Question

Thiosulphate reacts differently with iodine and bromine in the reactions given below:
$2S_{2}O^{2-}_{3} + I_{2} \to S_{4}O^{2-}_{6} + 2I^{-}$
$S_{2}O_{3}^{2-} + 2Br_{2} + 5H_{2}O \to 2SO^{2-}_{4} + 2Br^{-} + 10H^{+}$
Which of the following statements justifies the above dual behaviour of thiosulphate?

• A. 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 1

Answer: (A)

$Br_2$ oxidises $S$ to a higher oxidation state and $I_2$ oxidises $S$ to a lower oxidation state . Thus, $Br_2$ is stronger oxidising agent than $I_2$.