Question

Question 8.14 Consider the reactions:

2S2O3(2-) (aq) + I2(s)→ S4O6(2-)(aq) + 2I–(aq)

S2O3(2-) (aq) + 2Br2(l) + 5 H2O(l)→2SO4(2-)(aq) + 4Br–(aq) + 10H+(aq)

Why does the same reductant, thiosulphate react differently with iodine and bromine?

Class XI Redox Reactions Page 273

Answer 1

Hi

Please see the attached file!

Hope it helps you !

Answer 2

Bromine is stronger oxidizing agent than iodine. it oxidises S of S2O3 to a higher oxidation state +6 in SO4^2- . while I2 oxidises S of S2O3 to a lower oxidation state 2.5 in S4O6^2-. for better understanding see reactions.
$2S_2O_3(aq)+I_2--->S_4O_6^{2-}(aq)+2I^-(aq)$
oxidation number of S in S4O6^2- is x
4x - 12 = -2 => x = 2.5

$again, S_2O_3(aq)+2Br(l)+5H_2O(l)--->2SO_4^{2-}(aq) + 4Br^-(aq)+10H^+(aq)$
oxidation number of S in SO4^2- is x
x - 8 = -2 => x = +6

hence, that's why the same reactant, thiosulphate react differently with bromine and iodine.