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Redox Reactions

Question
CBSEENCH11006728
Wired Faculty App

Consider the reaction:



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

Solution
The first reaction is,bold space bold space bold 2 bold S subscript bold 2 bold O subscript bold 3 superscript bold 2 bold minus end superscript bold left parenthesis bold aq bold right parenthesis bold space bold plus bold I subscript bold 2 bold left parenthesis bold s bold right parenthesis bold rightwards arrow bold S subscript bold 4 bold O subscript bold 6 superscript bold 2 bold minus end superscript bold left parenthesis bold aq bold right parenthesis bold space bold plus bold 2 bold I to the power of bold minus bold left parenthesis bold aq bold right parenthesis bold average bold space bold Oxidation bold space bold number bold space bold in bold space bold S subscript bold 2 bold O subscript bold 3 superscript bold 2 bold minus end superscript bold space bold is bold space bold plus bold 2 bold average bold space bold Oxidation bold space bold number bold space bold in bold space bold S subscript bold 4 bold O subscript bold 6 superscript bold 2 bold minus end superscript bold space bold is bold space bold 2 bold. bold 5
I2 being a weaker oxidant oxidises S of space space straight S subscript 2 straight O subscript 3 superscript 2 minus end superscript an ion to a lower oxidation state of 2.5 in space space space straight S subscript 2 straight O subscript 6 superscript 2 minus end superscript ion.
The second reaction is,
bold space bold space bold S subscript bold 2 bold O subscript bold 3 superscript bold 2 bold minus end superscript bold left parenthesis bold aq bold right parenthesis bold space bold plus bold 2 bold Br subscript bold 2 bold left parenthesis bold l bold right parenthesis bold space bold plus bold 5 bold H subscript bold 2 bold O bold left parenthesis bold l bold right parenthesis bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold space bold rightwards arrow bold 2 bold SO subscript bold 4 superscript bold 2 bold minus end superscript bold left parenthesis bold aq bold right parenthesis bold space bold plus bold 4 bold Br to the power of bold minus bold left parenthesis bold aq bold right parenthesis bold plus bold 10 bold H to the power of bold plus bold left parenthesis bold aq bold right parenthesis

Oxidation number of S in SO42-=+6

Since Br2 is a stronger oxidant than I2, it oxidises S of S2O32- to a higher oxidation state of +6 and hence forms SO42- ions. As a result, thiosulphate ions behave differently with I2 and Br2.

Some More Questions From Redox Reactions Chapter

What are direct redox reactions? Give one example.

What are indirect redox reactions?

Write formulas for the following compounds:
(a) Mercury (II) chloride
(b) Nickel (II) sulphate
(c) Tin (IV) oxide
(d) Thallium (I) sulphate
(e) Iron (III) sulphate
(f) Chromium (III) oxide

What are electrolytes?

What are cations and anions?

What is electrolysis?

Mention two uses of electrolysis.

Define oxidation number of an element.

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