ElectrochemistryEasy
Question
Given : EoFe3+/Fe = - 0.036 V, EoFe2+/Fe = - 0.439V. The value of standard electrode potential for the change, Fe3+(aq) + e- → Fe2+ (aq) will be :
Options
A.-0.072 V
B.0.385 V
C.0.770 V
D.-0.270
Solution
∵ Fe3+ + 3e- → Fe ; Eo = - 0.036V
∴ ᐃGo1 = - nFEo = -3F(-0.036) = + 0.108 F
Also Fe2+ + 2e- → Fe; Eo = - 0.439 V
∴ ᐃGo2 = - nFEo
= -2 F( - 0.439)
= 0.878 F
To find Eo for Fe3+aq + e- → Fe2+(aq)
ᐃGo = - nFEo
∵ Go = Go1 - Go2
∴ Go = 0.108F - 0.878F
∴ -FEo = + 0.108F - 0.878F
∴ Eo = 0.878 - 0.108
= 0.77v
∴ ᐃGo1 = - nFEo = -3F(-0.036) = + 0.108 F
Also Fe2+ + 2e- → Fe; Eo = - 0.439 V
∴ ᐃGo2 = - nFEo
= -2 F( - 0.439)
= 0.878 F
To find Eo for Fe3+aq + e- → Fe2+(aq)
ᐃGo = - nFEo
∵ Go = Go1 - Go2
∴ Go = 0.108F - 0.878F
∴ -FEo = + 0.108F - 0.878F
∴ Eo = 0.878 - 0.108
= 0.77v
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