Thiosulphate reacts differently with iodine and bromine in the reactions given below. $2 \mathrm{~S}_{2}…

Thiosulphate reacts differently with iodine and bromine in the reactions given below.
$2 \mathrm{~S}_{2} \mathrm{O}_{3}^{2-}+\mathrm{I}_{2} ightarrow \mathrm{S}_{4} \mathrm{O}_{6}^{2-}+2 \mathrm{I}^{-}$
$\mathrm{S}_{2} \mathrm{O}_{3}^{2-}+2 \mathrm{Br}_{2}+5 \mathrm{H}_{2} \mathrm{O} ightarrow 2 \mathrm{SO}_{4}^{2-}+2 \mathrm{Br}^{-}+10 \mathrm{H}^{+}$
Which of the following statements justifies the above dual behaviour of this sulphate?
  1. Bromine is a stronger oxidant than iodine
  2. Bromine is a weaker oxidant than iodine
  3. Thiosulphate undergoes oxidation by bromine and reduction by iodine in these reactions
  4. 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 \(B r_2\) is stronger oxidant then \(I_2\).

Asked in: JEE-TOPICTESTS-CHEMISTRY

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