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Home » Consider the reactions : Why does the same reductant, thiosulphate react differently with iodine and bromine?
Consider the reactions : 2 S_{2} O_{3(a q)}^{2-}+I_{2(s)} \rightarrow S_{4} O_{6(a q)}^{2-}+2 I_{(a q)}^{-} S_{2} O_{3(a q)}^{2-}+2 B r_{2(l)}+5 \mathrm{H}_{2} \mathrm{O}_{(l)} \rightarrow 2 S O_{4(a q)}^{2-}+4 B r_{(a q)}^{-}+10 H_{(a q)}^{+} Why does the same reductant, thiosulphate react differently with iodine and bromine?
CBSE | Chemistry | Class 11 | Exercise 1 | NCERT | Redox Reactions
Consider the reactions : 2 S_{2} O_{3(a q)}^{2-}+I_{2(s)} \rightarrow S_{4} O_{6(a q)}^{2-}+2 I_{(a q)}^{-} S_{2} O_{3(a q)}^{2-}+2 B r_{2(l)}+5 \mathrm{H}_{2} \mathrm{O}_{(l)} \rightarrow 2 S O_{4(a q)}^{2-}+4 B r_{(a q)}^{-}+10 H_{(a q)}^{+} Why does the same reductant, thiosulphate react differently with iodine and bromine?

Solution:

The normal oxidation no. of \mathrm{S} in \mathrm{S}_{2} \mathrm{O}_{3}^{2-} is +2.

The normal oxidation no. of \mathrm{S} in S_{4} \mathrm{O}_{6}^{2-} is +2.5.

The oxidation no. of \mathrm{S} in \mathrm{S}_{2} \mathrm{O}_{3}^{2-} is +2.

The oxidation no. of \mathrm{S} in S O_{4}^{2-} is +6.

As B r_{2} is a more grounded oxidizing specialist than I_{2}, it oxidizes \mathrm{S} of \mathrm{S}_{2} \mathrm{O}_{3}^{2-} to a higher oxidation no. of +6 in S O_{4}^{2-}

As I_{2} is a more vulnerable oxidizing specialist so it oxidizes \mathrm{S} of \mathrm{S}_{2} \mathrm{O}_{3}^{2-} particle to a lower oxidation no. that is 2.5 \mathrm{in} S_{4} O_{6}^{2-} particles.

Hence, thiosulphate respond distinctively with I_{2} and B r_{2}.

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