If `E_(Fe^(2+)//Fe)^(@)=-0.440 V` and `E_(Fe^(3+)//Fe^(2+))^(@)=0.770 V`, then `E_(Fe^(3+)//Fe)^(@)` is -

Options

A. `-0.0367V`
B. `-0.33V`
C. `+0.33V`
D. `+0.0367V`

Answer

A

Explanation

`Fe^(+2) +2e^(-) to Fe, triangleG_(1)^(@)=-n_(1) FE_(1)^(@)`
`Fe^(+3)+e^(-) to Fe^(+2), triangleG^(2)^(@)=-n_(2) Fe_(2)^(@)`
`=Fe^(+3)+3e^(-) to Fe, triangleG_(3)^(@)=triangleG_(1)^(@)+triangleG_(2)^(@)`
`-n_(3)FE_(3)^(@)=-n_(1) FE_(1)^(@)-n_(2) FE_(2)^(@)`
`E_(3)^(@)=(n_(1)E_(1)^(@)+n_(2)E_(2)^(@))/(n_(3))=0.0367V`