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NCERT Class XI Chemistry Redox Reactions Solutions

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Question : 14
Total: 30
Consider the reactions :
2S2O32–(aq)+I2(s) → S4O62–(aq)+2I(aq)–
S2O32–(aq)+2Br2(l)+5H2O(l) → 2SO42–(aq)+4Br(aq)–+10H(aq)+
Why does the same reductant, thiosulphate react differently with iodine and bromine?
Solution:  
The average O.N. of S in S2O32− is +2 while in S4O62− it is +2.5. The O.N. of S in SO42− is +6. Since Br2 is a stronger oxidising agent, it oxidises S of S2O32− to a higher oxidation state of +6 and hence forms SO42− ion. I2, however, being a weaker oxidising agent oxidises S of S2O32− ion to a lower oxidation state of + 2.5 in S4O62− ion.
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