Why Fe(III) can be estimated in acidic medium by dicromet not by permanganet? — please give answer basis on value of reduction potential
The ability of a substance to undergo reduction or oxidation reactions can be determined by its reduction potential, also known as standard electrode potential. The reduction potential measures the tendency of a substance to gain or lose electrons in a redox reaction. The more positive the reduction potential, the greater the tendency to undergo reduction.
In the case of Fe(III), it can be estimated in an acidic medium using a dichromate (Cr2O72-) solution because the reduction potential of dichromate (Cr2O72-/Cr3+) is higher than that of permanganate (MnO4-/Mn2+). The reduction potential of dichromate is +1.33 V, while the reduction potential of permanganate is +1.51 V.
When Fe(III) is present in an acidic medium, it can react with dichromate ions as follows:
6Fe3+ + 14H+ + Cr2O72- → 6Fe2+ + 2Cr3+ + 7H2O
This reaction results in the reduction of Fe(III) to Fe(II) and the oxidation of dichromate to chromium (Cr3+). By titrating the Fe(III) solution with a dichromate solution, the amount of Fe(III) can be determined based on the stoichiometry of the reaction.
On the other hand, permanganate cannot be used to estimate Fe(III) in an acidic medium because its reduction potential is higher than that of Fe(III). If permanganate were used, it would preferentially oxidize Fe(II) to Fe(III) rather than being reduced itself. The reduction potential of permanganate is higher (+1.51 V) compared to that of Fe(III) (+0.77 V).
Therefore, based on the difference in reduction potentials, dichromate can be used to estimate Fe(III) in an acidic medium, while permanganate cannot.