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PART - 2 CH - 7 Redox Reactions — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistryPART - 2 CH - 7 Redox Reactions2 Marks
Question
What do you meant by Redox titration? Explain.
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Answer

Those titrations in which one substance get oxidised while other get reduced is called redox titration. In these titrations Potassium permanganate,
Potassium dichromate $\left( KMnO _4, K_2 Cr _2 O _7\right)$ etc. are used as oxidizing agents while ferrous sulphate, ferrous ammonium sulphate and oxalic acid etc. are used as reducing agent. The $KMnO _4$ is filled in burette and it work as self indicator. Hence, indicator is not required and at last point pink colour will appear. In other conditions diphenyl amine, N -phenyl anthranilic acid etc. work as indicators.
In titration of $K _2 Cr _2 O _7$, diphenylamine indicator get oxidised and at last point give blue colour. By these titrations we calculate the strenghs of oxidants and reductants.
The titration between $CuSO _4$ (copper sulphateoxidizing agent) and $Na _2 S_2 O _3$ (sodium thiosulphatereducing agent) is a prime example of redox titration. In this titration KI is used due to which the $I ^{-}$obtained get oxidized by $Cu ^{+2}$ ions and gets converted into $I _2$.
$2 Cu ^{2+}( aq )+4 I ^{-}( aq ) \longrightarrow Cu _2 I _2( aq )+ I _2( aq )$
Here the starch indicator is used which gives blue colour with $I _2$. Then $I _2$ reacts with $S _2 O _3{ }^{-2}$ ion and at end point the solution becomes colourless.
$I _2( aq )+2 S_2 O _3{ }^{2-}( aq ) \longrightarrow 2 I ^{-}( aq )+ S _4 O _6{ }^{2-}( aq )$
$I _2$ is insoluble in water. Hence in solution of KI, it remain as solute in form of $KI _3$.
In this titration, iodine has been produced in the reaction instead of being taken directly, hence this type of titration are called iodometric titrations and those titrations in which iodine solution is taken directly and its action is done with sodium thiosulphate, then it is called iodimetric titration.

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