Question

Potassium dichromate solution is added to an acidified

solution containing a mixture of KI and FeSO4 in drop wise manner,which will oxidize first, predict the reaction spontaneity using the

following standard reduction potentials.

E0(Cr2O72− / H+/ Cr3+)=1.33V

E0 (Fe3+/Fe2+) = +0.77 V

E0(I2/I-)=0.54V​

Answer 1

Potassium dichromate solution will oxidize first.

Given,

Standard reduction potentials:

E₀(Cr₂O₇²⁻ / H⁺/ Cr³⁺)= 1.33V

E₀ (Fe³⁺/Fe²⁺) = +0.77 V

E₀(I²/I⁻)=0.54V​

To find,

Species to oxidize first =?

The reaction spontaneity=?

Solution,

Reduction involves gain of electrons, so the tendency of an electrode to gain electrons is called its reduction potential.

The species having greater reduction potential, has a greater tendency to reduce other species and get oxidized itself, therefore will get oxidized first in a reaction.

According to the given reduction potential:

The species having the greatest reduction potential is

E₀(Cr₂O₇²⁻ / H⁺/ Cr³⁺)= 1.33V

∴ Potassium dichromate solution will oxidize first.

Now,

ΔG=−nFE₀

(Where ΔG is Gibbs free energy change)

ΔG= negative , means the reaction is spontaneous.

ΔG= positive, means the reaction is non- spontaneous.

E₀ = E₀(reduction) + E₀(oxidation)

Hence, Potassium dichromate solution will oxidize first.

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