Thiosulphate reacts differently with iodine and bromine in the reactions given below: 2 S _2 O ^ 2- _3 + I S _4 O ^ 2- _6 + 2 I ^ - S _2 O ^ 2- _3 + 2 Br _2 + 5 H _2 O 2 SO ^ 2- _4 + 2 Br ^ - + 10 H ^ + Which of the following statements justifies the above dual behaviour of thiosulphate?

Thiosulphate reacts differently with iodine and bromine in the re…

MCQ

Thiosulphate reacts differently with iodine and bromine in the reactions given below: $\ce{2 {S}_2{O}^{2-}_3 + {I}\xrightarrow{ \ \ \ \ \ \ \ } {S}_4{O}^{2-}_6 + 2 {I}^{-}{S}_2{O}^{2-}_3 + 2{Br}_2 + 5 {H}_2{O}\xrightarrow{ \ \ \ \ \ \ \ }2{SO}^{2-}_4 + 2 {Br}^{-} + 10 {H}^{+}}$ Which of the following statements justifies the above dual behaviour of thiosulphate?

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

✓

Answer

Correct option: A.

Bromine is a stronger oxidant than iodine.

$\ce{2{S}_2{O}^{2-}_3({aq}) + {I}_2 {(s)}\xrightarrow{ \ \ \ \ \ \ \ \ \ } {S}_4{O}^{2-}_6({aq}) + 2{I}^{-}({aq})$
${S}_2{O}^{2-}_3({aq}) + 2{Br}({l}) + 5{H}_2 {O}({l})\xrightarrow{ \ \ \ \ \ \ \ \ \ }2{SO}^{2-}_4({Aq}) + 4 {Br}^{-}({aq}) + 10 {H}^{+}({aq})}$
Bromine being stronger oxidizing agent than $I_2$, it oxidises S of $\mathrm{S}_2 \mathrm{O}^{2-}{ }_3$ to $\mathrm{SO}^{2-}{ }_4$ whereas $\mathrm{I}_2$ oxidises it only into $\mathrm{S}_4 \mathrm{O}^{2-}{ }_6$ ion.