \mathrm{~S}_2 \mathrm{O}_3^{2-}+\mathrm{I}_2 \rightarrow \mathrm{S}_4 \mathrm{O}_6^{2-}+2 \mathrm{I}^{-}$

$\mathrm{S}_2 \mathrm{O}_3^{2-}+5 \mathrm{Br}_2+5 \mathrm{H}_2 \mathrm{O} \rightarrow 2 \mathrm{SO}_4^{2-}+4 \mathrm{Br}^{-}+10 \mathrm{H}^{+}$

Which of the following statement justifies the above dual behaviour of thiosulphate?

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

Answer

Correct option: C.
Bromine is a stronger oxidant than iodine
c
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 $\mathrm{I}_2$.

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