Question

Thisosulphate reacts differently with iodine and bromine in the reactions given below:

$2S_{2}O_{3}^{2 -} + I_{2} \rightarrow S_{4}O_{6}^{2 -} + 2I^{-}$

$S_{2}O_{3}^{2 -} + 2Br_{2} + 5H_{2}O \rightarrow 2SO_{4}^{2 -} + 2Br^{-} + 10H^{+}$

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. Thisoulphate 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)

Bromine is a stronger oxidant than iodine.

Answer 2

: $Br_{2}$oxidizes S to a higher oxidation state

(i.e.; ) and $I_{2}$oxidizes S to a lower oxidation state (i.e; $\overset{+ 2}{S_{2}}O_{3}^{2 -} \rightarrow \overset{+ 2.5}{S_{4}}O_{6}^{2 -}$). Thus, $Br_{2}$ is stronger oxidizing agent than $I_{2}$