Given,`{:(E_(Fe^(3+) //Fe)^o + 3e Cr E^o =- 0.036 V),(E_(Fe^(3+) //Fe)^o =- 0.439 V):}`
The value of standard electrode ptoential for the charge,

Options

A. `-0.072 V`
B. `0.385 V`
C. `0.770 V`
D. `-0.270 V`

Answer

C

Explanation

`Fe^(3+) + 3e^(-) rarr Fe, E^(@) = - 0.036 V`
`:. DeltaG_(1)^(@) = -nfE^(@) = -3 xx F(-0.036) = 0.108 xx F`
Also `Fe^(2+) + 2e^(-) rarr Fe, E^(@) = -0.439 V`
`:. DeltaG_(2)^(@) = -2 xx F (-0.439) = 0.878 xx F`
For `Fe_((aq.))^(3+) + e^(-) rarr Fe_((aq.))^(2+)` ltbRrgt `DeltaG^(@) = -1 xx F xx E^(@)`
`:' DeltaG^(@) = DeltaG_(1)^(@) - DeltaG_(2)^(@)`
`:. -F xx E^(@) = 0.108 xx F - 0.878 xx F`
`E^(@) = 0.77 V`