Consider the reactions : 2S_(2)O_(3)^(2-)(aq)+l_(2)(s)toS_(4)O_(6)^(2-)(aq)+2l^(-)(aq) S_(2)O_(3)^(2-)(aq)+2Br_(2)(l)+5H_(2)O(l)to2SO_(4)^(2-)(aq)+4Br^(-)(aq)+10H^(+)(aq) Why does the same reductant, thiosulphate react differently with iodine and bromine?

Consider the reactions : 2S_(2)O_(3)^(2-)(aq)+l_(2)(s)toS_(4)O_(6)^(2

1.	Consider the reactions : 2S_(2)O_(3)^(2-)(aq)+l_(2)(s)toS_(4)O_(6)^(2-)(aq)+2l^(-)(aq) S_(2)O_(3)^(2-)(aq)+2Br_(2)(l)+5H_(2)O(l)to2SO_(4)^(2-)(aq)+4Br^(-)(aq)+10H^(+)(aq) Why does the same reductant, thiosulphate react differently with iodine and bromine?
Answer» Solution :The oxidation numbers of S in the INVOLVED species are as follows: `S_(2)O_(3)^(2-):+2,S_(4)O_(6)^(2-):+2.5,SO_(4)^(2-):+6` Bromine is a stronger oxidising agent than `l_(2)`. Therefore, it oxidises `S_(2)O_(3)^(2-)` (O.N. of S=+2) to `SO_(4)^(2-)` (O.N. of S=+6) in which is in a higher oxidation state. `l_(2)` being a weaker oxidising agent is able to oxidise `S_(2)O_(3)^(2-)` to `S_(4)O_(6)^(2-)` (O.N. of S = 2.5) in which S is in a lower oxidation state. This is why `S_(2)O_(3)^(2-)` REACTS differently with bromine and IODINE.