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The formal potential of Fe^(3+)//Fe^(2+)...

The formal potential of `Fe^(3+)//Fe^(2+)` in a sulphuric acid and phosphoric acid mixture `(E^@= + 0.61 V)` is much lower than the standard potential (`E^@` =+0.77 V). This is due to
(i) formation of the species `[FeHPO_4]^+`
(ii) lowering of potential upon complexation
(iii) formation of the species `[FeSO_4]^+`
(iv) high acidity of the medium.

A

(i) and (ii) only

B

(i), (ii) and (iv) only

C

(iii) only

D

all of these.

Text Solution

Verified by Experts

The correct Answer is:
A
In the aqueous solution, if `H_2SO_4` is present then iron will from hydrated iron sulphate rather than forming `[FeSO_4]^+` solution. Moreover, tendency of formation of `FeSO_4` or `Fe_2(SO_4)_3` is even more . Formation of `[FeHPO_4]^+` is reasonably fine. Due to the formation of complex, `[Fe^(3+)]` decreases and accordingly, potential decreases.
`E=E^@-0.0591/n "log"_10 ([Fe^(2+)])/([Fe^(3+)])`
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